How can we measure the benefits of a diet that reduces the glycemic index and intake of omega-6s?

To continue our discussion following my recent post on green tea, I’d like to introduce the subject of the benefits provided by a diet low in glucides and omega-6s.

REMINDER Note that taking post-menopausal hormone replacement therapy for more than five years increases the risk of developing breast cancer by between 15 and 40% (in other words, by a factor of 1.15 – 1.4). Smoking, in comparison, increases the risk of developing lung cancer 15 to 35 years later by a factor of 15.

GLYCEMIC INDEX Several studies suggest that people who have a low glycemic-index diet are better protected against certain cancers. A Harvard study (Michau et al. 2005) observed a reduction of between 30 and 40 percent in colon or rectal cancer. In another study, the same research group found a reduction of 70 percent in the risk of developing ovarian cancer (Augustin et al., 2003). Overweight women who had a diet with a high glycemic index had 160% more risk of pancreatic cancer than those with a low glycemic-index diet (Michaud et al., 2002).

OMEGA-6 and OMEGA-3 fats Regarding omega-6 and omega-3 oils, a Singapore study gives us an idea of their potential benefit. Analysis of more than 35,000 women showed that those who consumed higher quantities of omega-6s (and no omega-3s) increased their risk of developing “advanced” breast cancer by a factor of 2.45 (145% increase). Those who consumed oily fish at least twice a week had no increase in risk, even if their diet also contained omega-6s (Gago-Dominguez, 2003). A Harvard study that analyzed 4,782 men over a period of several years also found that those who ate oily fish two or three times a week reduced their risk of developing advanced (metastastizing) prostate cancer by half compared to men who ate little or no oily fish (Augustsson et al. 2003). Three years later, another study, this time at the University of San Francisco, examined the progression of existing prostate cancer, and confirmed the benefit of eating fish at least twice a week. (However, in this study the benefit derived from fish was a little weaker, involving “only” 25 percent fewer advanced cancers - Chan et al. 2006)

In Europe, the massive, long-term EPIC study, analyzing the diet of almost 500,000 people, has shown an almost 70% reduction in risk (in other words a factor of two and a half!) of developing colon cancer in people who habitually ate 80 grams (2.8 oz) of fish daily. This is, it’s true, a lot of fish. (Norat et al. , 2005)

What seems to matter most is the balance between omega-6 et omega-3 fatty acids. If enough omega-3s are consumed, the omega-6s don’t seem able to induce the inflammatory conditions that favor development of several chronic, degenerative diseases, including cancer.

CONCLUSION What can we conclude from all this? Firstly, the nutritional factors that contribute to cancer don’t represent anything like the kind of danger that tobacco does. However, it’s clear that careful nutritional choices can deliver significant protection. According to these various studies, a careful diet can have much more impact than the decision to refrain from hormone replacement therapy. In addition, no studies to date have studied the impact of a diet that combines all the variables – green tea + low glycemic index + reduction of omega 6s and increase of omega 3s + turmeric + herbs + broccoli three times a week + garlic/onions/leeks + red berries, etc. None of the existing studies suggest that these foods interact negatively on each other in ways that might reduce their positive effect. We may on the contrary suppose that combinations of these foods will target a larger number of mechanisms that act on the growth of tumors, and thus lead to a very beneficial “synergy” effect.

BIBLIOGRAPHY Michaud DS, Liu S, Giovannucci E, Willett WC, Colditz GA, Fuchs CS. Dietary sugar, glycemic load, and pancreatic cancer risk in a prospective study. Journal of the National Cancer Institute 2002;94(17):1293-300. Michaud DS, Fuchs CS, Liu S, Willett WC, Colditz GA, Giovannucci E. Dietary glycemic load, carbohydrate, sugar, and colorectal cancer risk in men and women. Cancer Epidemiology, Biomarkers & Prevention 2005;14(1):138-47. Augustin LSA, Polesel J, Bosetti C, et al. Dietary glycemic index, glycemic load and ovarian cancer risk: a case-control study in Italy. Annals of Oncology 2003;14(1):78-84. Gago-Dominguez M, Yuan J, Sun C, Lee H, Yu M. Opposing effects of dietary n-3 and n-6 fatty acids on mammary carcinogenesis: The Singapore Chinese Health Study. British Journal of Cancer 2003;89(9):1686-92. Augustsson K, Michaud D, Rimm E, et al. A prospective study of intake of fish and marine fatty acids and prostate cancer. Cancer Epidemiology, Biomarkers & Prevention 2003;12(1):64-7. Chan JM, Holick CN, Leitzmann MF, et al. Diet after diagnosis and the risk of prostate cancer progression, recurrence, and death (United States). Cancer Causes & Control 2006;17(2):199-208. Norat T, Bingham S, Ferrari P, et al. Meat, fish, and colorectal cancer risk: the European Prospective Investigation into cancer and nutrition. Journal of the National Cancer Institute 2005;97(12):906-16.