- What is protein
- What are amino acids?
- What is the function of protein?
- Protein and health
- Best protein powder for weight loss
What is protein
Proteins are nitrogen-containing substances that are formed by amino acids. Protein is present in many foods that you eat. Protein can be found in foods from animals and from plants. The typical diet in the United States contains 14–16% of total energy intake as protein 1). Proteins serve as the major building blocks of muscle and other tissues in your body. Proteins build and help to maintain and repair muscles, organs, and other parts of your body. In addition, proteins are used to produce hormones, enzymes, hemoglobin that carries oxygen in your blood and initiators of cellular death. At least 10,000 different proteins make you what you are and keep you that way. Proteins can also be used as energy; however, they are not the primary choice as an energy source. For proteins to be used by your body they need to be metabolized into their simplest form, amino acids. Protein is made from twenty-plus basic building blocks called amino acids. There have been 20 amino acids identified that are needed for human growth and metabolism. Twelve of these amino acids (eleven in children) are termed nonessential, meaning that they can be synthesized by your body and do not need to be consumed in your diet. The remaining amino acids cannot be synthesized in your body and are described as essential amino acids meaning that they need to be consumed in your diets. The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine, must come from food. The absence of any of these amino acids will compromise the ability of your tissue to grow, be repaired or be maintained.
Protein is a vital part of the human diet and is present in various foods, like eggs, meats, dairy, seafood legumes, nuts, and seeds. Irrespective of the source of the protein consumed, it gets broken down in reformed into new proteins in your body. These proteins do everything from fighting infections to helping cells divide. The L-isomer of each amino acid is usually the more biologically relevant form as compared to the D isomer. The Healthy Eating Plate encourages you to eat protein-rich foods like beans, nuts, tofu, fish, chicken, or eggs in place of less-healthy options like red and processed meats. For example, try a turkey or black bean burger instead of a traditional beef burger. Or slice up a fresh-roasted chicken breast or salmon for your sandwich instead of using processed high-sodium lunch meat.
Table 1. Protein types
|Complete Protein||A food source that provides all nine essential amino acids necessary for dietary needs.||Meat, Poultry, Fish, Milk, Eggs|
|Incomplete Protein||A food source that lacks one or more of the nine essential amino acids.||Nuts, seeds, whole grains, vegetables, legumes (beans)|
|Complementary Protein||Two or more incomplete proteins paired together to provide all essential amino acids creating a complete protein.||Beans and rice|
Peas and corn
Almonds and peanuts
Nut butter and whole grain toast
Footnote: Incomplete proteins, like those mentioned above, aren’t “bad” or useless, they just don’t provide all essential amino acids when eaten independently.
- Complete proteins are primarily found in animal sources such as meat, poultry, fish, dairy, pork and eggs. There are exceptions, like soy. When you eat these foods, you’re getting all of the essential amino acids the body needs to carry out the many jobs amino acids have in the body such as regulating body processes, enzymes and hormone function and building muscle tissue, to name a few.
- Incomplete protein are plant based proteins, which are usually limited in one or another amino acids. Beans, for example, are low in methionine. When combined with rice, which has more methionine but is instead lower in lysine, they complement one another and make a complete protein.
Muscle protein constantly undergoes synthesis and breakdown, and skeletal muscle mass is regulated by many signals 2), including exercise, physical tension, nutrients, hormones, and cytokines 3). Increased protein synthesis rather than the breakdown of muscle protein, causes increase muscle mass 4). After exercising in the fasting state, the net muscle protein balance becomes negative, whereas when protein is ingested after the exercise, the net muscle protein balance becomes positive 5). Therefore, many athletes use supplementary protein powder to gain skeletal muscle mass 6). No safety concerns reported at daily recommended intakes for athletes of up to about 2.0 g/kg body weight (e.g., 136 g for a person weighing 150 lb) 7).
A dysfunctional protein can lead to a variety of medical conditions and, often, death. Dysfunctional proteins can lead to childhood obesity, breakdown of the retina leading to blindness, hearing loss, and type 2 diabetes.
Take, for example, the protein cilia and how its dysfunction manifests:
- Inadequate cilia in flagella lead to sperm dysmotility.
- Defective cilia in the respiratory tract lead to chronic lung infections.
- Eustachian tube cilia dysfunction causes chronic ear infections and hearing loss.
- Dysfunctional cilia in Fallopian tubes cause infertility.
Many infective agents work by mimicking human accessory proteins and binding to elongation factors. Although the bacteria inhibit proteins, viruses actually “hijack” and use the host’s protein synthesis machinery for reproduction and further infection. Infectious, misfolded proteins called “prions,” short for “proteinaceous and infectious virions,” infect as a normally folded protein then replicate and misfold into β-sheets called an “amyloid fold.” These aggregate into amyloid plaques and create “holes” in tissue creating a “spongiform” appearance. Prions affect nervous tissue leading to harmful and deadly neurological symptoms 8).
Mutations that alter collagen’s structure promote frequent fractures, easy bruising, weak joints, and hearing loss due to abnormal inner ear bones 9).
A genetic disease can cause a deficiency of the enzyme required to convert amino acids into neurotransmitters and skin pigment. The disease does not result from the decrease in amino acid levels, rather from the high concentration of amino acids. This promotes activity in a minor enzymatic pathway producing toxic products. The presence of these products is screened for in the blood as part of standard neonatal testing. Patients usually express traits of albinism, white-blond hair, pale blue eyes, and an odor from the toxic products in their sweat, urine, skin, and hair. Treatment of this disease is with a diet low in specific amino acids 10).
Diseases in skeletal muscle proteins may cause a rapid breakdown, therefore resulting in the inability to walk 11).
Misfolded proteins can cause numerous, clinically significant diseases. Most notably is cystic fibrosis, an autosomal recessive disorder due to a defect in the chloride channel CFTR protein, which regulates water, chloride movement, and mucus production. Normally this protein is a channel for chloride to move out of cells to balance the tonicity of salt and water. Sodium is an ion that moves in a counter-current fashion to balance the osmolality between compartments. This is important in glandular tissues that secrete large concentrations of sodium chloride. Mucus plugs, recurrent infections, infertility, and gastrointestinal dysfunction are common manifestations 12).
Acute phase reactants caused mostly by interleukin-6 (IL-6) made by macrophages and also T-helper cells. Too many acute-phase proteins can be deposited anywhere in the body. The non-specific deposition is called amyloidosis. Deposition into the vasculature alters their integrity. Compliance with blood vessel walls will decrease, leading to less distensibility; this makes the blood vessel more likely to rupture if the pressure goes up—a massive intracerebral hemorrhage in a young person with no prior history of hypertension or trauma. Diagnostic confirmation is via congo red stain, which shows a characteristic apple-green birefringence 13).
Beta-amyloid or tau protein is present in both age-related and Down syndrome-related Alzheimer disease (beta-lipoprotein E4 is more specific for Alzheimer’s disease). In the general population, this protein gets oxidized, causing Alzheimer disease. Neurofibrillary tangles are the manifestation of the tau protein undergoing oxidation and aggregating. In Down syndrome, the body is not able to cleave the beta-lipoprotein from the amyloid precursor protein. The result is the build-up of beta lipoprotein, which causes early-onset Alzheimer disease.
How much protein do I need?
Research suggests people should aim for about 25% to 30% of their total calorie intake from protein. Protein is filling and is necessary to build and maintain muscle. Current data suggest that dietary protein intake necessary to support metabolic adaptation, repair, remodeling, and for protein turnover generally ranges from 1.2 to 2.0 gram per kilogram body weight per day 14). And this total intake should be balanced with quality carbs and quality fat. The National Academy of Medicine 15) recommends that adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day, or just over 7 grams for every 20 pounds of body weight.
- For a 140-pound person, that means about 50 grams of protein each day.
- For a 200-pound person, that means about 70 grams of protein each day.
The National Academy of Medicine also sets a wide range for acceptable protein intake anywhere from 10% to 35% of calories each day. Beyond that, there’s relatively little solid information on the ideal amount of protein in the diet or the healthiest target for calories contributed by protein. In an analysis conducted at Harvard Chan School of Public Health 16), among more than 130,000 men and women who were followed for up to 32 years, the percentage of calories from total protein intake was not related to overall mortality or to specific causes of death. However, the source of protein was important.
It’s important to note that millions of people worldwide, especially young children, don’t get enough protein due to food insecurity. The effects of protein deficiency and malnutrition range in severity from growth failure and loss of muscle mass to decreased immunity, weakening of the heart and respiratory system, and death. However, it’s uncommon for healthy adults in the U.S. and most other developed countries to have a deficiency, because there’s an abundance of plant and animal-based foods full of protein. In fact, many in the U.S. are consuming more than enough protein, especially from animal-based foods 17).
What are complete proteins and how much do I need?
“Pure” protein, whether derived from plant or animal foods, probably has similar effects on health, although the mix of amino acids can have health implications. Some proteins found in food are “complete”, meaning they contain all twenty-plus types of amino acids needed to make new protein in your body. Others are incomplete, lacking one or more of the nine essential amino acids, which your body can’t make from scratch or from other amino acids. Animal-based foods (meat, poultry, fish, eggs, and dairy foods) tend to be good sources of complete protein, while plant-based foods (fruits, vegetables, grains, nuts, and seeds) often lack one or more essential amino acid. Those who abstain from eating animal-based foods can eat a variety of protein-containing plant foods each day in order to get all the amino acids needed to make new protein, and also choose to incorporate complete plant proteins like quinoa and chia seeds.
Why is a complete protein better for the body as opposed to an incomplete protein?
Complete proteins offer all of the essential amino acids. Incomplete proteins do not, so they need to be combined with other proteins to get all of the essential amino acids (beans and rice, for example). Beans are low in methionine, while rice is low in lysine. Put them together and you have the essential amino acids that you need.
What are amino acids?
Amino acids are organic compounds that contain amino and carboxyl functional groups, along with a side chain specific to each amino acid that combine to form proteins. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, although other elements are found in the side chains of certain amino acids. Amino acids and proteins are the building blocks of life.
When proteins are digested or broken down, amino acids are left. The human body uses amino acids to make proteins to help the body:
- Break down food
- Repair body tissue
- Perform many other body functions
Amino acids can also be used as a source of energy by the body.
While there are hundreds of amino acids in nature, humans use only 20 of them. One way to further classify them is by defining which ones healthy bodies can and cannot make.
The three classes of proteins are:
- Non-Essential amino acids
- Conditionally Essential amino acids
- Essential amino acids
Non-Essential Amino Acids
There are five amino acids termed non-essential because they can be obtained from foods and also generated within your body.
The non-essential amino acids are:
- Aspartic acid
- Glutamic acid
Conditionally-Essential Amino Acids
There are six amino acids termed conditionally-essential because healthy bodies can generate them under normal physiologic conditions. They become essential under certain conditions like starvation or inborn errors of metabolism.
The conditionally essential amino acids are:
Essential Amino Acids
There are nine amino acids termed essential because they cannot be generated within your body. Dietary protein, therefore, provides these amino acids, which are needed to make certain hormones and other important molecules.
The essential amino acids are:
You do not need to eat essential and nonessential amino acids at every meal, but getting a balance of them over the whole day is important. A diet based on a single plant item will not be adequate, but you no longer worry about pairing proteins (such as beans with rice) at a single meal. Instead you look at the adequacy of the diet overall throughout the day.
In general, animal-based protein foods such as eggs, dairy, meat, and seafood provide all nine of the essential amino acids in adequate amounts 18). Soy-based foods are unique because they are tasteless and provide all nine essential amino acids in sufficient quantities. Most other plant foods, including whole grains, nuts, legumes, and seeds, possess high levels of some amino acids and low amounts of others. It would be wrong to assume that animal-based foods provide more protein than plant-based ones. A cup of tofu contains the same number of grams of protein as 3 ounces of steak, chicken, or fish 19). A half-cup of lentils has more grams of protein than an egg. Not all plant foods are low in the same amino acids, so eating a variety of plant-based foods can provide all nine of the essential amino acids. For example, pairing protein sources, like rice and beans or hummus and pita bread or oatmeal topped with almond butter. However, in terms of volume, it may be necessary to eat more plant-based foods to get a similar amount of protein and amino acid profile provided by animal-based proteins 20).
What is the function of protein?
Proteins serve crucial roles in human biochemistry. Proteins’ major role is to provide the body’s building blocks. Proteins are the precursors of several biologically relevant molecules. Therefore either the excess or deficiency of protein can lead to disease result in nervous system defects, metabolic problems, organ failure, and even death. Table 2 lists a variety of the functions of body proteins and amino acids. From the practical standpoint of human physiology, the major roles of body proteins are (1) those relating to protein synthesis and protein breakdown in the context of maintaining lean body mass, (2) efficient operation of regulatory proteins required for conduct and optimization of body functions, and (3) the energy costs of the above, including the cost of oxidation and excretion of protein metabolites resulting from the metabolic reactions constituting these events. The net physiological results that are useful to a human include increased strength, improved endurance, optimization of “fight or flight” reactions (preferably the former), efficient blood coagulation and wound healing, enhanced immunological functions with improved disease resistance, and peak mental alertness and memory.
Table 2. Some functions of amino acids and their products
|Substrates for protein synthesis||Those amino acids for which there is a codon|
|Regulators of protein turnover||Leucine, arginine?|
|Regulators of enzyme activity||Arginine and N-acetylglutamate synthetase Phenylalanine and phenylalanine hydroxylase activation|
|Precursor of signal transducer||Arginine and nitric oxide|
|Ion fluxes||Taurine, glutamate|
|Physiologic molecular precursors||Arginine, glutamine, purines|
|Nitrogen transporters||Alanine, glutamine|
|Circulating transporters||Ceruloplasmin; apolipoproteins Vitamin and hormone binding proteins|
|Messengers/Signals||Insulin, growth factors|
|Growth, differentiation, gene expression||Growth factors, transcription factors|
Enzymes proteins accelerate a reaction as a catalyst. Catalyzed reactions are one million or more times faster. Enzymes usually have the suffix “-ase” in their name. Exceptions are enzymes discovered before the start of the naming scheme. Each enzyme is regulated by competitive and noncompetitive inhibitors and/or by allosteric molecules. Enzymes can catalyze pathways to produce or break down biological molecules. Changes to enzymes can lead to disease or treatment. Specific amino acids form an enzyme’s substrate-binding site. A substrate-binding site is the “active site.” This serves in chemical reactions. Substrates can be hydrophobic, hydrophilic, charged, uncharged, neutral, or a combination. Mutations that change amino acids in the active site change the enzyme’s activity. A substrate will join an enzyme that is lined with compatible amino acids. If these amino acids change, a substrate may not be able to join, therefore rendering an enzyme non-functional. How a substrate interacts with an active site signifies the “affinity” of that enzyme. Greater affinity means fewer substrate is needed to achieve a reaction. A mutation that changes the active site can raise or lowers the affinity 22).
Proteins serve as the structural elements of cells and tissues—the proteins actin and tubulin form actin filaments and microtubules. In muscle, actin provides the “scaffolding” against which myosin can produce muscle contraction 23).
Motor proteins transport molecules inside a cell, provide movement of certain parts of individual cells involved in specialized function, generate larger-scale movements of fluids and semisolids such as the circulation of blood and movement of food through the digestive tract, and finally provide movement of the human body through their roles in skeletal muscles. Myosin is a protein with a hydrophobic tail, a head group that can attach and detach from actin filaments, and a “hinge” section, which moves the head group back and forth, resulting in movement 24).
Channels are essential for the transportation of nutrients into and out of cells and for nerve signals and the selective filtration of molecules in the kidneys. This is exemplified in how the mammalian cell has an intracellular potassium concentration of approximately 140 millimoles per cell and sodium of 5 to 15 millimoles. The extracellular environment has a potassium concentration of 5 moles and a sodium concentration of 145 millimoles. Potassium specific channels are responsible for regulating these concentrations in their respective compartments 25).
Protein and health
Available evidence indicates that it’s the source of protein or the protein “package”, rather than the amount of protein, that likely makes a difference for your health. The evidence-based takeaway is that eating healthy protein sources like beans, nuts, fish, or poultry in place of red meat and processed meat can lower the risk of several diseases and premature death. The bottom line is that protein is a key part of any diet. The average person needs about 7 grams of protein every day for every 20 pounds of body weight. Because protein is found in an abundance of foods, many people can easily meet this goal. However, not all protein “packages” are created equal. Because foods contain a lot more than protein, it’s important to pay attention to what else is coming with it.
Research conducted at the Harvard Chan School of Public Health 26) has found that eating even small amounts of red meat, especially processed red meat, on a regular basis is linked to an increased risk of heart disease and stroke, and the risk of dying from cardiovascular disease or any other cause. Conversely, replacing red and processed red meat with healthy protein sources such as beans, soy foods, nuts, fish, or poultry seems to reduce these risks. One of the reasons why plant sources of protein are related to lower risk of cardiovascular disease compared to protein from red meat and dairy is because of the different types of fat in these protein packages. Plant-based protein sources are more unsaturated, which lowers LDL cholesterol (low-density lipoprotein, sometimes called “bad” cholesterol), an established risk factor for heart disease. Also, plant sources contain no cholesterol. Other factors are likely to contribute to the lower risk, but this is a key factor.
One investigation followed 120,000 men and women in the Nurses’ Health Study and Health Professionals Follow-Up Study for more than two decades 27). For every additional 3-ounce serving of unprocessed red meat the study participants consumed each day, their risk of dying from cardiovascular disease increased by 13% 28).
- Processed red meat was even more strongly linked to dying from cardiovascular disease—and in smaller amounts: every additional 1.5 ounce serving of processed red meat consumed each day (equivalent to one hot dog or two strips of bacon) was linked to a 20% increase in the risk of cardiovascular disease death.
- Cutting back on red meat could save lives: the researchers estimated that if all the men and women in the study had reduced their total red and processed red meat intake to less than half a serving a day, one in ten cardiovascular disease deaths would have been prevented.
In another study of 43,000 men 29) that looked at both amount and sources of protein found that intake of total protein was minimally associated with heart disease risk, but intake of protein from red meat was associated with higher risk.
Another study 30), the first meta-analysis of randomized controlled trials looking at the health effects of red meat by substituting it for other specific types of foods found that diets that replaced red meat with healthy plant proteins led to decreases in risk factors for cardiovascular disease.
- The study included data from 36 randomized controlled trials involving 1,803 participants. The researchers compared people who ate diets with red meat with people who ate more of other types of foods (i.e. chicken, fish, carbohydrates, or plant proteins such as legumes, soy, or nuts), looking at blood concentrations of cholesterol, triglycerides, lipoproteins, and blood pressure—all risk factors for cardiovascular disease. The researchers found that when diets with red meat were compared with all other types of diets combined, there were no significant differences in total cholesterol, lipoproteins, or blood pressure, although diets higher in red meat did lead to higher triglyceride concentrations than the comparison diets 31). However, the researchers found that diets higher in high-quality plant protein sources such as legumes, soy, and nuts resulted in lower levels of both total and LDL (“bad”) cholesterol compared to diets with red meat.
In terms of the amount of protein consumed, there’s evidence that eating a relatively high-protein diet may be beneficial for the heart, as long as the protein comes from a healthy source.
- A 20-year prospective study 32) of over 80,000 women found that those who ate low-carbohydrate diets that were high in plant-based sources of fat and protein had a 30% lower risk of heart disease compared with women who ate high-carbohydrate, low-fat diets. However, eating a low-carbohydrate diet high in animal fat or protein did not offer such protection.
- Further evidence of the heart benefits of eating healthy protein in place of carbohydrate comes from a randomized trial known as the Optimal Macronutrient Intake Trial for Heart Health 33). A healthy diet that replaced some carbohydrate with healthy protein (or healthy fat) did a better job of lowering blood pressure and harmful low-density lipoprotein (LDL) cholesterol than a higher carbohydrate diet 34).
- Similarly, the “EcoAtkins” weight loss trial 35) compared a low-fat, high -carbohydrate, vegetarian diet to a low-carbohydrate vegan diet that was high in vegetable protein and fat. Though weight loss was similar on the two diets, study participants on the high protein diet saw improvements in blood lipids and blood pressure 36).
- Occasionally a study will generate headlines because it found the opposite result. For example, one study of Swedish women who ate low-carbohydrate, high-protein diets had higher rates of cardiovascular disease and death than those who ate lower-protein, higher-carbohydrate diets 37). But the study, which assessed the women’s diets only once and then followed them for 15 years, did not look at what types of carbohydrates or what sources of protein these women ate. That was important because most of the women’s protein came from animal sources.
The source of protein matters more than protein quantity when it comes to diabetes risk. Eating more red meat predicts a higher risk of type 2 diabetes, while consuming nuts, legumes, and poultry is related to lower risk. A 2011 study 38) found that people who ate diets high in red meat, especially processed red meat, had a higher risk of type 2 diabetes than those who rarely ate red or processed meat. For each additional serving a day of red meat or processed red meat that study participants ate, their risk of diabetes rose 12% and 32%, respectively 39). Investigators also found that replacing a serving of red meat with one serving of nuts, low-fat dairy products, or whole grains each day was associated with an estimated 16% to 35% lower risk of type 2 diabetes. A related study 40) also found that people who started eating more red meat than usual were had a 50% higher risk of developing type 2 diabetes during the next four years, and researchers also found that those who reduced red meat consumption had a 14% lower risk of type 2 diabetes over a 10-year follow-up period.
How meat is cooked may also affect type 2 diabetes risk. In a study 41) that tracked the health of over 289,000 men and women, researchers found that individuals who most frequently ate red meats and chicken cooked at high temperatures were 1.5 times more likely to develop type 2 diabetes, compared to those who ate the least. There was also an increased risk of weight gain and developing obesity in the frequent users of high-temperature cooking methods, which may have contributed to the development of diabetes. Of note, this research demonstrated that cooking methods might contribute to diabetes risk beyond the effects of meat consumption alone 42).
More evidence that the source of protein matters comes from a 20-year study 43) that looked at the relationship between low-carbohydrate diets and type 2 diabetes in women. Low-carbohydrate diets that were high in vegetable sources of fat and protein were associated with a lower risk of type 2 diabetes. But low-carbohydrate diets that were high in animal sources of protein or fat did not show this benefit 44).
For type 1 diabetes (formerly called juvenile or insulin-dependent diabetes), proteins found in cow’s milk have been implicated in the development of the disease in babies with a predisposition to the disease, but research remains inconclusive 45).
When it comes to cancer, once again, the source of protein seems to matter more than quantity. In the Nurse’s Health Study and the Health Professionals Follow-Up Study 46), every additional serving per day of red meat or processed red meat was associated with a 10% and 16% higher risk of cancer death, respectively. In October 2015, the World Health Organization’s International Agency for Research on Cancer (IARC) concluded that consumption of processed meat is “carcinogenic to humans,” and that consumption of red meat is “probably carcinogenic to humans” 47). The IARC Working Group (comprised of 22 scientists from ten countries) reached these conclusions from an evaluation of over 800 studies. Conclusions were primarily based on the evidence for colorectal cancer. Data also showed positive associations between processed meat consumption and stomach cancer, and between red meat consumption and pancreatic and prostate cancer 48).
A 2014 study 49) also found a link between high consumption of red meat during adolescence and premenopausal breast cancer, while higher intakes of poultry, nuts, and legumes were associated with lower risk. Using data on the health of 89,000 women (aged 24 to 43) followed over a 20-year period, researchers found a 22% higher risk of breast cancer in those who ate 1.5 servings of red meat per day while in high school, compared to those who only had one serving per week. Each additional daily serving of red meat seemed to increase the risk of breast cancer by another 13% 50). How meat is cooked may also have implications for cancer risk. High-temperature grilling creates potentially cancer-causing compounds in meat, including polycyclic aromatic hydrocarbons and heterocyclic amines.
In 2016, researchers reviewed protein intakes of more than 131,000 women and men from the Nurses’ Health Study and Health Professionals Follow-up Study 51). After tracking their diets for up to 32 years, the authors found that a higher intake of red meat, especially processed versions (sausage, bacon, hot dogs, salami), was linked to a modestly higher risk of death, while a higher protein intake from plant foods carried a lower risk 52).
Digesting protein releases acids into the bloodstream, which the body usually neutralizes with calcium and other buffering agents. As a result, early research theorized that eating lots of protein requires a lot more calcium – which may be pulled from bone. A 2009 systematic review found that this doesn’t appear to happen 53).
Protein and weight loss
High protein diets can promote weight loss via increased insulin sensitivity, increased oxidation of fatty acids, increase appetite suppression and increase satiety. However, caution is necessary for people with diabetes who have gout because protein can elevate niacin levels, which may exacerbate gout related symptoms. For most healthy people, a high-protein diet generally isn’t harmful, particularly when followed for a short time. Such diets may help with weight loss by making you feel fuller. However, the risks of using a high-protein diet with carbohydrate restriction for the long term are still being studied. Several health problems may result if a high-protein diet is followed for an extended time:
- Some high-protein diets restrict carbohydrate intake so much that they can result in nutritional deficiencies or insufficient fiber, which can cause problems such as bad breath, headache and constipation.
- Some high-protein diets include foods such as red meat and full-fat dairy products, which may increase your risk of heart disease.
- A high-protein diet may worsen kidney function in people with kidney disease because your body may have trouble eliminating all the waste products of protein metabolism.
If you want to follow a high-protein diet, choose your protein wisely. Available evidence indicates that it’s the source of protein or the protein “package”, rather than the amount of protein, that likely makes a difference for your health. Good choices include soy protein, beans, nuts, fish, skinless poultry, lean beef, pork and low-fat dairy products. Avoid processed meats. The evidence-based takeaway is that eating healthy protein sources like beans, nuts, fish, or poultry in place of red meat and processed meat can lower the risk of several diseases and premature death. The bottom line is that protein is a key part of any diet. The average person needs about 7 grams of protein every day for every 20 pounds of body weight. Because protein is found in an abundance of foods, many people can easily meet this goal. However, not all protein “packages” are created equal. Because foods contain a lot more than protein, it’s important to pay attention to what else is coming with it.
Some proteins found in food are “complete”, meaning they contain all twenty-plus types of amino acids needed to make new protein in your body. Others are incomplete, lacking one or more of the nine essential amino acids, which your body can’t make from scratch or from other amino acids. Animal-based foods (meat, poultry, fish, eggs, and dairy foods) tend to be good sources of complete protein, while plant-based foods (fruits, vegetables, grains, nuts, and seeds) often lack one or more essential amino acid. Those who abstain from eating animal-based foods can eat a variety of protein-containing plant foods each day in order to get all the amino acids needed to make new protein, and also choose to incorporate complete plant proteins like quinoa and chia seeds. Building off this general guidance, here are some additional details and tips for managing your diet with the best protein choices:
- Get your protein from plants when possible. Eating legumes (beans and peas), nuts, seeds, whole grains, and other plant-based sources of protein is a win for your health and the health of the planet. If most of your protein comes from plants, make sure that you mix up your sources so no “essential” components of protein are missing. The good news is that the plant kingdom offers plenty of options to mix and match. Here are some examples for each category:
- Legumes: lentils, beans (adzuki, black, fava, chickpeas/garbanzo, kidney, lima, mung, pinto etc.), peas (green, snow, snap, split, etc.), edamame/soybeans (and products made from soy: tofu, tempeh, etc.), peanuts.
- Nuts and Seeds: almonds, pistachios, cashews, walnuts, hazelnuts, pecans, hemp seeds, squash and pumpkin seeds, sunflower seeds, flax seeds, sesame seeds, chia seeds.
- Whole Grains: kamut, teff, wheat, quinoa, rice, wild rice, millet, oats, buckwheat,
- Other: while many vegetables and fruits contain some level of protein, it’s generally in smaller amounts than the other plant-based foods. Some examples with higher protein quantities include corn, broccoli, asparagus, brussels sprouts, and artichokes.
- Upgrade your sources of animal protein. Considering the “protein package” is particularly important when it comes to animal-based foods:
- Generally, poultry (chicken, turkey, duck) and a variety of seafood (fish, crustaceans, mollusks) are your best bet. Eggs can be a good choice, too.
- If you enjoy dairy foods, it’s best to do so in moderation (think closer to 1-2 servings a day; and incorporating yogurt is probably a better choice than getting all your servings from milk or cheese).
- Red meat—which includes unprocessed beef, pork, lamb, veal, mutton, and goat meat—should be consumed on a more limited basis. If you enjoy red meat, consider eating it in small amounts or only on special occasions.
- Processed meats, such as bacon, hot dogs, sausages, and cold cuts should be avoided. Although these products are often made from red meats, processed meats also include items like turkey bacon, chicken sausage, and deli-sliced chicken and ham. Processed meat refers to any meat that has been “transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation” 54).
Researchers at the Harvard Chan School of Public Health 55) followed the diet and lifestyle habits of over 120,000 men and women for up to 20 years, looking at how small changes contributed to weight gain over time. Those who ate more red and processed meat over the course of the study gained more weight, about one extra pound every four years, while those who ate more nuts over the course of the study gained less weight, about a half pound less every four years 56). A subsequent detailed analysis of this cohort also found that eating red meat, chicken with skin, and regular cheese was associated with greater weight gain 57). Yogurt, peanut butter, walnuts and other nuts, chicken without skin, low-fat cheese, and seafood was associated with less weight gain 58).
Another study showed that eating around one daily serving of beans, chickpeas, lentils or peas can increase fullness, which may lead to better weight management and weight loss 59).
The quality of the carbohydrates (carbs) you eat is important too. Cut processed carbs from your diet and choose carbs that are high in fiber and nutrient-dense, such as whole grains and vegetables and fruit.
Though some studies show benefits of high-protein, low-carbohydrate diets in the short term (such as the paleo diet), avoiding fruits and whole grains means missing out on healthful fiber, vitamins, minerals, and other phytonutrients. It’s always a good idea to talk with your doctor or dietitian before starting a weight-loss diet. And that’s especially important in this case if you have kidney disease, diabetes or other chronic health condition.
Finally, keep in mind that weight loss may be temporary, especially if you return to your previous way of eating. The best eating plan is one that you can stick to long-term.
Best protein powder for weight loss
Protein powder is a popular nutritional supplement. Using protein powder may also aid weight loss and help people tone their muscles. There are many different types of protein powder, including dairy-based and plant-based powders. Dairy proteins seem to be superior to other proteins largely due to leucine content and the digestion and absorptive kinetics of branched-chain amino acids in fluid-based dairy foods 60). Dairy proteins are a complete source of all amino acids in the right proportion to provide optimal nutritional benefit to the consumer. High-quality dietary proteins are effective for the maintenance, repair, and synthesis of skeletal muscle proteins 61). The two most abundant dairy proteins are casein and whey. Casein is the primary constituent of milk, used to make cheese, while whey is most often made into yogurt or spray-dried for use in nutritional supplements, among other products 62). Whey is a homogenous mixture of many proteins, comprised of 63–50% beta-lactoglobulin, 20% alpha-lactalbumin, 8–6% bovine serum albumin, and 1% immunoglobulin G 63). Each whey protein contains all of the essential amino acids, which makes them valuable ingredients in protein powder formulations, but not all protein sources are created equal, with milk, eggs, and legumes emerging as natural sources of premium protein for dietary supplements. Soy protein is an excellent alternative to whey or casein for people who do not consume dairy. It also contains all the essential amino acids. Currently, nutritional protein powder is mainly made of soy protein isolate or whey protein 64). A 2013 review 65) found that long-term excessive consumption of protein may damage the kidneys and liver and affect the body’s bone and calcium balance. Excessively high levels of protein in the diet can also result in a reduced intake of other beneficial foods, such as fiber-rich fruits, vegetables, and legumes that the body uses to feed and sustain gut bacteria.
According to a 2020 study 66), many of the best-selling protein powders contain heavy metals such as arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb). In 2010, the US Consumer Reports measured heavy metal concentrations in 15 commercially available protein powder supplements, and reported that all of the examined products contained “detectable concentrations” of at least one heavy metal 67). In a separate evaluation in 2018 68), the Clean Label Project tested 133 protein powder supplements, and found that all of the tested products similarly contained “detectable concentrations” of heavy metals. Specifically, the Clean Label Project reported that 70 % and 74 % of the test products contained “measurable levels” of lead and cadmium, respectively 69). When ingested in sufficient quantities, arsenic, cadmium, mercury, and lead have been associated with adverse human health effects, potentially including carcinogenesis, neurotoxicity, nephrotoxicity and reproductive issues 70). For example, chronic exposure to cadmium is associated with renal disease, thyroid disruption, and weakened bones, while chronic exposure to arsenic is associated with dermal lesions and carcinogenic effects 71). Additionally, high doses of ingested lead compete with calcium in the body, affecting neurotransmitter release and heme synthesis, which may result in nervous, hematological, reproductive, and renal effects 72). Furthermore, sufficient mercury exposure can elicit neurological, motor, renal, cardiovascular, immune and reproductive dysfunction 73).
However, in order to lose weight, your energy expenditures must exceed energy intake. The amount of energy or calories you get from food and drinks (energy IN) is balanced with the energy your body uses for things like breathing, digesting, and being physically active (energy OUT):
- The same amount of energy IN and energy OUT over time = weight stays the same (Energy Balance)
- More energy IN than OUT over time = Weight Gain
- More energy OUT than IN over time = Weight Loss
To lose weight, most people need to reduce the number of calories they get from food and beverages (energy IN) and increase their physical activity (energy OUT). To achieve this imbalance, you can decrease energy intake, increase energy expenditures or combine a decrease in intake with an increase in expenditures. Being physically active and eating fewer calories will help you lose weight and keep the weight off over time. As a result, most weight loss recommendations advise combining a low caloric diet with an exercise program in order to achieve a significant energy deficit 74). A long-standing consistent observation is that regular exercise by itself is prescribed in small to moderate amounts resulting in modest weight loss or in some cases weight gain 75).
For a weight loss of 1–1 ½ pounds per week, daily intake should be reduced by 500 to 750 calories. In general 76):
- Eating plans that contain 1,200–1,500 calories each day will help most women lose weight safely.
- Eating plans that contain 1,500–1,800 calories each day are suitable for men and for women who weigh more or who exercise regularly.
Very low calorie diets of fewer than 800 calories per day should not be used unless you are being monitored by your doctor.
Energy balance is also important for maintaining a healthy weight. To maintain a healthy weight, your energy IN and OUT don’t have to balance exactly every day. It’s the balance over time that helps you maintain a healthy weight.
You can reach and maintain a healthy weight if you:
- Follow a healthy diet, and if you are overweight or obese, reduce your daily intake by 500 calories for weight loss
- Are physically active
- Limit the time you spend being physically inactive
While people vary quite a bit in the amount of physical activity (exercise) they need for weight control, many can maintain their weight by doing 150 to 300 minutes (2 ½ to 5 hours) a week of moderate-intensity activity such as brisk walking. People who want to lose a large amount of weight (more than 5 percent of their body weight) and people who want to keep off the weight that they’ve lost may need to be physically active for more than 300 minutes of moderate-intensity activity each week.
American College of Sports Medicine recommendations for physical activity for Weight Loss and Prevention of Weight Regain for Adults 77):
- Maintain and improving health: 150 minutes/week
- Prevention of weight gain: 150 – 250 minutes/week
- Promote clinically significant weight loss: 225 – 420 minutes/week
- Prevention of weight gain after weight loss: 200 – 300 minutes/week.
Whey is a general term that typically denotes the translucent liquid part of milk that remains following the process (coagulation and curd removal) of cheese manufacturing 78). From this liquid, whey proteins are separated and purified using various techniques yielding different concentrations of whey proteins. Whey is one of the two major protein groups of bovine milk, accounting for 20% of the milk while casein accounts for the remainder. Whey is a complete protein whose biologically active components provide additional benefits to enhance human function. All of the constituents of whey protein provide high levels of the essential amino acids and branched chain amino acids (BCAAs) that are important for their role in the maintenance of tissue and prevention of catabolic actions during exercise 79). Whey protein contains an ample supply of the amino acid cysteine. Cysteine appears to enhance glutathione levels, which has been shown to have strong antioxidant properties that can assist the body in combating various diseases 80). Whey protein also contains a number of other proteins that positively effect immune function such as antimicrobial activity 81). Additionally, whey is also rich in vitamins and minerals. Whey protein is most recognized for its applicability in sports nutrition. Additionally, whey products are also evident in baked goods, salad dressings, emulsifiers, infant formulas, and medical nutritional formulas.
There are three main forms of whey protein that result from various processing techniques used to separate whey protein. They are whey powder, whey concentrate, and whey isolate. Table 3 provides the composition of whey proteins.
Table 3. Composition (%) of whey protein forms
|Component||Whey Powder||Whey Concentrate||Whey Isolate|
|Protein||11 – 14.5||25 – 89||90|
|Lactose||63 – 75||10 – 55||0.5|
|Milk Fat||1 – 1.5||2 – 10||0.5|
Whey protein powder
Whey protein powder has many applications throughout the food industry. As an additive it is seen in food products for beef, dairy, bakery, confectionery, and snack products. Whey powder itself has several different varieties including sweet whey, acid whey (seen in salad dressings), demineralized (seen primarily as a food additive including infant formulas), and reduced forms. The demineralized and reduced forms are used in products other than sports supplements.
Whey protein concentrate
The processing of whey concentrate removes the water, lactose, ash, and some minerals. In addition, compared to whey isolates whey concentrate typically contains more biologically active components and proteins that make them a very attractive supplement for the athlete.
Whey protein isolate
Isolates are the purest protein source available. Whey protein isolates contain protein concentrations of 90% or higher. During the processing of whey protein isolate there is a significant removal of fat and lactose. As a result, individuals who are lactose-intolerant can often safely take these products 83). Although the concentration of protein in this form of whey protein is the highest, it often contain proteins that have become denatured due to the manufacturing process. The denaturation of proteins involves breaking down their structure and losing peptide bonds and reducing the effectiveness of the protein.
Casein is the major component of protein found in bovine milk accounting for nearly 70-80% of its total protein and is responsible for the white color of milk 84). Casein is the most commonly used milk protein in the industry today. Milk proteins are of significant physiological importance to the body for functions relating to the uptake of nutrients and vitamins and they are a source of biologically active peptides. Similar to whey protein, casein is a complete protein and also contains the minerals calcium and phosphorous. Casein has a protein digestibility corrected amino acid score (PDCAAS) rating of 1.23 (generally reported as a truncated value of 1.0) 85).
Casein exists in milk in the form of a micelle, which is a large colloidal particle. An attractive property of the casein micelle is its ability to form a gel or clot in the stomach. The ability to form this clot makes it very efficient in nutrient supply. The clot is able to provide a sustained slow release of amino acids into the blood stream, sometimes lasting for several hours (Boirie et al. 1997). This provides better nitrogen retention and utilization by the body.
Soy also known as soybean or Glycine max, is the most widely used vegetable protein source. The soybean, from the legume family, was first chronicled in China in the year 2838 B.C. and was considered to be as valuable as wheat, barley, and rice as a nutritional staple. Soy’s popularity spanned several other countries, but did not gain notoriety for its nutritional value in The United States until the 1920s. The American population consumes a relatively low intake of soy protein (5g per day) compared to Asian countries 86). Although cultural differences may be partly responsible, the low protein quality rating from the protein efficiency ratio (PER) scale may also have influenced protein consumption tendencies. However, when the more accurate protein digestibility corrected amino acid score (PDCAAS) scale is used, soy protein was reported to be equivalent to animal protein with a score of 1.0, the highest possible rating 87). Soy’s quality makes it a very attractive alternative for those seeking non-animal sources of protein in their diet and those who are lactose intolerant. Soy is a complete protein with a high concentration of branched chain amino acids (BCAAs). There have been many reported benefits related to soy proteins relating to health and performance (including reducing plasma lipid profiles, increasing LDL-cholesterol oxidation and reducing blood pressure), however further research still needs to be performed on these claims.
The soybean can be separated into three distinct categories; flour, concentrates, and isolates. Soy flour can be further divided into natural or full-fat (contains natural oils), defatted (oils removed), and lecithinated (lecithin added) forms 88). Of the three different categories of soy protein products, soy flour is the least refined form. It is commonly found in baked goods. Another product of soy flour is called textured soy flour. This is primarily used for processing as a meat extender.
Soy concentrate was developed in the late 1960s and early 1970s and is made from defatted soybeans. While retaining most of the bean’s protein content, concentrates do not contain as much soluble carbohydrates as flour, making it more palatable. Soy concentrate has a high digestibility and is found in nutrition bars, cereals, and yogurts.
Soy isolates are the most refined soy protein product containing the greatest concentration of protein, but unlike flour and concentrates, contain no dietary fiber. Soy isolates originated around the 1950s in The United States. They are very digestible and easily introduced into foods such as sports drinks and health beverages as well as infant formulas.
Table 4. Protein composition of soy flour, soy concentrates and soy isolates.
|Soy Protein Form||Protein Composition|
Soy health benefits
For centuries, soy has been part of a human diet. Epidemiologists were most likely the first to recognize soy’s benefits to overall health when considering populations with a high intake of soy. These populations shared lower incidences in certain cancers, decreased cardiac conditions, and improvements in menopausal symptoms and osteoporosis in women 89). Based upon a multitude of studies examining the health benefits of soy protein the American Heart Association issued a statement that recommended soy protein foods in a diet low in saturated fat and cholesterol to promote heart health 90). The health benefits associated with soy protein are related to the physiologically active components that are part of soy, such as protease inhibitors, phytosterols, saponins, and isoflavones 91). These components have been noted to demonstrate lipid-lowering effects, increase LDL-cholesterol oxidation, and have beneficial effects on lowering blood pressure.
Of the many active components in soy products, isoflavones have been given considerably more attention than others. Isoflavones are thought to be beneficial for cardiovascular health, possibly by lowering LDL concentrations 92) increasing LDL oxidation 93) and improving vessel elasticity 94). However, these studies have not met without conflicting results and further research is still warranted concerning the benefits of isoflavones.
Soy benefits for women
An additional focus of studies investigating soy supplementation has been on women’s health issues. It has been hypothesized that considering that isoflavones are considered phytoestrogens (exhibit estrogen- like effects and bind to estrogen receptors) they compete for estrogen receptor sites in breast tissue with endogenous estrogen, potentially reducing the risk for breast cancer risk 95). In some animal studies, rodents that were exposed to high doses of compounds found in soy called isoflavones showed an increased risk of breast cancer. This is thought to be because the isoflavones in soy can act like estrogen in the body, and increased estrogen has been linked to certain types of breast cancer. But rodents process soy differently from people, and the same results have not been seen in people. Also, doses of isoflavones in the animal studies are much higher than in humans. In fact, in human studies, the estrogen effects of soy seem to either have no effect at all, or to reduce breast cancer risk (especially in Asian countries, where lifelong intake is higher than the US). This may be because the isoflavones can actually block the more potent natural estrogens in the blood. Still, the association between soy intake and breast cancer risk remains inconclusive. So far, the evidence does not point to any dangers from eating soy in people, and the health benefits appear to outweigh any potential risk. In fact, there is growing evidence that eating traditional soy foods such as tofu, tempeh, edamame, miso, and soymilk may lower the risk of breast cancer, especially among Asian women. Soy foods are excellent sources of protein, especially when they replace other, less healthy foods such as animal fats and red or processed meats. Soy foods have been linked to lower rates of heart disease and may even help lower cholesterol. Oother studies have demonstrated positive effects of soy protein supplementation on maintaining bone mineral content 96) and reducing the severity of menopausal symptoms 97).
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