Nutrition

Epidemiological studies on cruciferous vegetables & cancer risk

(from the American Association for Cancer Research)

"94 studies from the Netherlands Organization for Applied Scientific Research, Nutrition and Food Research Institute showed that with an increase in the consumption of cabbage, cauliflower, broccoli etc., the risk of many types of cancer decreased.

On the cancer-preventive effect of cruciferous vegetables, including cabbage, kale, broccoli, Brussels sprouts, and cauliflower:

The protective effect of brassicas against cancer may be due to their relatively high content of glucosinolates. Certain hydrolysis products of glucosinolates have shown anticarcinogenic properties.

7 cohort studies and 87 case-control studies on the association between brassica consumption and cancer risk were analyzed. The cohort studies showed inverse associations between the consumption of cabbage, cauliflower, and broccoli and risk of lung cancer; between the consumption of brassicas and risk of stomach cancer; between broccoli consumption and risk of all cancers taken together; and between brassica consumption and the occurrence of second primary cancers.

Of the case-control studies, 67% showed an inverse association between consumption of total brassica vegetables and risk of cancer at various sites. For cabbage, broccoli, cauliflower, and Brussels sprouts, these percentages were 70, 56, 67, and 29%, respectively.

Although the measured effects might have been distorted by various types of bias, it is concluded that a high consumption of brassica vegetables is associated with a decreased risk of cancer.

This association appears to be most consistent for lung, stomach, colon, and rectal cancer and least consistent for prostatic, endometrial, and ovarian cancer. It is not yet possible to resolve whether associations are to be attributed to brassica vegetables per se or to vegetables in general. Further epidemiological research should separate the anticarcinogenic effect of brassica vegetables from the effect of vegetables in general."

In 1997, Fahey, Zhang, and Talalay (researchers at Johns Hopkins University) published a study (Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens) showing that 3-day-old sprouts of broccoli, cauliflower and some other crucifers contained up to 100 times higher levels of cancer-fighting sulforaphane compounds than the corresponding mature plants, following up from an earlier (1994) study demonstrating anticarcinogenic activities of sulforaphane.

Compare Broccoli (sprouts or extract) may halt growth of breast cancer cells.

Preserving nutrient value of fresh broccoli in preparation

According to Cristina Garcia-Viguera writing in the Journal of the Science of Food and Agriculture, a study that analyzed antioxidant levels in broccoli subjected to various types of kitchen preparation yielded the following results:

Steamed broccoli retained about 89 percent of its original antioxidant content. Pressure cooking allowed broccoli to preserve c. 46 percent (in fact c. 91 percent if the cooking water was consumed as well).

Boiling retained only about 20 percent of antioxidants in the dish (and c. 35 percent with inclusion of the cooking water). And microwaving nearly “killed” all antioxidants originally present in the broccoli (less than 5 percent of them survived), another example showing that microwaving doesn’t seem advisable for health-conscious consumers.

From a 2007 news item published at
biologynews.net/archives/2007/05/16/research_says_boiling_broccoli_ruins_its_anticancer_properties.html:
"Researchers at the University of Warwick have found that the standard British cooking habit of boiling vegetables severely damages the anticancer properties of many Brassica vegetables such as broccoli, Brussel sprouts, cauliflower and green cabbage.

"...Past studies have shown that consumption of Brassica vegetables decreases the risk of cancer. This is because of the high concentration in Brassicas of substances known as glucosinolates which are metabolized to cancer-preventive substances known as isothiocyanates.

"Boiling appeared to have a serious impact on the retention of those important glucosinolate within the vegetables. The loss of total glucosinolate content after boiling for 30 minutes was: broccoli 77%, Brussel sprouts 58%, cauliflower 75% and green cabbage 65%.

"The effects of other cooking methods were investigated: steaming for 0-20 min, microwave cooking for 0-3 min and stir-fry cooking for 0-5 min. All three methods gave no significant loss of total glucosinolate analyte contents over these cooking periods."

If you chew thoroughly, you might want to eat your broccoli raw or sprouted (as above suggested) for maximum nutrition (cooking and other processes, in addition to the above-listed disadvantages, also destroy enzymes).

“Brassica family prevents precancerous cells turning into potentially deadly cancer cells”

Summary: Further evidence that eating vegetables protects against cancer was unveiled by Professor Ian Johnson, of the Institute of Food Research. He said millions of people put themselves at increased risk of cancer because they do not appreciate the benefits of eating fruit and vegetables. His research shows that certain chemicals in brassicas kill colon cancer cells in the same way as anti-cancer drugs. Lab tests showed that a chemical called allyl-isothiocyanate (AITC), which is released when the food is chopped, cooked or chewed and gives these vegetables their bitter flavour, stops the uncontrolled division of cancer cells that allows tumours to grow. (Daily Mail; The Sun; Daily Telegraph) [www.organicfood.co.uk]

Scientists think they are unravelling the secret of just why greens are good for you in the fight against cancer.

Chemicals in some brassica vegetables, such as cabbage, cauliflower, broccoli and brussels sprouts, sabotage colon cancer cells in a similar way to that employed by some cancer drugs.

Two to three portions a week of such foods might offer protection against colon cancer, [Professor] Ian Johnson, leader of a research team at Institute of Food Research told a press conference in London yesterday.

Eating five portions of fruit and vegetables a day is one of the key government health messages because of the protective anti-cancer effects but the evidence for this is largely based on studying cancer rates between different populations with different diets. Low consumption of fruit and veg is thought to double an individual's risk of developing colon cancer, which kills around 16,200 patients annually.

But now researchers at the Norwich-based institute believe they are beginning to understand the mechanism by which the brassica family prevents precancerous cells turning into potentially deadly cancer cells.

Brassica is also thought to offer protection against lung and prostate cancers. It is known that the breakdown of sinigrin, a compound found in brassica, seems to kill cancer cells. But the active agent from that breakdown appears to be a chemical (allyl-isothiocyanate, or AITC) created when the vegetables are chopped, chewed and digested. AITC seems to prevent cancer cells becoming "immortal", the property that makes them different from healthy cells which "commit suicide" instead of dividing infinitely.

Compare Broccoli (sprouts or extract) may halt growth of breast cancer cells.

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