A recent analysis of European Population Data (the EPIC study) conducted at the Mount Sinai Tisch Cancer Institute and published on-line in the Journal of the National Cancer Institute concluded that eating more fruits and vegetables has “a protective effect against cancer”, but that “any cancer protective effect of these foods is likely to be modest, at best.” (Bofetta et al., 2010) Dr. Boffetta and colleagues found a small but significant inverse relationship between high intake of fruits and vegetables and overall cancer risk. In this population, an increase of 200 grams a day of fruits and vegetables resulted in a reduction of about 3 percent of cancer risk.

I think it is essential to put such results in perspective to really understand what they may, or may not, mean about the importance of diet in terms of preventing, or slowing down, cancer.

First, just "more fruits and vegetables" in isolation doesn't say much can't be expected to beat cancer. You wouldn't even expect a single chemotherapy agent to do much when it comes to cancer, they're always combined, and often with surgery and radiotherapy too. Who says we need to prove that fruits and vegetables, on their own, can beat the disease?

Second, when it comes to an Anticancer diet, there is good evidence that adhering to a Mediterranean diet (which is more than just "five fruits and vegetables per day") reduces the risk of developing cancer by roughly 50% (Knoops et al. 2004). This supports the argument in favor of combination effects from several Anticancer nutrients and strategies (including omega-3 fatty acids, terpenes from aromatic herbs, legumes and whole grain cereals, decreased amounts of refined sugar, etc.). Indeed, no single nutrient or food or even food group is likely to make a significant difference. But a whole diet will.

Third, there is evidence from a UCLA study (Pierce et al. 2007), that after full treatment for breast cancer, women whocombination of Anticancer life style changes just add more fruits and vegetables to their diet don't improve their survival curves much beyond women who don't change anything to their lifestyle. Women who start a regular physical activity 30 minutes 5 days a week improve their survival modestly over the first 6 years or so, but after a few more years their survival curve is no different from the women who didn't change anything. YET, women who do BOTH (add more fruits and vegetables AND more physical activity) experience a significant improvement in survival over the 9 years of follow-up post treatment. Obviously, as for chemotherapy, it is important to COMBINE anticancer life-style changes in order to get significant benefits.

From Pierce et al. 2007, Journal of Clinical Oncology:
Fourth, considering "fruits and vegetables" as a general category, is a bit like talking about "medication" as a general category. Bananas and potatoes for example may raise blood sugar and contribute to inflammation rather than help slow down cancer. So studies that don't specify WHAT fruits and vegetables (and they generally don't) can't add much to the debate. It would be more meaningful to measure the amount of cruciferous vegetables, of onions/garlic/leeks, of mushrooms, of berries, of stone fruits, etc. -- i.e., vegetables and fruits that have a documented anticancer activity.

MY ADVICE: don’t let the partial and over-interpreted results of this recent publication in the very conservative Journal of the National Cancer Institute discourage you from pursuing an active Anticancer – and health promoting – lifestyle!

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References:

Boffetta, P., et al., Fruit and Vegetable Intake and Overall Cancer Risk in the European Prospective Investigation Into Cancer and Nutrition (EPIC). J. Natl. Cancer Inst., 2010: p. djq072.

Knoops, K.T.B., et al., Mediterranean Diet, Lifestyle Factors, and 10-Year Mortality in Elderly European Men and Women - The HALE Project. JAMA, 2004. 292: p. 1433-1439.

Pierce, J.P., et al., Greater Survival After Breast Cancer in Physically Active Women With High Vegetable-Fruit Intake Regardless of Obesity. Journal of Clinical Oncology, 2007. 25(17): p. 2345-2351. Bibliography