The Cancer Research
Despite nutrition advice to “eat the rainbow,” cauliflower provides an example of why you shouldn’t overlook white-colored foods. It’s a nutrient-rich cruciferous vegetable that pairs well with many foods and flavors.
Cruciferous vegetables have been relatively well-studied regarding cancer prevention. In lab studies, their compounds show good protective potential. So far, high quality human studies give a mixed picture about lower cancer risk. It’s possible that benefits vary based on individual differences and how these vegetables are prepared.
Interpreting the data
After a systematic review of the global scientific literature, AICR/WCRF analyzed how vegetables and their nutrients affect the risk of developing cancer.
“Convincing” or “probable” evidence means there is strong research showing a causal relationship to cancer—either decreasing or increasing the risk. The research must include quality human studies that meet specific criteria and biological explanations for the findings.
A convincing or probable judgement is strong enough to justify recommendations.
- There is probable evidence that non-starchy vegetables and fruit combined DECREASE the risk of:
- Aerodigestive cancers overall (such as mouth, pharynx and larynx; esophageal; lung; stomach and colorectal cancers)
“Limited suggestive” evidence means results are generally consistent in overall conclusions, but it’s rarely strong enough to justify recommendations to reduce risk of cancer.
- Limited evidence suggests that foods containing vitamin C may DECREASE the risk of:
- Lung cancer (in people who smoke) and colon cancer
- Limited evidence suggests that non-starchy vegetables may DECREASE the risk of:
- Estrogen receptor-negative (ER-) breast cancer
- Limited evidence suggests that non-starchy vegetables and fruits combined may DECREASE the risk of:
- Bladder cancer
Ongoing Areas of Investigation
- Laboratory Research
Vitamin C is a powerful antioxidant. In lab studies, it protects cells’ DNA by trapping free radicals, and it helps renew the antioxidant ability of Vitamin E. In cell studies, vitamin C also inhibits formation of carcinogens and supports the immune system.
Glucosinolates in vegetables are broken down into isothiocyanates (such as sulforaphane) and indoles. In laboratory studies, these compounds decrease inflammation that could cause cell damage leading to cancer. They also inhibit enzymes that activate carcinogens and stimulate enzymes that de-activate carcinogens. These compounds turn on tumor suppressor genes, slow abnormal cell growth and stimulate self-destruction of abnormal cells.
- Indole compounds decrease development of breast cancer in cell and animal studies. In some studies, indoles shift the active form of estrogen into a weaker form. (High amounts of estrogen are a risk factor for certain hormone-linked cancers).
Folate helps maintain healthy DNA and keeps cancer-promoting genes “turned off”. Animal studies, however, suggest that providing this vitamin in exceptionally high amounts or after cancer cells have already formed might promote development of cancer.
- Human Studies
Human studies related to cauliflower and cancer risk compare groups of people who consume relatively high and low amounts of total vegetables, cruciferous vegetables and/or levels of vitamin C.
People who eat more vegetables and fruits have lower risk of a wide range of cancers. This probably reflects combined protection from many different nutrients and compounds they contain. Analysis from two large cohorts combined that was published after the AICR/WCRF Third Expert Report shows a lower risk of breast cancer in women consuming more than 5.5 servings/day total vegetable and fruit intake compared to women consuming 2.5 or fewer servings.
Vitamin C: Population studies comparing people with higher and lower levels of vitamin C in their diets, and especially levels circulating in their blood, link higher amounts with lower overall risk of cancer. This effect is larger comparing people with very low levels to moderately increased levels than comparing people with moderate and much higher levels. Higher levels of vitamin C from foods are linked with lower risk of lung cancer among people who smoke tobacco, although not in those who used to smoke or who have never smoked. People with more vitamin C in their diet are also less likely to develop colon cancer. That’s even after adjusting for other risk factors for colon cancer, such as alcohol, red meat and tobacco. Evidence for both lung and colon cancer is rated as Limited Suggestive in the AICR/WCRF Third Expert Report, and more research is needed.
Cruciferous vegetables: An analysis that combined several population studies showed an association of cruciferous vegetables with reduced overall cancer risk, although there are inconsistencies between studies. Part of the inconsistent findings may stem from genetic differences that allow isothiocyanate compounds to remain in the body longer in some people than in others. Differences in microbes that make up the gut microbiota can also lead to differences in compounds people absorb. Human studies are also complicated to interpret because people who eat the same amount of cruciferous vegetables may get different amounts of the protective nutrients and compounds depending on how the vegetables are prepared.
- Prostate cancer: An analysis of 13 observational population studies reported higher cruciferous vegetable consumption associated with lower prostate cancer incidence. However, when looking only at studies less likely to be affected by bias (prospective cohort studies), no association was seen. In analysis for the AICR/WCRF Continuous Update Project, no significant association was seen for total prostate cancer or for advanced forms specifically.
- Breast cancer: Analysis from two large cohorts combined that was published after the AICR/WCRF Third Expert Report found cruciferous vegetables associated with lower risk of breast cancer. This is consistent with the lower risk of post-menopausal breast cancer (but not pre-menopausal cancer) with high cruciferous vegetables in an earlier analysis that included some prospective cohort studies. More research is needed to understand this possible association.
Folate: Research on folate and cancer is challenging to interpret, since effects may differ based on time in the cancer process, amount consumed and individual genetic differences. Levels of folate from food and in the blood that are too low are linked with greater risk of several forms of cancer in some population studies. However, excess folic acid from randomized controlled trials with supplements has increased risk of some cancers. (Folic acid is the form of folate in supplements and fortified foods.) More research is needed to understand the amounts that are high enough to pose risk.
Featured Studies
- Tips for Selection, Storage and Preparation
Selection:
- Choose compact, firm heads. Green leaves should be fresh with no yellowing.
- Traditional white cauliflower should have a creamy white head without brown spots.
- Cauliflower also comes in orange, purple or green (which is sometimes called broccoflower) varietals that have been developed through natural selective plant breeding. The purple variety is a source of anthocyanin phytocompounds (a type of flavonoid polyphenol). It has a milder, slightly nuttier, flavor than traditional white cauliflower.
Storage:
- Wait to wash until just before use.
- Refrigerate in an unsealed plastic bag; cauliflower keeps for up to 5 days.
- After cooking, it keeps up to 3 days with good flavor.
Preparation Ideas:
- Steam, microwave, stir-fry or sauté to retain glucosinolates, folate and vitamin C. Boiling in a pot of water can cut content of these substances in half.
- Cauliflower’s flavor is very sensitive to how you cook it. Overcooking makes it watery, smelly and unattractive. So cook just until crisp-tender (for example, about 4-10 minutes when steaming). An extra benefit of limiting cooking time is that it’s the key to getting more of the protective compounds that form from glucosinolates.
- You can also roast or bake cauliflower, either cut into florets or as cauliflower “steaks” created by chopping the whole head of cauliflower into slices ½- to ¾-inch thick.
- Add to soup, pasta sauces and salads. When steamed until soft, cauliflower can be pureed and served as a side dish, mixed with mashed potatoes or stirred into soup.
- Dip raw cauliflower in hummus or yogurt-based herb dips. If the flavor is too strong to enjoy raw, steam or blanch briefly and cool quickly in ice water before serving.
- Frozen cauliflower can become soft when cooked, so you may enjoy it in soups and purees.
- Cauliflower has a slightly peppery taste, so it pairs well with flavorful sauces. It’s a popular part of Indian dishes, where it combines with curry and garlic flavors, and flavorful Italian dishes.
References
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