What are Probiotics?

Probiotics are supplements or foods that contain live microorganisms (in most cases, bacteria but also include yeasts) that are similar to beneficial microorganisms found in the human gut and may be beneficial to health ¹. The International Scientific Association for Probiotics and Prebiotics defines “probiotics” as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host” ². In addition, products containing dead microorganisms and those made by microorganisms (such as proteins, polysaccharides, nucleotides, and peptides) are, by definition, not probiotics. Most probiotics in use today are derived either from fermented foods or from the microbes colonizing a healthy human. The human gastrointestinal tract is colonized by many microorganisms, including bacteria, archaea, viruses, fungi, and protozoa. The activity and composition of these microorganisms (collectively known as the gut microbiota, microbiome or intestinal microflora) can affect human health and disease. Priobiotics are thought to alter the microflora of the host and the live microorganisms are believed to provide health benefits when consumed ³. Products sold as probiotics include foods (such as yogurt), dietary supplements, and products that aren’t used orally, such as such as suppositories and skin creams. Although people often think of them as harmful “germs,” many microorganisms help your bodies to function properly. For example, normal intestinal bacteria digest food, destroy disease-causing microorganisms and produce vitamins. Large numbers of microorganisms live on and in our bodies. In fact, microorganisms in the human body outnumber human cells by 100 to 1. Many of the microorganisms in probiotic products are the same as or similar to the ones in your bodies ⁴. Although a great deal of research has been done on probiotics, much remains to be learned, because not all foods and dietary supplements labeled as “probiotics” on the market have proven health benefits ⁵.

Probiotics should not be confused with prebiotics. The term “prebiotics” refers to nondigestible carbohydrates that act as food for probiotics. Prebiotics are typically complex carbohydrates such as inulin and other fructo-oligosaccharides that microorganisms in the gastrointestinal tract use as metabolic fuel ⁶. Commonly known prebiotics are: oligofructose, inulin, galacto-oligosaccharides, lactulose and breast milk oligosaccharides. Lactulose is a synthetic disaccharide used as a drug for the treatment of constipation and hepatic encephalopathy. The prebiotic oligofructose is found naturally in many foods, such as wheat, onions, bananas, honey, garlic, and leeks. Oligofructose can also be isolated from chicory root or synthesized enzymatically from sucrose. Fermentation of oligofructose in the colon results in a large number of physiologic effects, including ⁷:

• Increasing the numbers of bifidobacteria in the colon
• Increasing calcium absorption
• Increasing fecal weight
• Shortening gastrointestinal transit time
• Possibly lowering blood lipid levels

The increase in colonic bifidobacteria has been assumed to benefit human health by producing compounds to inhibit potential pathogens, by reducing blood ammonia levels, and by producing vitamins and digestive enzymes ⁷.

The term “synbiotics” refers to products that combine both prebiotic sugars and probiotic organisms. Fermented dairy products, such as yogurt and kefir, are considered synbiotic because they contain live bacteria and the fuel they need to thrive. Probiotics are found in foods such as yogurt, while prebiotics are found in whole grains, bananas, onions, garlic, honey and artichokes. In addition, probiotics and prebiotics are added to some foods and available as dietary supplements. Probiotics in dietary supplements are measured in colony forming units (CFU), which indicate the number of viable cells. Amounts may be written on product labels as, for example, 1 x 10⁹ for 1 billion CFU or 1 x 10¹⁰ for 10 billion CFU. Many probiotic supplements contain 1 to 10 billion CFU per dose, but some products contain up to 50 billion CFU or more. However, higher CFU counts do not necessarily improve the product’s health effects.

The term probiotic —meaning “for life”— is currently used to name ingested live microorganisms associated with benefits for humans and animals. The term came into more common use after 1980. The introduction of the concept is generally attributed to Elie Metchnikoff (a Russian scientist, Nobel laureate, and professor at the Pasteur Institute in Paris), who postulated that yogurt-consuming Bulgarian peasants lived longer lives because of this custom ¹. He suggested in 1907 that “the dependence of the intestinal microbes on the food makes it possible to adopt measures to modify the flora in our bodies and to replace the harmful microbes by useful microbes”. Data from the 2012 National Health Interview Survey show that about four million U.S. adults had used probiotics or prebiotics in the past 30 days. Other than vitamins and minerals, probiotics or prebiotics were the third most commonly used dietary supplement. Their use quadrupled between 2007 and 2012. The survey also showed that 300,000 children ages 4 to 17 had used probiotics or prebiotics in the prior 30 days ⁴.

Although there are numerous claimed benefits of using commercial probiotics, such as reduction of gastrointestinal discomfort or strengthening of the immune system, such claims are not backed by scientific evidence. And it is important to be aware that the U.S. Food and Drug Administration (FDA) has not approved any health claims for probiotics.

Although more research is needed, there’s encouraging evidence that probiotics may help:

• Treat diarrhea, especially following treatment with certain antibiotics (e.g., prevention of antibiotic-associated diarrhea including diarrhea caused by Clostridium difficile)
• Prevent and treat vaginal yeast infections and urinary tract infections
• Treat irritable bowel syndrome
• Treat inflammatory bowel disease
• Speed treatment of certain intestinal infections
• Prevent or reduce the severity of common colds and flu
• Allergic disorders such as atopic dermatitis (eczema) and allergic rhinitis (hay fever)
• Tooth decay, periodontal disease, and other oral health problems
• Colic in infants
• Liver disease
• Prevention of necrotizing enterocolitis in very low birth weight infants.

A great deal of research has been done on probiotics, but much remains to be learned about whether they’re helpful and safe for various health conditions.

You don’t necessarily need probiotics — a type of “good” bacteria — to be healthy. However, these microorganisms may help with digestion and offer protection from harmful bacteria, just as the existing “good” bacteria in your body already do.

What kinds of microorganisms are in Probiotics?

Probiotics may contain a variety of microorganisms. Probiotics are identified by their specific strain, which includes the genus, the species, the subspecies (if applicable), and an alphanumeric strain designation ⁸. The seven core genera of microbial organisms most often used in probiotic products are Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus. Table 1 shows examples of the nomenclature used for several commercial strains of probiotic organisms.

The most common are bacteria that belong to groups called Lactobacillus and Bifidobacterium. Each of these two broad groups includes many types of bacteria. Other bacteria may also be used as probiotics, and so may yeasts such as Saccharomyces boulardii ⁴.

Table 1. Nomenclature for sample commercial strains of probiotics

Genus	Species	Subspecies	Strain Designation	Strain Nickname
Lactobacillus	rhamnosus	none	GG	LGG
Bifidobacterium	animalis	lactis	DN-173 010	Bifidus regularis
Bifidobacterium	longum	longum	35624	Bifantis

[Source ⁸ ]

Sources of Probiotics

Food sources of probiotics

Fermented foods are made through the growth and metabolic activity of a variety of live microbial cultures. Many of these foods are rich sources of live and potentially beneficial microbes. Some fermented foods, such as sourdough bread and most commercial pickles, are processed after they are fermented and do not contain live cultures in the form in which they are consumed. Many commercial yogurts, another type of fermented food, contain probiotic microorganisms, such as Lactobacillus bulgaricus and Streptococcus thermophilus.

The live microorganisms used to make many fermented foods, including yogurt, typically survive well in the product throughout its shelf life. However, they usually do not survive transit through the stomach and might not resist degradation in the small intestine by hydrolytic enzymes and bile salts and, therefore, might not reach the distal gut ⁹. However, legitimate probiotic strains contained in yogurt or other foods do survive intestinal transit.

Fermented foods that contain live cultures but do not typically contain proven probiotic microorganisms include many cheeses, kimchi (a Korean fermented cabbage dish), kombucha (a fermented tea), sauerkraut (fermented cabbage), miso (a fermented soybean-based paste), pickles, and raw unfiltered apple cider vinegar made from fermented apple sugars ⁹.

Certain unfermented foods, such as milks, juices, smoothies, cereals, nutrition bars, and infant and toddler formulas, have added microorganisms. Whether these foods are truly probiotics depends on the microorganism levels they contain when they are eaten, whether they survive intestinal transit, and whether their specific species and strains have health effects.

Dietary supplements

Probiotics are also available as dietary supplements (in capsules, powders, liquids, and other forms) containing a wide variety of strains and doses. These products often contain mixed cultures of live microorganisms rather than single strains. The effects of many commercial products containing “probiotics” have not been examined in research studies, and it is difficult for people not familiar with probiotic research to determine which products are backed by evidence. However, some organizations have systematically reviewed the available evidence and developed recommendations on specific probiotics—including appropriate product, dose, and formulation—to use for preventing or treating various health conditions ¹⁰.

Probiotics in dietary supplements are measured in colony forming units (CFU), which indicate the number of viable cells. Amounts may be written on product labels as, for example, 1 x 10⁹ for 1 billion CFU or 1 x 10¹⁰ for 10 billion CFU. Many probiotic supplements contain 1 to 10 billion CFU per dose, but some products contain up to 50 billion CFU or more. However, higher CFU counts do not necessarily improve the product’s health effects.

Current labeling regulations only require manufacturers to list the total weight of the microorganisms on probiotic products’ Supplement Facts labels; this cellular mass can consist of both live and dead microorganisms and, therefore, has no relationship with the number of viable microorganisms in the product ¹¹. Manufacturers may now voluntarily list the CFUs in a product in addition to total microorganism weight on the Supplement Facts label. Because probiotics must be consumed alive to have health benefits and they can die during their shelf life, users should look for products labeled with the number of CFU at the end of the product’s shelf life, not at the time of manufacture.

Usefulness of probiotics

Expert bodies of health professionals make no recommendations for or against probiotic use by healthy people. For people with various health conditions, however, published studies and reviews provide some guidance (as described below) on probiotic species, strains, and doses that might alleviate their symptoms.

The World Gastroenterology Organisation  ⁸ notes that the optimal dose of probiotics depends on the strain and product. The World Gastroenterology Organisation therefore recommends that clinicians who advise their patients to use probiotics specify the probiotic strains, doses, and duration of use that studies in humans have shown to be beneficial ⁸. The World Gastroenterology Organisation guidelines include a summary of evidence on specific probiotic strains used in studies for specific gastrointestinal endpoints ⁸. Finally, the World Gastroenterology Organisation recommends that probiotic supplement users check the labels of probiotic supplements for recommended storage conditions; for example, some require refrigeration, whereas others can be stored at room temperature.

The International Scientific Association for Probiotics and Prebiotics advises manufacturers to list the total number of colony forming units (CFUs)—ideally for each strain—on the “expiration” or “use by” date on the product label ¹². The association also suggests that consumers of these supplements avoid products that list the number of CFUs “at time of manufacture” because this information does not account for declines in CFUs over a product’s lifespan.

Some probiotics may help to prevent diarrhea that’s caused by infections or antibiotics. Probiotics may also help with symptoms of irritable bowel syndrome (IBS). However, benefits have not been conclusively demonstrated, and not all probiotics have the same effects. In other word, research findings for one probiotic strain cannot be extrapolated to others ¹³.

Decades of study on specific probiotic strains have revealed particular health benefits – however, remember that not all these benefits will be delivered by any one product ¹⁴:

• Helping reduce the incidence and duration of antibiotic-associated diarrhea
• Helping manage digestive discomfort (including in irritable bowel syndrome)
• Helping reduce colic symptoms in breastfed babies and occurrence of atopic issues such as eczema in infants
• Helping reduce necrotizing enterocolitis in preterm infants
• Helping reduce symptoms of lactose maldigestion
• Treating acute pediatric infectious diarrhea
• Decreasing the risk or duration of upper respiratory tract infections (such as the common cold) or gut infections
• An increasing number of studies also support probiotic health benefits beyond the digestive tract: for oral care in children and for liver health, bacterial vaginosis, urinary tract infections, and other indications in adults.

The human gastrointestinal tract is colonized by many microorganisms, including bacteria, archaea, viruses, fungi, and protozoa. The activity and composition of these microorganisms (collectively known as the gut microbiota, microbiome, or intestinal microflora) can affect human health and disease.

Probiotics exert their effects usually in the gastrointestinal tract, where they may influence the intestinal microbiota. Probiotics can transiently colonize the human gut mucosa in highly individualized patterns, depending on the baseline microbiota, probiotic strain, and gastrointestinal tract region ¹⁵.

Probiotics also exert health effects by nonspecific, species-specific, and strain-specific mechanisms ². The nonspecific mechanisms vary widely among strains, species, or even genera of commonly used probiotic supplements. These mechanisms include inhibition of the growth of pathogenic microorganisms in the gastrointestinal tract (by fostering colonization resistance, improving intestinal transit, or helping normalize a perturbed microbiota), production of bioactive metabolites (e.g., short-chain fatty acids), and reduction of luminal pH in the colon. Species-specific mechanisms can include vitamin synthesis, gut barrier reinforcement, bile salt metabolism, enzymatic activity, and toxin neutralization. Strain-specific mechanisms, which are rare and are used by only a few strains of a given species, include cytokine production, immunomodulation, and effects on the endocrine and nervous systems. Through all of these mechanisms, probiotics might have wide-ranging impacts on human health and disease.

Because effects of probiotics can be specific to certain probiotic species and strains, recommendations for their use in the clinic or in research studies need to be species and strain specific ⁸. Furthermore, pooling data from studies of different types of probiotics can result in misleading conclusions about their efficacy and safety.

Safety of probiotics

Many probiotic strains derive from species with a long history of safe use in foods or from microorganisms that colonize healthy gastrointestinal tracts. In healthy people, probiotics usually have only minor side effects, if any. However, in people with underlying health problems (for example, weakened immune systems), serious complications such as infections have occasionally been reported. Most probiotics in use today are derived either from fermented foods or from the microbes colonizing a healthy human ⁸. On the basis of the prevalence of Lactobacillus species (acidophilus, casei, fermentum, gasseri, johnsonii, paracasei, plantarum, rhamnosus, and salivarius) in fermented food, as normal colonizers of the human body and the low level of infection attributed to them, their pathogenic potential is deemed to be quite low by experts in the field ⁸. Bifidobacterium species (adolescentis, animalis, bifidum, breve, and longum) enjoy a similar safety record ⁸. Most products are designed for the generally healthy population, so use in persons with compromised immune function or serious underlying disease is best restricted to the strains and indications with proven efficacy. Testing or use of newly isolated probiotics in other disease indications is only acceptable after approval by an independent ethics committee. Traditional lactic acid bacteria, long associated with food fermentation, are generally considered safe for oral consumption as part of foods and supplements for the generally healthy population and at levels traditionally used ⁸.

Given the large quantities of probiotics consumed around the world, the numbers of opportunistic infections that result from currently marketed probiotics are negligible. For example, probiotics have been administered to thousands of newborn infants, including some who were premature, without a single case of sepsis ¹⁶. However, some clinical trials of probiotics are not designed to adequately address questions about safety, leaving gaps in available safety evidence ¹⁷, ¹⁸.

Side effects of probiotics are usually minor and consist of self-limited gastrointestinal symptoms, such as gas. In a few cases, mainly involving individuals who were severely ill or immunocompromised, the use of probiotics has been linked to bacteremia, fungemia (fungi in the blood), or infections that result in severe illness ¹⁹, ²⁰. However, some case reports did not confirm that the specific strain of probiotics used was the cause of the infection. In other cases, the probiotic strain used was confirmed to be the opportunistic pathogen. Because species used as probiotics can be normal residents of a patient’s microbiota, such confirmation is important.

At least 60 reports have been published since 1966 of fungemia associated with the use of probiotics containing the yeast Saccharomyces cervisiae. In many of these cases, the patients were in an intensive care unit (ICU), were receiving enteral or parenteral nutrition, had a central venous catheter, or had received broad-spectrum antimicrobial treatment ²¹. When Lactobacillus rhamnosus GG was introduced into dairy products in Finland in 1990, monitoring of this country’s population through 2000 revealed no increase in rates of bacteremia (bacteria in the blood) caused by Lactobacillus species ²². However, an analysis of 22,174 ICU patients in a Boston hospital found that those who received Lactobacillus rhamnosus GG (typically through a feeding tube) had a markedly higher risk of developing Lactobacillus bacteremia compared to patients who did not receive the probiotic ²³. Of the 522 patients receiving Lactobacillus rhamnosus GG, a genome-level analysis identified six cases where the ingested Lactobacillus rhamnosus GG was found in the blood, compared to only two cases among the 21,652 patients who did not receive the Lactobacillus rhamnosus GG.

For individuals with compromised immune function or other serious underlying diseases, the World Gastroenterology Organisation advises restricting probiotic use to the strains and indications that have proven efficacy ⁸.

Government regulation of probiotics in the United States is complex. Depending on a probiotic product’s intended use, the FDA might regulate it as a dietary supplement, a food ingredient, or a drug. If a probiotic is intended for use as a dietary supplement, it is placed under the umbrella of “foods,” and as such is regulated by FDA’s Center for Food Safety and Applied Nutrition ²⁴.

Many probiotics are sold as dietary supplements, which do not require FDA approval before they are marketed ²⁵. Dietary supplement labels may make claims about how the product affects the structure or function of the body without FDA approval, but they cannot make health claims (claims that the product reduces the risk of a disease) without the FDA’s consent.

If a probiotic is marketed as a drug for specific treatment of a disease or disorder in the future, it will be required to meet more stringent requirements. It must be proven safe and effective for its intended use through clinical trials and be approved by the FDA before it can be sold.

What Do Probiotics Do?

Probiotics may have a variety of effects in the body, and different probiotics may act in different ways. Current insights into the clinical applications for various probiotics or prebiotics ingastroenterology are summarized below.

Probiotics might:

• Help to maintain a desirable community of microorganisms
• Stabilize the digestive tract’s barriers against undesirable microorganisms or produce substances that inhibit their growth
• Help the community of microorganisms in the digestive tract return to normal after being disturbed (for example, by an antibiotic or a disease)
• Outcompete undesirable microorganisms
• Stimulate the immune response.

Under normal or “balanced” conditions, friendly bacteria in the gut outnumber the unfriendly ones. Probiotics can act as gut-beneficial bacteria that create a physical barrier against unfriendly bacteria ²⁶.

Probiotics can also help offset the bacterial imbalance caused by taking antibiotics. Antibiotics kill good bacteria along with the harmful ones, often leading to gas, cramping or diarrhea.

Probiotics may help breakdown protein and fat in the digestive tract — a valuable benefit to help infants, toddlers or patients who need to build strength throughout and after an illness.

Benefits of Probiotics

The potential health benefits of probiotics are the focus of a great deal of scientific research.

Probiotics may help with weight loss

The gut microbiota play an important role in nutrient and energy extraction from food. Research in mice suggests that the gut microbiota affect not only use of energy from the diet, but also energy expenditure and storage within the host ²⁷. Whether these effects translate to humans is unknown.

Results of clinical trials that assessed the impact of probiotics on obesity-related endpoints have been inconsistent. One 12-week clinical trial, for example, randomized 210 healthy adults aged 35 to 60 years who had large amounts of visceral fat to consume 200 g/day fermented milk containing 10⁷, 10⁶, or 0 (control) CFU of Lactobacillus gasseri SBT2055 (LG2055) per gram of milk ²⁸. Participants who received 10⁷ or 10⁶ CFU/g milk of Lactobacillus gasseri experienced significant reductions in visceral fat area (mean reductions of 8.5% and 8.2%, respectively), body mass index (BMI), waist and hip circumference, and body fat mass compared with the control group. In another randomized clinical trial, daily supplementation with 3.24 x 10⁸ CFU Lactobacillus rhamnosus CGMCC1.3724 for 24 weeks combined with an energy-restricted diet for the first 12 weeks (500 kcal/day less than estimated calorie needs) did not significantly affect weight loss compared with placebo in 125 obese adults aged 18 to 55 years ²⁹. However, the Lactobacillus supplementation did significantly reduce body weight after 12 weeks (loss of 1.8 kg) and 24 weeks (loss of 2.6 kg) compared with placebo in the 77 female participants.

A 2017 systematic review of 14 clinical trials, including the two described above, in 1,067 overweight or obese individuals showed that probiotics (mostly Lactobacillus administered at various doses for 3 weeks to 6 months) significantly decreased body weight and/or body fat in nine trials, had no effect in three trials, and increased body weight in two trials ³⁰. Another recent systematic review and meta-analysis of 15 randomized controlled trials in 957 overweight or obese individuals found that supplementation with various doses and strains of probiotics for 3 to 12 weeks resulted in larger reductions in body weight (by 0.6 kg), body mass index (by 0.27 kg/m2), and fat percentage (by 0.6%) than placebo ³¹. However, these effects were small and of questionable clinical significance.

In contrast, the most recent systematic review and meta-analysis, which included 19 randomized trials in 1,412 participants, found that supplementation with probiotics or synbiotics reduced waist circumference slightly (by 0.82 cm) but had no effect on body weight or body mass index, although the quality of evidence was low to moderate ³². The findings from another meta-analysis of 14 trials in 881 adults, 5 trials in 726 children, and 12 trials in 1,154 infants suggested that probiotics promote loss of a mean of 0.54 kg in adults, gain of a mean of 0.20 kg in children, and no significant weight loss or gain in infants ³³.

In a double-blind, placebo-controlled, randomized trial ³⁴ involving 125 obese men and women who took either a probiotic supplement, containing a strain of Lactobacillus rhamnosus, or a placebo without probiotic bacteria during a 12-week weight-loss program and a 12-week weight-maintenance period. Each subject consumed two capsules per d of either a placebo or a Lactobacillus rhamnosus formulation (1·6 × 108 colony-forming units of Lactobacillus rhamnosus/capsule with oligofructose and inulin). Each group was submitted to moderate energy restriction for the first 12 weeks followed by 12 weeks of weight maintenance. Body weight and composition were measured at baseline, at week 12 and at week 24.After the first 12 weeks, women taking the supplement had lost an average of 10 pounds, while those on placebo shed 6 pounds. During the weight-maintenance period, the female probiotic users dropped 2 more pounds on average, while the weight of placebo takers reached a plateau. Men did not seem to benefit from the probiotic ³⁴. The mean weight loss was not significantly different between the Lactobacillus rhamnosus and placebo groups when all the subjects were considered. However, a significant treatment × sex interaction was observed. The mean weight loss in women in the Lactobacillus rhamnosus group was significantly higher than that in women in the placebo group after the first 12 weeks, whereas it was similar in men in the two groups. Women in the Lactobacillus rhamnosus group continued to lose body weight and fat mass during the weight-maintenance period, whereas opposite changes were observed in the placebo group. Changes in body weight and fat mass during the weight-maintenance period were similar in men in both the groups.

After the 12-week maintenance period, the weight of the women in the placebo group had remained stable but the probiotic group had continued to lose weight, for a total of 5.2 kg per person. In short, women consuming probiotics lost twice as much weight over the 24-week period of the study. Researchers also noted a drop in the appetite-regulating hormone leptin in this group, as well as a lower overall concentration of the intestinal bacteria related to obesity.

According to Prof. Angelo Tremblay, the head researcher, probiotics may act by altering the permeability of the intestinal wall. By keeping certain proinflammatory molecules from entering the bloodstream, they might help preventing the chain reaction that leads to glucose intolerance, type 2 diabetes, and obesity.

This study focused on only one strain of Lactobacillus rhamnosus, but Professor Tremblay believes that other probiotics found in dairy products could have a similar effect. He stresses, however, that the benefits of these bacteria are more likely to be observed in a favorable nutritional context that promotes low fat and adequate fiber intake.

Taken together, these results indicate that the effects of probiotics on body weight and obesity might depend on several factors, including the probiotic strain, dose, and duration, as well as certain characteristics of the user, including age, sex, and baseline body weight. Additional research is needed to understand the potential effects of probiotics on body fat, body weight, and obesity in humans.

Probiotics may reduce the risk of developing atopic dermatitis

Atopic dermatitis, the most common form of eczema, is also one of the most common chronic inflammatory skin disorders, affecting approximately 15% to 20% of children and 1% to 3% of adults worldwide ³⁵.

Numerous probiotic studies have evaluated the effects of various species and strains of bacteria on the prevention of atopic dermatitis and several meta-analyses (statistical analyses that combine the results of multiple scientific studies) have synthesized the findings of these studies. These studies and meta-analyses show that exposure to probiotics during pregnancy and in early infancy might reduce the risk of developing atopic dermatitis in children. For example, a 2018 meta-analysis included 27 randomized controlled trials (randomized controlled trials) and one controlled cohort study in a total of 6,907 infants and children exposed to probiotics in utero for 2 weeks to 7 months (via maternal oral supplementation) and/or by oral administration to the infants after birth for 2 to 13 months ³⁶. Between ages 6 months and 9 years, probiotic treatment with single strains or mixtures that included Lactobacillus, Bifidobacterium, and Propionibacterium strains significantly reduced the risk of atopic dermatitis from 34.7% in the control group to 28.5% in the probiotic group.

Subgroup analyses showed that the use of probiotics during both the prenatal and postnatal periods significantly reduced the incidence of dermatitis; however, probiotics taken either prenatally only or postnatally only did not. In addition, the effects of probiotic treatment varied by probiotic strain. For example, supplementation with either Lactobacillus rhamnosus or Lactobacillus paracasei significantly reduced the incidence of atopic dermatitis, whereas supplementation with Lactobacillus reuteri or Lactobacillus acidophilus did not ³⁶.

In contrast, another meta-analysis of 5 randomized clinical trials with a total of 889 participants found that Lactobacillus rhamnosus GG (LGG) supplementation did not reduce the risk of eczema in children up to age 4 years, regardless of the timing of administration (to the mothers during pregnancy and/or during breastfeeding or to the infants directly) ³⁷.

Most published meta-analyses have shown that probiotics slightly reduce atopic dermatitis symptoms in infants and children. For example, a meta-analysis of 13 randomized controlled trials with a total of 1,070 participants aged 18 years or younger found that probiotic treatment for 4 to 8 weeks of those with atopic eczema significantly reduced SCORing Atopic Dermatitis (SCORAD) values, indicating reduced symptom severity ³⁸. Subgroup analyses found probiotics had protective effects in children aged 1 to 18 years (nine trials) but not in infants younger than 1 year (five trials). In addition, treatment with Lactobacillus, Lactobacillus fermentum, or a mixture of probiotic strains, significantly reduced SCORAD values in the children, whereas Lactobacillus rhamnosus GG and Lactobacillus plantarum had no effect ³⁸.

Another meta-analysis included 8 randomized clinical trials with a total of 741 participants from birth to 36 months of age who were treated with Lactobacillus or Bifidobacterium for 4 to 24 weeks ³⁹. The results also suggested that probiotics containing Lactobacillus might reduce atopic dermatitis symptoms in infants and toddlers, but those containing Bifidobacterium did not ³⁹. The treatment significantly improved symptoms in participants with moderate-to-severe forms of the disease but not in those with mild forms. A Cochrane review of 39 randomized controlled trials of single probiotics and probiotic mixtures for the treatment of eczema in 2,599 participants aged 1 to 55 years (most were children) found that probiotic treatment might slightly reduce SCORAD scores ⁴⁰. However, the researchers concluded that the differences were not clinically significant and that the current evidence does not support the use of probiotics for eczema treatment ⁴⁰.

Overall, the available evidence suggests that the use of probiotics might reduce the risk of developing atopic dermatitis and lead to significant reductions in atopic dermatitis SCORAD scores, but these products might provide only limited relief from the condition. Furthermore, the effects of probiotics vary by the strain used, the timing of administration, and the patient’s age, so it is difficult to make recommendations.

Probiotics for treating pediatric acute infectious diarrhea

Acute diarrhea is usually defined as loose or liquid stools and/or an increase in the frequency of bowel movements (typically at least three in 24 hours) ⁴¹. Acute diarrhea can be accompanied by fever or vomiting, and it usually lasts no more than 7 days.

Episodes of acute infectious diarrhea remain a major disease burden throughout the world, especially in developing countries. They are due to infection by many different organisms. Most episodes are self-limiting and usually investigations are not done to identify the infectious agent. The main risk to health is dehydration and management aims to improve and maintain hydration status. However, rehydration fluids do not reduce the stool volume or shorten the episode of diarrhea.

Used alongside rehydration therapy, probiotics appear to be safe and have clear beneficial effects in shortening the duration and reducing stool frequency in acute infectious diarrhea. However, more research is needed to guide the use of particular probiotic regimens in specific patient groups ⁴².

A 2020 Cochrane review of 82 randomized controlled trials in a total of 12,127 participants (11,526 children [age < 18 years] and 412 adults) found that taking single- and multi-strain probiotics does not support the use of probiotics for the treatment of acute infectious diarrhea ⁴³. The 2020 Cochrane review did not detect a difference between taking a probiotic and taking a placebo or no additional treatment in the number of children who had diarrhea longer than 48 hours (two studies in high‐income countries; 1770 children). The 2020 Cochrane review authors are uncertain whether taking probiotics affects the length of time that the symptoms of diarrhea last (six studies; 3058 people) ⁴³. These findings were not affected by age, nutritional and socioeconomic status, region, or rotavirus infection of participants, nor by whether they were taking antibiotic medicines or zinc supplements.

Probiotics probably make little or no difference to the number of people who have diarrhea lasting 48 hours or longer, and the authors are uncertain whether probiotics reduce the duration of diarrhea ⁴³.

Probiotics may not affect how long acute diarrhea lasts. The 2020 Cochrane review authors do not know if probiotics can shorten the time to recovery from diarrhea. We need reliable evidence from further studies to determine whether probiotics help treat acute infectious diarrhea.

The 2020 Cochrane review findings were not affected by age, nutritional and socioeconomic status, region, or rotavirus infection of participants, nor by whether they were taking antibiotic medicines or zinc supplements ⁴³.

Taking probiotics may not have affected:

• how many people had diarrhea longer than 14 days (nine studies; 2928 people); or
• how many people were admitted to hospital with diarrhea (six studies; 2283 people).

It was unclear whether taking probiotics shortened the time spent in hospital compared with taking a placebo or no additional treatment (24 studies; 4056 people). Few studies reported on any unwanted effects of probiotics; no serious unwanted effects were reported among people who took probiotics.

In another review of 11 randomized clinical trials with a total of 2,444 participants showed that Lactobacillus rhamnosus GG is most effective in treating infectious diarrhea at a daily dose of at least 10¹⁰ CFU ⁴⁴. A review of 22 randomized clinical trials with a total of 2,440 participants aged 1 month to 15 years found that Saccharomyces boulardii (most commonly 10⁹ to 10¹⁰ CFU/day for 5–10 days) reduced both duration of diarrhea and stool frequency ⁴⁵. In both of these analyses, Lactobacillus rhamnosus GG and Saccharomyces boulardii reduced the duration of acute infectious diarrhea by approximately 1 day. However, two subsequent clinical trials found that a 5-day course of LGG (1×10¹⁰ CFU twice per day taken alone in one trial and a total of 4×10⁹ CFU twice per day of LGG and L. helveticus R0052 in the other) was no better than placebo at treating or improving the outcomes of acute gastroenteritis in 1,729 infants and small children presenting to pediatric emergency departments ⁴⁶, ⁴⁷.

Based on a requirement of at least two adequate and well-controlled studies, each convincing on its own, to establish an intervention’s effectiveness, the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition identified two probiotic supplements, Lactobacillus rhamnosus GG (typically at ≥10¹⁰ CFU/day for 5–7 days) and Saccharomyces boulardii (typically at 250–750 mg/day [10⁹–10¹⁰ CFU] for 5–7 days), for which evidence supported use as adjuncts to rehydration for managing acute infectious diarrhea in pediatric patients ¹⁰. However, recent studies suggest that probiotics might not be efficacious in developed country emergency departments because most episodes of acute infectious diarrhea are self-limiting and require no treatment other than rehydration therapy ⁴⁶, ⁴⁷. Therefore, the cost-effectiveness of the use of probiotic supplements to manage acute viral diarrhea lacks consensus ¹⁰.

Probiotics for the prevention antibiotic-associated diarrhea

Antibiotic-associated diarrhea occurs when antibiotics disturb the natural balance of “good” and “bad” bacteria in the intestinal tract, causing harmful bacteria to multiply beyond their normal numbers. The symptoms of antibiotic-associated diarrhea include frequent watery bowel movements and crampy abdominal pain. Antibiotics are another common cause of acute-onset diarrhea. Antibiotic treatment often disturbs the intestinal microbiota and, by decreasing microbial diversity, can lead to a loss of microbial metabolism (resulting in osmotic diarrhea due to excessive fluid in the intestine), loss of colonization resistance (resulting in increased numbers of infections by other pathogens), and increased intestinal motility ⁴⁸. Up to 30% of patients who use antibiotics experience antibiotic-associated diarrhea ⁴⁹.

Individuals receiving inpatient care are at significantly greater risk of developing antibiotic-associated diarrhea than individuals receiving outpatient care. Similarly, children younger than 2 years and seniors older than 65 years are at greater risk of developing antibiotic-associated diarrhea than other children and adults. Some antibiotics (e.g., erythromycin and penicillin) are associated with antibiotic-associated diarrhea more often than others ⁴⁹.

Meta-analyses indicate that the use of any of a few species and strains (described below) of probiotics might reduce the risk of antibiotic-associated diarrhea by 51% ⁵⁰. However, the benefits of probiotic use to prevent antibiotic-associated diarrhea depend on the type of antibiotic that caused the antibiotic-associated diarrhea, the strain(s) of probiotic used, the life stage of the user (child, younger adult, or older adult), and whether the user is receiving inpatient or outpatient care. Positive associations between intakes of probiotics and reduced risk of antibiotic-associated diarrhea have been found in children and adults aged 18 to 64 years but not in adults aged 65 years and older ⁵¹.

Both Lactobacillus rhamnosus GG and Saccharomyces boulardii have been shown to reduce the risk of antibiotic-associated diarrhea. In a systematic review and meta-analysis of 12 randomized controlled trials with a total of 1,499 children and adults, treatment with Lactobacillus rhamnosus GG (4 x 10⁸ to 12 x 10¹⁰ CFU) compared with placebo or no additional treatment for 10 days to 3 months reduced the risk of antibiotic-associated diarrhea in patients treated with antibiotics from 22.4% to 12.3% ⁵². However, when the 445 children and 1,052 adults were evaluated separately, the difference was statistically significant in children only. Although the optimal dose of Lactobacillus rhamnosus GG is unclear, 1 to 2 x 10¹⁰ CFU/day reduced antibiotic-associated diarrhea risk in children by 71% ⁵². Taking probiotics within 2 days of the first antibiotic dose is more effective than starting to take them later.

In a systematic review and meta-analysis of 21 randomized controlled trials in a total of 4,780 participants, treatment with Saccharomyces boulardii compared with placebo or no treatment reduced the risk of antibiotic-associated diarrhea in 3,114 adults treated with antibiotics from 17.4% to 8.2% ⁵². In the 1,653 children in this study, Saccharomyces boulardii reduced the risk from 20.9% to 8.8%. Various doses of Saccharomyces boulardii were tested, and no clear dose-dependent effects were observed.

Overall, the available evidence suggests that starting probiotic treatment with Lactobacillus rhamnosus GG or Saccharomyces boulardii within 2 days of the first antibiotic dose helps reduce the risk of antibiotic-associated diarrhea in children and adults aged 18 to 64, but not in elderly adults. There is no evidence to suggest that the benefits are greater when more than one probiotic strain is used.

Probiotics may prevent radiation-induced diarrhea

The gut microbiota may play an important role in radiation-induced diarrhea by reinforcing intestinal barrier function, improving innate immunity and stimulating intestinal repair mechanisms. A 2013 meta-analysis ⁵³ concluded that probiotics may be beneficialin the prevention and possibly in the treatment of radiation-induced diarrhea.

Probiotics may reduce some symptoms of IBS (irritable bowel syndrome)

Irritable bowel syndrome (IBS) is a common functional disorder that affects the large intestine and causes symptoms such as abdominal pain, bloating, cramping, constipation, and diarrhea. With IBS, you have these symptoms without any visible signs of damage or disease in your digestive tract. As many as one in five Americans have symptoms of IBS ⁵⁴. Women are up to two times more likely than men to develop IBS ⁵⁴. People younger than age 50 are more likely to develop IBS than people older than age 50 ⁵⁵. The cause of IBS isn’t well understood growing evidence suggests potential roles for intestinal microbiota in its pathophysiology and symptoms; IBS has also been linked to stress, large meals, certain foods, and alcohol ⁵⁶. IBS is a functional gastrointestinal disorder. Functional gastrointestinal disorders, which doctors now call disorders of gut-brain interactions, are related to problems with how your brain and your gut work together ⁵⁷. These problems can cause your gut to be more sensitive and change how the muscles in your bowel contract. If your gut is more sensitive, you may feel more abdominal pain and bloating. Changes in how the muscles in your bowel contract lead to diarrhea, constipation, or both.

According to this research, proinflammatory bacterial species, including Enterobacteriaceae, are abundant in patients with IBS, who typically also have a corresponding reduction in amounts of Lactobacillus and Bifidobacterium ⁵⁸. Probiotic products commonly contain Lactobacillus and Bifidobacterium and, therefore, have the potential to restore some missing microbial functionality and, consequently, help manage IBS symptoms. Although probiotics are a promising and reasonable treatment option for IBS, the overall quality and quantity of evidence are relatively weak.

Several meta-analyses have assessed the role of probiotics in patients with IBS ⁵⁹, ⁶⁰, ⁶¹, ⁶², ⁶³, ⁶⁴. Most have found that probiotics have a positive, although modest, beneficial effect. For example, a meta-analysis of 23 randomized controlled trials in a total of 2,575 patients found that, overall, probiotics reduced the risk that IBS symptoms would persist or not improve by 21% ⁶⁰. Probiotics are somewhat effective in children and adults with irritable bowel syndrome (IBS) and in children with functional abdominal pain ⁶⁵. A guideline and meta-analysis of 23 trials involving 2,575 children and adults with IBS found that probiotics significantly improved global symptoms, bloating, and flatulence compared with placebo, but the quality of studies was low ⁶⁶. A meta-analysis of 21 randomized controlled trials involving 1,639 adults with IBS found that probiotics significantly improved overall symptom response and quality of life compared with placebo ⁶⁷. A meta-analysis of children with IBS or functional abdominal pain found that probiotics increased the likelihood of treatment success compared with placebo and decreased abdominal pain intensity; however, there was no effect on abdominal pain frequency ⁶⁸.

A 2018 review of 53 studies (5,545 total participants) of probiotics for irritable bowel syndrome (IBS) concluded that probiotics may have beneficial effects on global IBS symptoms and abdominal pain, but it was not possible to draw definite conclusions about their effectiveness or to identify which species, strains, or combinations of probiotics are most likely to be helpful ⁵⁹.

Various species and strains of probiotics had beneficial effects on global IBS symptoms, abdominal pain, bloating, and flatulence scores, but the quality of the studies was low. Some combinations of probiotics were superior to individual strains in this analysis, but no specific combination was superior to another. A second meta-analysis of 15 randomized- controlled trials in a total of 1,793 patients with IBS found that probiotics reduced overall symptoms and abdominal pain more than placebo after 8 to 10 weeks of therapy; in children, these supplements also improved mucosal barrier function ⁶¹.

A more recent systematic review included 35 randomized controlled trials of 16 single-strain and 19 multi-strain products in 3,406 adults with IBS ⁶⁹. Of the studies that found a statistically significant reduction in global symptoms (14 of 29 trials) or a clinically meaningful reduction in abdominal pain (8 of 34 trials), most used multi-strain probiotic products. Furthermore, only trials of multi-strain products found a clinically meaningful improvement in quality of life ⁶², ⁶³.

Whether different strains of probiotic bacteria have beneficial effects on IBS probably depends on the IBS symptom being evaluated ⁷⁰. In a meta-analysis of 10 randomized controlled trials with a total of 877 adults treated with probiotics or placebo for 4 weeks to 6 months, pain scores improved significantly with administration of probiotics containing Bifidobacterium breve, Bifidobacterium longum, or Lactobacillus acidophilus species compared with placebo treatment ⁷¹. In contrast, Streptococcus salivarius ssp. thermophilus, Bifidobacterium animalis, Bifidobacterium infantis, Lactobacillus casei, Lactobacillus plantarum, Lactobacillus bulgaricus, and Saccharomyces boulardii had no significant effect. The abdominal distension scores improved with use of probiotics containing Bifidobacterium breve, Bifidobacterium infantis, Lactobacillus casei, or Lactobacillus plantarum species. Flatulence declined with use of all tested probiotics, but the studies showed no positive effect of probiotics on quality of life.

Overall, the available evidence indicates that probiotics might reduce some symptoms of IBS. However additional high-quality clinical trials are needed to confirm the specific strain, dose, and duration of treatment required as well as the type of IBS (such as with predominant diarrhea or constipation) that can be treated effectively with probiotics.

Patients should consider starting probiotics at the onset of symptoms and continue as needed for persistent symptoms.

Probiotics to prevent Clostridium difficile diarrhea associated with antibiotic use

Antibiotics are among the most prescribed medications worldwide. Antibiotic treatment may disturb the balance of organisms that normally inhabit the gut. This can result in a range of symptoms, most notably, diarrhea. Clostridium difficile is one particularly dangerous organism that may colonize the gut if the normal healthy balance has been disturbed. Clostridium difficile-related disease varies from asymptomatic infection, diarrhea, colitis, and pseudo-membranous colitis to death. The cost of treatment is expensive and the financial burden on the medical system is substantial. The recent increase in incidence and severity of disease caused by hypervirulent strains of C. difficile has prompted some clinicians to prescribe probiotics as drugs in combination with standard antimicrobial drug therapy for these patients.

Based on this systematic review and meta-analysis of 23 randomized controlled trials including 4213 patients, moderate quality evidence suggests that probiotics are both safe and effective for preventing Clostridium difficile-associated diarrhea ⁷². The study results suggested that when probiotics are given with antibiotics they reduce the risk of developing Clostridium difficile-associated diarrhea by 64%. Side effects were assessed in 26 studies (3964 participants) and the results suggest that probiotics decrease the risk of developing side effects. The most common side effects reported in these studies include abdominal cramping, nausea, fever, soft stools, flatulence, and taste disturbance. The short-term use of probiotics appears to be safe and effective when used along with antibiotics in patients who are not immunocompromised or severely debilitated.

A 2016 meta-analysis ⁷³ concluded that probiotics can reduce the risk of developing Clostridium difficile–associated diarrhea in patients receiving antibiotics. However, the authors caution that additional studies are needed in order to determine the best dosage and strain.

Probiotics for persistent diarrhea in children

Persistent diarrhoea is defined as a diarrhoeal episode that starts acutely but then lasts for 14 days or more, and it is an important cause of morbidity and mortality in children under five years old in developing countries throughout the world. The cause of persistent diarrhoea is not completely understood but is likely to be complex; this in turn makes management of the condition difficult. Probiotics are bacteria and yeasts that are similar to the normal bacteria found in a healthy gut. These so called friendly bacteria have been used in several studies to treat acute infectious diarrhoea with encouraging results. This review found four trials involving children with persistent diarrhoea. Two studies with a combined total of 324, showed that probiotics shorten the duration of diarrhoea and reduce the stool frequency on day-5. One study (235 children) suggested that probiotics reduce the hospital stay. Three out of four trials reported that no adverse events occurred. However, this review is limited by few trials with small number of participants, and therefore may not represent a reliable estimate of probiotics’ effect ⁷⁴.

Probiotics for prevention of necrotizing enterocolitis in preterm infants

Necrotizing enterocolitis is a serious disease that affects the bowel of premature infants in the first few weeks of life. Although the cause of necrotizing enterocolitis is not entirely known, milk feeding and bacterial growth play a role. Probiotics (dietary supplements containing potentially beneficial bacteria or yeast) have been used to prevent necrotizing enterocolitis. This Cochrane Review of studies found that the use of probiotics reduces the occurrence of necrotizing enterocolitis and death in premature infants born weighing less than 1500 grams, although not all probiotic preparations tested are effective ⁷⁵. The number needed to treat to prevent one death from all causes by treatment with probiotics is 20. Furthermore, there is insufficient data with regard to the benefits and potential adverse effects of probiotics in the most at risk infants weighing less than 1000 grams at birth.

Probiotics may ease constipation

Researchers at King’s College in London ⁷⁶ scoured the medical literature and found 14 studies that met their criteria for a well-done study. All were clinical trials that randomly assigned people with constipation to take either probiotics or a placebo (or other control treatment).

By pooling the findings of the trials, the researchers found that on average, probiotics slowed “gut transit time” by 12.4 hours, increased the number of weekly bowel movements by 1.3, and helped soften stools, making them easier to pass ⁷⁶. Probiotics that contained Bifidobacterium appeared to be the most effective. Adequately powered randomised clinical trials are required to better determine the species or strains, doses, and duration of use of probiotics that are most efficacious.

Probiotics to prevent Upper Respiratory Tract Infections (for example, the common cold)

With the increasing consumption of probiotics, researchers carried out a review on the effects of probiotics in helping people (without immunodeficiencies) to avoid acute upper respiratory tract infections, for example, the common cold, compared to placebo. Upper respiratory tract infections include the common cold and inflammation of the trachea and larynx, with symptoms including fever, cough, pain and headaches. Most acute upper respiratory tract infections are caused by viral infections and usually resolve after three to seven days. Some probiotics (live micro-organisms) can confer a health benefit to the patient when administered in adequate amounts. Lactic acid bacteria and bifidobacteria are the most common types of probiotics. The quality of the evidence is low or very low mainly due to poorly conducted trials, but study on probiotics vs placebo as treatment for the common cold, probiotics were better than placebo in reducing the number of participants experiencing episodes of acute upper respiratory tract infections by about 47% and the duration of an episode of acute upper respiratory tract infections by about 1.89 days ⁷⁷.

Probiotics potential treatment for Acne and Rosacea

In an article published by the American Academy of Dermatology ⁷⁸. Current treatment includes diet with or without medication ⁷⁹.

Probiotics – ‘good’ bacteria that are usually taken in the form of capsules or drinks – supplement the gut bacteria. They have the potential to change a person’s metabolism and so prevent gestational diabetes mellitus. This review ⁷⁹ was designed to look at whether there is evidence to show if this is true or not. At the moment there is only one randomised controlled study, which involved 256 women. This study does show a lower rate of gestational diabetes mellitus in women who took probiotics from early pregnancy, with the rate of diagnosis of gestational diabetes mellitus being reduced by two-thirds and their babies on average weighed 127 g less at birth. This study did not find differences in the rates of miscarriage, intrauterine or neonatal death or stillbirth. There was no clear evidence of a change in the proportion of women delivered by caesarean section or in the risk of preterm delivery. The study did not report on how much weight the mothers gained during pregnancy or how many babies were large-for-gestational age or that weighed more than 4000 g at birth or on the body composition of the babies. One study is not enough to draw any definite conclusions at the moment. There are other studies underway.

Probiotics may reduce high cholesterol

High levels of cholesterol in the blood (hypercholesterolemia) or cholesterol trapped in arterial walls are a risk factor for cardiovascular disease (CVD). Low-density lipoprotein (LDL also known as “bad” cholesterol) carries cholesterol to tissues and arteries. The higher the LDL level, the greater the risk is for cardiovascular disease. High-density lipoprotein (HDL also known as “good” cholesterol) carries cholesterol from the tissues to the liver and leads to its excretion. A low level of HDL increases a person’s risk of cardiovascular disease.

Researchers have studied the use of probiotics to improve lipid profiles. The mechanisms of their effects on cholesterol concentrations include catabolism of cholesterol by increasing:

• Bile salt hydrolase activity, which increases the need for new bile acids and thus reduces serum cholesterol levels ⁸⁰, ⁸¹;
• Binding of cholesterol in the small intestine, which reduces the amount that the body absorbs;
• Assimilation and incorporation of cholesterol into bacteria ⁸⁰, thus lowering cholesterol levels in blood;
• Production by lactobacilli and bifidobacteria of short-chain fatty acids, which lower hepatic cholesterol synthesis and regulate cholesterol metabolism ⁸².

A meta-analysis of 30 randomized controlled trials with 1,624 participants (mostly adults aged 18 years or older) demonstrated that those treated with probiotics for 3 to 12 weeks had 7.8 mg/dL lower total cholesterol and 7.3 mg/dL lower LDL cholesterol concentrations than those treated with placebo ⁸³. In subgroup analyses, the benefits of probiotics were slightly greater in studies that lasted 8 weeks or longer and in participants who had baseline cholesterol levels higher than 240 mg/dL. Among the strains included in more than three studies, Lactobacillus acidophilus, a mixture of Lactobacillus acidophilus and Bifidobacterium lactis, and Lactobacillus plantarum were associated with significant reductions in total and LDL cholesterol concentrations, but Lactobacillus helveticus and Enterococcus faecium were not. In a smaller meta-analysis of 11 randomized controlled trials in 602 adults with normal or high cholesterol levels, those treated with probiotics for 2 to 10 weeks had 6.6 mg/dL lower total cholesterol and 8.5 mg/dL lower LDL cholesterol levels than those treated with placebo, but the probiotic treatment had no significant effects on HDL cholesterol levels ⁸⁴. The effects were most pronounced with consumption of probiotics for more than 4 weeks by participants with hypercholesterolemia and those aged 45 or older. In both meta-analyses, participants included both healthy adults and adults with hypercholesterolemia, cardiovascular disease, diabetes, or obesity.

However, the authors of a more recent review of the influence of probiotics on blood lipid profiles of healthy adults (in 14 studies with a total of 942 adults treated from 15–150 days) found insufficient evidence to conclude that probiotics improve blood lipid levels ⁸⁵. Another review found that use of probiotics containing multiple strains produced statistically significant reductions in total and LDL cholesterol levels (by 12.0 and 20.1 mg/dL, respectively), whereas trials that used a single strain did not ⁸⁶.

Overall, research suggests that the use of multiple probiotic strains in combination as well as of probiotics containing Lactobacillus acidophilus, a mixture of Lactobacillus acidophilus and Bifidobacterium lactis, or Lactobacillus plantarum might reduce total and LDL cholesterol levels. However, more research is needed to confirm these findings.

Probiotics for the treatment of bacterial vaginosis

Bacterial vaginosis is one of the most common causes of genital discomfort in women of reproductive age. This condition occurs when there is an imbalance in the population of normal vaginal micro-organism with depletion of the dominant lactobacilli and overgrowth of other types of bacteria. Treatment of this condition using recommended antibiotics is often associated with failure and high rates of recurrence. This led to the concept of replacing the depleted lactobacilli using probiotic strains as a treatment approach. This review investigated the evidence for the use of probiotic preparations either alone or in conjunction with antibiotics for the treatment of bacterial vaginosis. The current research ⁸⁷ does not provide conclusive evidence that probiotics are superior to or enhance the effectiveness of antibiotics in the treatment of bacterial vaginosis. In addition, there is insufficient evidence to recommend the use of probiotics either before, during or after antibiotic treatment as a means of ensuring successful treatment or reduce recurrence.

Probiotics for people with hepatic encephalopathy

Hepatic encephalopathy is a disorder of brain function as a result of liver failure or portosystemic shunt or both. Both hepatic encephalopathy (clinically overt) and minimal hepatic encephalopathy (not clinically overt) significantly impair patient’s quality of life and daily functioning and represent a significant burden on healthcare resources. Prebiotics such as lactulose are commonly used for the prevention and treatment of hepatic encephalopathy. Evidence for one probiotic mixture suggests that it can reverse minimal hepatic encephalopathy. Of the 21 included trials including 1420 participants, 14 trials compared a probiotic with placebo or no treatment and seven trials compared a probiotic with lactulose. The treatment duration of the trials ranged from 10 days to 180 days.

Compared with placebo or no intervention, probiotics probably improve recovery and may lead to improvements in the development of overt hepatic encephalopathy, quality of life, and plasma ammonia concentrations, but probiotics may lead to little or no difference in mortality. Whether probiotics are better than lactulose for hepatic encephalopathy is uncertain because the quality of the available evidence was very low. High-quality randomised clinical trials with standardised outcome collection and data reporting are needed to further clarify the true efficacy of probiotics ⁸⁸.

Probiotics in infants for prevention of allergic disease and food hypersensitivity

Reactions to foods and allergies (including asthma, eczema and hay fever) are common and may be increasing in developed countries. Many infants become sensitised to foods, including infant formula, through their gastrointestinal tract, a process that may be affected by the composition of the intestinal bacteria.

There is insufficient evidence to recommend the addition of probiotics to infant feeds for prevention of allergic disease or food reactions ⁸⁹.

Probiotics for maintenance of remission in ulcerative colitis

Ulcerative colitis is a chronic relapsing inflammatory disorder of the large bowel. Probiotics are living microorganisms that are thought to alter the growth of bacteria in the bowel and reduce inflammation. These reviews ⁹⁰,  ⁹¹ investigated the evidence for the use of probiotics for the maintenance of remission in ulcerative colitis. Four studies were identified which tested the effect of probiotics among 587 patients with ulcerative colitis in remission. The studies ranged in length from 3 to 12 months. The studies did not find any benefit for probiotic treatment compared to either placebo (pills not containing probiotics) or conventional treatment using mesalazine (a 5-ASA drug taken by mouth). Furthermore, conventional therapy combined with a probiotic did not improve overall remission rates in patients with mild to moderate ulcerative colitis. Probiotic treatment was generally well tolerated but the number of side effects reported was similar to that reported with mesalazine. Common side effects included diarrhoea, mucous secretion, bloody stools, abdominal pain, flatulence and distension, nausea and vomiting and headache. Whether probiotics are effective in patients with severe and more extensive disease and whether they can be used as an alternative to existing therapies is unknown. Further well designed, larger randomised controlled trials are needed to determine whether probiotics can be used as an alternative to current treatment modalities ⁹¹.

Probiotics for treatment of active Crohn’s disease and for maintenance of remission in Crohn’s disease

Crohn’s disease causes chronic inflammation of the intestines, which has periods of inactivity and periods when it flares up. Crohn’s disease can affect any part of the digestive tract, from the mouth to the anus. The most common symptoms of Crohn’s disease are abdominal pain, and diarrhoea. Probiotics are living microorganisms that are thought to benefit health by altering the growth and activity of bacteria in the intestines thereby reducing inflammation.

For Crohn’s disease active treatment, only one study was identified and this did not show that probiotics had any effect in treating active Crohn’s disease ⁹². However this study was only small (11 patients) and no definite conclusion can be made regarding the effectiveness of probiotics. Probiotics were generally well tolerated and no side effects were reported. There is insufficient evidence to make any conclusions about the effectiveness of probiotics for treatment of active Crohn’s disease.

For Crohn’s disease maintenance treatment, seven small studies of variable quality were reviewed. The studies tested the effect of maintenance treatment with probiotics (e.g. Lactobacilli GG, Escherichia coli strain Nissle 1917, VSL#3, Saccharomyces boulardii) among patients with Crohn’s disease in remission. Remission was induced by medical or surgical treatment. The studies lasted for 6 months to a year. The studies did not demonstrate any benefit for probiotic treatment for the maintenance of remission in Crohn’s disease ⁹³. Therefore, currently, there is no evidence to support the use of probiotics for the maintenance treatment of Crohn’s disease.

Probiotics Dosage

The dose needed for probiotics varies greatly depending on the strain and product. Although many over-the-counter products deliver in the range of 1–10 billion colony-forming units (CFU)/dose, some products have been shown to be efficacious at lower levels, while some require substantially more. It is not possible to state a general dose that is needed for probiotics; the dosage should be based on human studies showing a health benefit.

Because probiotics are alive, they are susceptible to die-off during product storage. Responsible manufacturers build in overages so that at the end of the product’s shelf-life, it does not fall below the potency declared on the label. Spore-forming probiotic strains, although not as well studied as others, do have the advantage of superior resistance to environmental stress during shelf-life. Probiotic products on the market have been shown in some cases to fail to meet label claims regarding the numbers and types of viable microbes present in the product.

The quality of probiotic products depends on the manufacturer concerned. Since most are not made to pharmaceutical standards, the regulatory authorities may not oversee adherence to quality standards. The issues that are important specifically for probiotic quality include maintenance of viability (as indicated by colony-forming units, or CFU) through the end of the product’s shelf-life and using the current nomenclature to identify the genus, species, and strain of all organisms included in the product.

Safety and Side Effects of Probiotics

Probiotics, such as strains of Lactobacillus, Bifidobacterium, and Propionibacterium, have a long history of use in food and are often present in the normal gastrointestinal microbiota, indicating that Lactobacillus, Bifidobacterium, and Propionibacterium probiotic supplements are safe for most people ⁹⁴. Whether probiotics are likely to be safe for you depends on the state of your health ⁹⁵. Studies suggest that probiotics usually have few side effects. However, the data on safety, particularly long-term safety, are limited, and the risk of serious side effects may be greater in people who have underlying health conditions.

• In people who are generally healthy, probiotics have a good safety record. Side effects, if they occur at all, usually consist only of mild digestive symptoms such as gas ¹³.
• On the other hand, there have been reports linking probiotics to severe side effects, such as dangerous infections, in people with serious underlying medical problems. The people who are most at risk of severe side effects include critically ill patients, those who have had surgery, very sick infants, and people with weakened immune systems ⁹⁴. For example, in a few cases (mainly in individuals who were severely ill or immunocompromised), the use of probiotics was linked to bacteremia, fungemia (fungi in the blood), or infections that resulted in severe illness ¹⁹.
• Probiotic products may contain different types of probiotic live microorganisms and have different effects in the human body. The effects also may vary from person to person.

Even for healthy people, there are uncertainties about the safety of probiotics. Because many research studies on probiotics haven’t looked closely at safety, there isn’t enough information right now to answer some safety questions. Most of our knowledge about safety comes from studies of Lactobacillus and Bifidobacterium; less is known about other probiotics ⁹⁵. Information on the long-term safety of probiotics is limited, and safety may differ from one type of probiotic to another. For example, even though a National Center for Complementary and Integrative Health – funded study showed that a particular kind of Lactobacillus appears safe in healthy adults age 65 and older, this does not mean that all probiotics would necessarily be safe for people in this age group.

The National Institutes of Health has established the Human Microbiome Project to study the many microorganisms and their genes (called the “microbiome”) that share our body space. These microbes outnumber our own cells by 10 to 1 and one of the most important things they do for us is to help with digestion. Part of this project is an initiative to study probiotic products, including their health benefits, how they work, and their long-term effects ⁹⁵.

Don’t replace scientifically proven treatments with unproven products and practices. Don’t use a complementary health product, such as probiotics, as a reason to postpone seeing your health care provider about any health problem.

If you’re considering a probiotic dietary supplement, consult your health care provider first. This is especially important if you have health problems. Anyone with a serious underlying health condition should be monitored closely while taking probiotics.

If you’re pregnant or nursing a child, or if you’re considering giving a child a dietary supplement, such as probiotics, it’s especially important to consult your (or your child’s) health care provider.

Tell all your health care providers about any complementary or integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

Where Do You Find Probiotics?

Fermented or cultured dairy products are a major source of probiotics ⁹⁶. Other sources of probiotics include:

• miso
• tempeh
• soy beverages
• buttermilk
• fermented milk.

The bacteria either occur naturally in these foods or have been added during preparation. Probiotics are also available as dietary supplements in capsule, tablet or powder-form.

Here are the most common strains of probiotics:

• Lactobacillus acidophilus
• Lactobacillus bulgaricus
• Lactobacillus casei
• Lactobacillus gasseri
• Lactobacillus plantarum
• Bifidobacterium bifidum
• Bifidobacterium lactis
• Bifidobacterium longum
• Enterococcus faecium
• Saccharomyces boulardii.

Bifidus regularis, a name created for marketing purposes by Dannon, is also known as Bifidobacterium animalis DN-173 010. This strain of probiotics is used exclusively in Dannon’s popular Activia products, which Dannon claims promote regularity.

Keep in mind that in order for a yogurt to be considered probiotic, it must contain one of the strains listed above. All yogurts are required to be treated with the strains Lactobacillus bulgaricus and Streptococcus thermophilus.

Food marketers have found a new niche with probiotic-containing foods, which include

• Probiotic cereal
• granola bars
• soy milk
• cottage cheese
• sour cream
• infant formula.

However, their claims may be based only on preliminary scientific findings.

More research is needed to see whether probiotic bacterias’ beneficial effects are the same when they’re treated or added to food products. Dried probiotics may survive a trip through the intestines if prepared and stored properly. Heat often kills live active cultures.

Probiotics Summary

Although some probiotics have shown promise in research studies, strong scientific evidence to support specific uses of probiotics for most health conditions is still lacking. And the probiotic strains in the supplements may not be specific for the condition you’re looking to treat. The U.S. Food and Drug Administration (FDA) has not approved any probiotics for preventing or treating any health problem. Some experts have cautioned that the rapid growth in marketing and use of probiotics may have outpaced scientific research for many of their proposed uses and benefits. The best we can say right now is taking probiotics as supplement won’t hurt and may help. And remember do not replace scientifically proven treatments with unproven products or practices. For basic information and research news about probiotics you can go to ⁹⁷.

References

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    Probiotics for Women to Prevent Gestational Diabetes Mellitus

    Gestational diabetes mellitus is a condition where the mother has high blood sugar levels during pregnancy. It is associated with a range of adverse pregnancy outcomes for the mother, such as pre-eclampsia (high blood pressure with protein in the urine) and instrumental or operative delivery, as well as for the infants who may be born large-for-gestational age, as a result, be injured at birth, or cause injury to their mothers during birth. Additionally, there can be long-term health problems for women and their babies, including an increased risk of cardiovascular disease or type 2 diabetes. The number of women being diagnosed with GDM is increasing around the world, so finding simple and cost-effective ways to prevent women developing gestational diabetes mellitus is important ((Cochrane Review 3 January 2017. Dietary advice during pregnancy to prevent gestational diabetes. http://www.cochrane.org/CD006674/PREG_dietary-advice-during-pregnancy-prevent-gestational-diabetes

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