What is broccoli
Broccoli (Brassica oleracea var. italica) is an edible green plant in the cabbage family (family Brassicaceae, genus Brassica) large flowering head, stalk and small associated leaves are eaten as a vegetable. The word broccoli comes from the Italian plural of broccolo, which means “the flowering crest of a cabbage”, and is the diminutive form of brocco, meaning “small nail” or “sprout” 1). Broccoli is often boiled or steamed but may be eaten raw.
Broccoli is classified in the Italica cultivar group of the species Brassica oleracea. Broccoli has large flower heads, usually green in color, arranged in a tree-like structure branching out from a thick, edible stalk. The mass of flower heads is surrounded by leaves. Broccoli resembles cauliflower, which is a different cultivar group of the same species.
The most common large head and thick stalk variety, known as ‘Calabrese broccoli’, named after the place Calabria in Italy, although it is typically labeled simply as ‘broccoli’. There is another broccoli variety, with several thin stalks and heads, known as ‘sprouting broccoli’ or ‘Romanesco broccoli’ 2). A few other broccoli varieties, such as ‘broccolini’ or ‘baby broccoli’ – actually a hybrid of broccoli and kale, and ‘broccoflower’ – a cross between broccoli and cauliflower, are also quite common in the market as many people are fond of these vegetables 3).
Most of the researches reveal that broccoli is more nutritious, if it is eaten raw. Because raw broccoli provides significantly healthy dose of sulforaphane, a natural isothiocyanate thought to prevent cancer by helping to stimulate the body’s detoxifying enzymes, than cooked. Cooking locks sulforaphane in, making it unavailable to your body. Or, if one prefers it cooked, then steaming broccoli until it is cooked but still crunchy. Some research suggests this method may keep sulforaphane and other thermolabile components including some vitamins available 4).
The promotion of health by a diet that is rich in Brassica vegetables like broccoli, including its association with a decreased risk of cardiovascular disease:
- Lower risk of heart attack 5)
- Reduce risk of stroke 6)
- Cardiovascular disease risk reduction 7)
- Lowers LDL “bad” cholesterol 8) and
- Lower incidence in a wide variety of cancer types 9), including breast, lung 10), 11), prostate 12), and colorectal cancer 13), has been extensively reported in the literature. A diet of three to five servings per week is sufficient to decrease the risk of cancer development by ∼30%–40% 14).
Broccoli is a rich source of certain vitamins, minerals, and antioxidants which constitute its various beneficial roles over human health 15), 16). Studies reveal that people eating broccoli on a regular basis can manage blood sugar level and control type 2 diabetes than others 17). This is due to the presence of sulforaphane, the most abundant unique antioxidant found in all cruciferous vegetables including broccoli 18). In addition, dietary fibers as well as a phytochemical quercetin (an antioxidant), present in broccoli, may help to reduce blood sugar levels in people with diabetes. Broccoli may have some anti-inflammatory effects due to the presence of sulforaphane and another antioxidant kaempferol in sufficient amount 19). Both these phytochemicals are effective against chronic autoimmune conditions such as arthritis, type-1 diabetes, and allergies.
Dietary fibres of green vegetables like broccoli can help to prevent constipation, promote bowl movement, maintain a healthy digestive tract, and lower the risk of colorectal cancer. Moreover, broccoli is a no fat diet and hence it can control obesity and reduces the possibility of overweight.
A recent study 20) reveals that antioxidant such as sulforaphane and kaempferol prevent atherosclerosis in older person and thus lessen the risk of heart attack or stroke. Besides, high potassium content in broccoli has some positive impact on human health. This relaxes the blood vessels and lowers the risk of high blood pressure, which can lead to atherosclerosis and other cardiovascular problems. On the other hand, high sulforaphane content of broccoli protects persons with type-2 diabetes induced cardiomyopathy, a disease related to heart muscle that can cause high blood pressure and heart failure 21). Broccoli also improves bone health because high calcium and vitamin K work together to make strong bones and teeth.
Vitamin C or ascorbic acid in broccoli provides a range of benefits. High vitamin C content in broccoli helps the body in producing collagen, which is the main support system for body cells and organs, including the skin. As an antioxidant, vitamin C can also prevent skin damage, wrinkling due to aging and even skin cancer. In supplement form, it may also help to reduce the symptoms of the common cold and shorten the time a cold lasts.
Figure 1. Sulforaphane chemical structure
Broccoli nutrition facts
Fresh broccoli contains almost 90 per cent water, 7 per cent carbohydrates, 3 per cent protein and almost no fat (Table 1). The total carbohydrates content is very low, with sugars and dietary fibers are the main constituents. The sugars are fructose, glucose, sucrose, and small amounts of lactose and maltose. Broccoli is a fat free vegetable, containing total saturated fatty acids (0.079gm), monounsaturated fatty acids (0.040gm), and polyunsaturated fatty acids (0.170gm) in traces and no cholesterol at all. Broccoli is very low in calories, providing only 34 kcal per 100gm of fresh broccoli. Broccoli also has low content of protein and dietary fiber.
However, broccoli contains all the essential mineral nutrients as well as vitamins in sufficient amounts. One cup of fresh chopped broccoli contains about 43 milligrams (mg) of calcium (4.3 per cent of the recommended Daily Value or DV), 288 mg of potassium (6.1 per cent DV), 81 mg of vitamin C (90 per cent DV for men and more than 100 per cent DV for women), 92 micrograms of vitamin K (115 per cent DV), and 567 international units of vitamin A (about 11 per cent DV). Also a small amount of other vitamins, including thiamine, riboflavin, folate, vitamin E, and vitamin B6 are also present. In addition, broccoli is a rich source of some unique antioxidants (quercetin, sulforaphane and kaempferol) which can help to prevent the toxicity of free radicals or reactive oxygen during natural processes such as metabolism and environmental stresses.
Boiling broccoli reduces the levels of sulforaphane, with losses of 20–30% after five minutes, 40–50% after ten minutes, and 77% after thirty minutes. However, other preparation methods such as steaming, microwaving, and stir frying had no significant effect on the compounds 23).
Sulforaphane is a natural isothiocyanate derived from a glucosinolate found in cruciferous vegetables, especially broccoli 24). Sulforaphane has received a great deal of attention because of its ability to simultaneously modulate multiple cellular targets involved in cancer development, including 25):
- DNA protection by modulating carcinogen-metabolizing enzymes and blocking the action of mutagens;
- Inhibition of cell proliferation and induction of apoptosis, thereby retarding or eliminating clonal expansion of initiated, transformed, and/or neoplastic cells;
- Inhibition of neoangiogenesis, progression of benign tumors to malignant tumors, and metastasis formation.
Sulforaphane is therefore able to prevent, delay, or reverse preneoplastic lesions, as well as to act on cancer cells as a therapeutic agent. Taking into account this evidence and its favorable toxicological profile, sulforaphane can be viewed as a conceptually promising agent in cancer prevention and/or therapy. Sulforaphane is the hydrolysis product of glucoraphanin, particularly high in the young sprouts of broccoli and cauliflower. Sulforaphane can also be obtained by eating cruciferous vegetables such as brussel sprouts, broccoli, cauliflower, bok choy, kale, collards, arugula, broccoli sprouts, chinese broccoli, broccoli raab, kohlrabi, mustard, turnip, radish, watercress and cabbage 26).
Broccoli also contains the carotenoid compounds lutein and zeaxanthin in amounts about 6 times lower than in kale.
Table 1. Broccoli nutrition facts
|Nutrient||Unit||Value per 100 g||cup chopped 91 g||bunch 608 g||spear (about 5″ long) 31 g||stalk 151 g||cup, chopped or diced 44 g|
|Total lipid (fat)||g||0.37||0.34||2.25||0.11||0.56||0.16|
|Carbohydrate, by difference||g||6.64||6.04||40.37||2.06||10.03||2.92|
|Fiber, total dietary||g||2.6||2.4||15.8||0.8||3.9||1.1|
|Vitamin C, total ascorbic acid||mg||89.2||81.2||542.3||27.7||134.7||39.2|
|Vitamin A, RAE||µg||31||28||188||10||47||14|
|Vitamin A, IU||IU||623||567||3788||193||941||274|
|Vitamin E (alpha-tocopherol)||mg||0.78||0.71||4.74||0.24||1.18||0.34|
|Vitamin D (D2 + D3)||µg||0||0||0||0||0||0|
|Vitamin K (phylloquinone)||µg||101.6||92.5||617.7||31.5||153.4||44.7|
|Fatty acids, total saturated||g||0.039||0.035||0.237||0.012||0.059||0.017|
|Fatty acids, total monounsaturated||g||0.011||0.01||0.067||0.003||0.017||0.005|
|Fatty acids, total polyunsaturated||g||0.038||0.035||0.231||0.012||0.057||0.017|
|Fatty acids, total trans||g||0||0||0||0||0||0|
How to cook broccoli
Broccoli can be eaten raw, but blanching it quickly in boiling water helps give it a more crisp-tender texture and bring out its flavor. Broccoli can also be steamed, sautéed, and roasted. You could even throw long spears on the grill. To maintain the sulforaphane content of broccoli, it’s best broccoli are steamed for 4 to 5 minutes, until tender.
Because broccoli is so versatile, it can be eaten with just about anything. You can eat broccoli several times a week and prepare it differently each time. If someone is on a diet or watching calorie intake, he or she may add raw broccoli to salads. It also makes the perfect side dish. Sauté, steam, stir-fry or roast of broccoli for dinner, and eating it alongside meat or pairing it with another vegetable or rice or potatoes are very common practices in Indian cuisine.
Broccoli health benefits
Epidemiological studies have revealed a particular inverse correlation between the intake of cruciferous vegetables and colorectal cancer risk; one stronger than that between the latter and the intake of other vegetables 28). Cruciferous vegetables refer to those of the Brassicaceae family and include broccoli, cabbage, and Brussel sprouts. Particular to this plant family are glucosinolates—a group of compounds endogenously synthesised and derived from glucose and amino acid residues. Upon the rupture of plant cells—such as occurs from the consumption of the vegetables or from parasitic attack—the glucosinolates are able to be hydrolysed by endogenous myrosinase enzymes. Intact plant tissue separates glucosinolates from myrosinase enzymes by compartmentalising the former in S-cells and the latter in myrosin cells. Only upon cell rupture are the myrosinase enzymes able to hydrolyse the glucosinolates. Several types of compound are potentially formed, including isothiocyanates, thiocyanates, and nitriles 29).
Isothiocyanates are to date the most-studied and best-characterised of known glucosinolate-hydrolysis-derived products in terms of their bioactivity. They are believed to play a defensive role in the plants via their cytotoxic effects on microorganisms and small parasitic animals, but to be directly beneficial to human health via broad anti-inflammatory and antioxidant effects, and thus are able to help inhibit the development of cancers 30), cardiovascular diseases 31), and osteoarthritis 32). Broccoli is particularly high in a particular glucosinolate called glucoraphanin, whose myrosinase-mediated hydrolysis generates an isothiocyanate called sulforaphane (1-isothiocyanato-4-(methylsulfinyl)butane), the structure of which is depicted in Figure 1.
A multitude of experiments in test tubes and in laboratory animals reportedly demonstrate the ability of sulforaphane to both defend healthy cells against chemical and/or radiation-induced carcinogenesis 33), 34), 35) and to inhibit the proliferation, migration, invasive potential and survival of tumour cells 36), 37), 38).
There are other glucosinolates and metabolites found in cruciferous vegetables which possess similar chemistry, metabolism, and anticancer effects as sulforaphane (eg. glucobrassicin- I3C, gluconasturtiin- phenethylisothiocyanate, glucoerucin-erucin (sulfide analog of sulforaphane), glucoiberin-iberin) 39). Also, there is a large body of research that has examined sulforaphane effects on many other cancers such as breast, hepatic, bladder, osteosarcoma, glioblastoma, leukemia, pancreatic, and melanoma. Although larger scale clinical trials are necessary, dietary sulforaphane shows promise as a safe and effective anti-cancer strategy that includes incorporating easily accessible foods into an individual’s regular diet.
To date very few human clinical trials have evaluated the effects of sulforaphane on cancer outcome, however, several pilot and phase 1 human sulforaphane trials have been conducted utilizing different sources of sulforaphane. The first study was a randomized, placebo-controlled, double-blind phase 1 clinical trial of healthy volunteers that used glucoraphanin or isothiocyanate as the sulforaphane source 40). The phase 1 trial consisted of three study groups; 25 µmol of glucosinolate, 100 µmol of glucosinolate, or 25 µmol isothiocyanate for 7 days and examined parameters of safety, tolerance, and pharmacokinetics. Importantly, there were no significant toxicities associated with taking the extracts at the doses employed. A second study was a randomized placebo-controlled chemoprevention trial performed in Qidong, People’s Republic of China which used a hot drinking water infused with 3-day old broccoli sprouts 41). Residents of Qidong are at high risk for development of hepatocellular carcinoma, in part due to consumption of aflatoxin-contaminated foods, and are exposed to high levels of the airborne toxin phenanthrene. There was an inverse association for the excretion of dithiocarbamates and urinary aflatoxin-DNA adducts and trans, anti-phenanthrene tetraol, a metabolite of the combustion product phenanthrene in the intervention arm. Thus, an inverse correlation between sulforaphane treatment and excretion of carcinogens was detected, suggesting induction of one or more phase 2 enzymes. Interestingly, in the Qidong trial, although there was consistency within an individual between doses, there was significant inter-individual variability in bioavailability of the dithiocarbamates. A third small preliminary human study interested in determining if the HDAC inhibition effects observed in cell culture and mice could be translated into humans was performed. After ingestion of 68g of broccoli sprouts, a significant decrease in histone deacetylase activity was evident in peripheral blood mononuclear cells with a concomitant increase in acetylated histones H3 and H4 42). The most recent pilot human study was performed in 8 healthy women who were undergoing elective reduction mammoplasty. Here the women were given an oral dose of broccoli sprout preparation containing 200 µmol sulforaphane 1 h prior to breast surgery. Mean epithelial-/stromal-enriched breast tissue dithiocarbamate concentration was 1.45±1.12 and 2.00±1.95 pmol/mg tissue for the right and left breast, respectively. NQO1 and HO-1 transcript levels were measured in both breasts of all subjects 43). These clinical trials provide the important link to human relevance for sulforaphane as a promising anticancer agent.
Although commercially available as a supplement, sulforaphane has yet to be FDA approved for the treatment of human disease, including cancer 44). However, the chemopreventive properties of sulforaphane, and its capacity to be selectively toxic to malignant cells and impart these effects through a number of mechanisms, provide rationale to completely elucidate and evaluate its potential as an anti-cancer compound alone, and in combination with clinically relevant therapeutic and management strategies.
Table 2. Active metabolites of broccoli and their roles in cancer control
Table 3. Summary of Human Clinical Trials on Sulforaphane in Progress or Recently Completed
|Sulforaphane preparation||Subject information||Phase||Current status||Information/Results||Reference|
|Broccoli sprout extract given 200 μmol orally once daily for 1 week||Male (<18 years) with recurrent prostate adenocarcinoma||Phase II||Active, not recruiting||To determine: (1) therapeutic benefit, (2) safety profile, (3) pharmacokinetics, (4) pharmacodinamics)||NCT01228084; clinicaltrials.gov|
|Four-week treatment with sulforaphane glucosinolate capsules (250 mg broccoli seed extract daily)||Healthy male (21 years and older)||Prostate cancer prevention||Recruiting||To identify distribution of sulforaphane and HDAC inhibition in subjects at risk for prostate cancer (DNA methylation status and proliferation markers in -biopsy)||NCT01265953; clinicaltrials.gov|
|14 day intervention of broccoli sprout extract consisting of a consistent dose of sulforaphane dissolved in mango juice||Woman (<18 years) with ductal carcinoma in situ (DCIS–breast)||Phase II||Recruiting||To determine the therapeutic benefit (measure proliferative rate) of sulforaphane and evaluate the ability of sulforaphane to modulate specific cytoprotective enzymes||NCT00982319; clinicaltrials.gov|
|Broccoli sprout extract administered orally at 50, 100, or 200 μmol sulforaphane daily||Subjects (<18 years) must have at least two atypical nevi before diagnosis of melanoma.||Phase 0||Recruiting||To determine (1) adverse effects (2) visual and cellular changes in atypical nevi, (3) biodistribution, and (4) effect of sulforaphane on STAT-1 and -3 expression||NCT01568996; clinicaltrials.gov|
|High sulforaphane broccoli sprout extract (100 μmol sulforaphane) every other day for 5 weeks||Man (40–75 years) with low or intermediate grade prostate cancer||Phase I and II||Enrolling by invitation||To identify biological effects of sulforaphane on normal prostate tissue, and determine whether the consumption of broccoli sprout extract will inhibit growth of prostate cancer||NCT00946309; clinicaltrials.gov|
|Sulforaphane-containing broccoli sprout extract (topical application; 280 nmol daily)||Woman (<18 years) with pathlogically confirmed invasive adenocarcinoma or ductal carcinoma in situ of the breast||Phase II||Not recruiting||To investigate the protective effects of topical sulforaphane on radiation-induced dermatitis||NCT00894712; clinicaltrials.gov|
|Broccoli sprout extract beverage:|
600 μmol glucoraphanin, 40 μmol sulforaphane dissolved in 100 ml pinapple and lime juice daily for 84 days
|Healthy subjects (21–65 years)||Phase II||Completed||To assess the effect of sulforaphane treatment on level of air toxin mercapturic acid in urine.|
Broccoli sprout extract: 1.700 (1.235–2.386)
Placebo: 1.065 (0.686–1.826)
NOTE: no statistical analysis provided
No serious adverse effects reported
|Consumption of two portions per week of standard broccoli, glucoraphanin-enriched broccoli, or a high glucoraphanin-enriched broccoli soup for 1 year||Man (18–80 years) with low or intermediate prostate cancer||—||Enrolling by invitation||To assess the ability of sulforaphane to alter metabolism and gene expression within prostate tissue, and reduce the progression to aggressive cancer||NCT01950143; clinicaltrials.gov|
|Glucoraphanin-rich broccoli sprout extract (800 mmol) or sulforaphane-rich broccoli sprout extract (150 mmol) daily for 7 days dissolved in 100 ml mango juice||Healthy subjects (25–65 years)||Phase I||Completed||Statistically significant increase of 20%–50% in the levels of excretion of glutathione-derived conjugates of carcinogens, including acrolein, crotonaldehyde, and benzene in individuals compared with preintervention baseline values||NCT01008826; clinicaltrials.gov|
|Broccoli sprout grain capsule (90 mg sulforaphane) per day over 1 year||Subjects (<18 years) with advanced, surgically nontreatable pancreatic ductal adenocarcinoma||—||Not yet open for recruitment||To determine disease status and compound bioavailability||NCT01879878; clinicaltrials.gov|
|Broccoli sprout extract oral supplementation thrice daily for 2–8 weeks||Woman (<21 years) who has undergone a diagnostic mammogram||Phase II||Active||To determine (1) bioavailability, (2) effect of supplement on biomarkers of prognosis, and (3) effect on HDAC inhibition||NCT00843167; clinicaltrials.gov|
|Stabilized synthetic sulforaphane compound||Healthy man (18–45 years)||Phase I||Completed||To assess safety, tolerance, pharmacokinetics, and pharmacodynamics (NOTE: no data, has progressed further in human trials)||NCT01948362; clinicaltrials.gov|
|Raw or cooked broccoli (200 g)||Healthy subjects (22–50 years)||Phase 0||Completed||To determine bioavailability after consumption through analysis of urinary biomarkers, and to assess the affect of preparation on metabolic fate (NOTE: no data, however extensive research has been published)||NCT01743924; clinicaltrials.gov|
Abbreviation: BSE = broccoli sprout extract.
While all cruciferous vegetables (broccoli, cauliflower, cabbage, kale, bok choy, arugula, Brussels sprouts, collards, watercress and radishes) seem to be effective in fighting cancer, broccoli and broccoli sprouts are the most powerful 46). Even more promising results have been found in broccoli sprouts as those sprouts contain fifty times more anticancer agents than in fully mature broccoli 47). According to a study in Britain 48), combining broccoli with spicy foods that contain myrosinase (an enzyme) can actually enhance the cancer fighting properties of broccoli. The particular compounds in broccoli that are so effective against cancer include the phytochemicals or active metabolites, such as sulforaphane, erucin and the indole-3-carbinol (see Table 2).
Sulforaphane is a remarkably potent compound that fights cancer on various fronts specially melanoma 49), lung cancer 50), breast cancer 51), ovarian cancer 52) and colorectal cancer 53).
Sulforaphane inhibits histone deacetylase (HDAC) enzymes that are known to work against the ability of genes that suppress development of tumors 54). It has the ability to activate genes that can prevent cancer development 55). Sulforaphane also normalizes DNA methylation (the process of when a methyl group is added to a DNA molecule), which is a crucial part of normal cell function and suppressing bad genes in the early stages of prostate cancer 56) and colorectal cancer 57). At the cellular level, sulforaphane also helps the body to limit oxidation, the process that initiates many chronic diseases.
A case control study in China found that intake of broccoli, measured by urinary secretion of isothiocyanates, was inversely related to the risk of breast cancer 58). Also, prostate cancer risk was found to be reduced by cruciferous vegetable consumption in a population-based case control study carried out in western Washington State 59). Three or more servings per week, compared to less than one serving of broccoli per week resulted in a statistically significant 41 per cent decrease in prostate cancer risk 60). Another case study in Shanghai, China found that men with detectable amounts of isothiocyanates in their urine had a 35 per cent decreased risk of lung cancer 61). Previously in another study, it was found that bladder cancer was only weakly associated with low intake of fruits and vegetables, but high intake (5 or more servings a week versus 1 or less serving a week) of broccoli was associated with a statistically significant 51 per cent decrease in bladder cancer 62).
Just like sulforaphane, erucin is a natural isothiocyanate. Erucin has both anticancer and chemopreventive activities which is effective against breast cancer 63), pancreatic tumorous growth 64) and hepatocellular carcinoma 65). However, erucin is present in trace amount in broccoli. It is abundant in rocket (Eruca vesicaria) and in some other cruciferous vegetables.
On the other hand, indole-3-carbinol is a natural compound derived from the breakdown of the glucosinolate glucobrassicin. This active metabolite has shown antiproliferative effects in several colon cancer cell lines and reactivation of phosphatase and tensin homologue (PTEN) proteins in prostate cells. A lower risk of colorectal cancer 66) and prostate cancer 67) was found to be associated with a high intake of broccoli. It is thought to
be an effective breast cancer preventing phytochemical which blocks estrogen receptors in breast cancer cells. Recently, it has been found the consumption of cruciferous vegetables is associated with a low breast cancer risk in Chinese women 68).
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