The researchers analyzed blood samples of 3,461 men to measure levels of omega-3 fats (DHA and EPA from fish consumption), omega-6 fats (from common vegetable oils), and trans-fats (from hydrogenated oils in margarine, shortening, and processed foods). The men were then followed over a 7-year period in order to see the association of the different fat types to the incidence of prostate cancer. The hypotheses were that:
- Because of the anti-inflammatory effect of the omega-3 fats, men with the highest blood levels of them would have a lower incidence of prostate cancer
- Because of the inflammatory effect of the trans- fats, men with the highest blood levels of them would have a higher incidence of prostate cancer
The statistical analysis produced the following surprising results:
> There were no effects of any of the fat types on overall incidence of prostate cancer.
> When looking at the high-grade form of prostate cancer that progresses rapidly and is the most lethal:
- Those men with the highest blood levels of DHA from fish oil had more than twice the risk of contracting high-grade prostate cancer as men with the lowest blood levels of DHA.
- EPA from fish oil had no effect on the incidence of high-grade prostate cancer.
- Those men with the highest blood levels of trans-fats had about half the risk of contracting high-grade prostate cancer as men with the lowest blood levels of trans-fats
- Blood levels of the type of omega-3 fat from vegetable sources (e.g. flax seeds, walnuts) had no effect on the incidence of high-grade prostate cancer.
The results of highly surprising, given the widespread view of fish oil as all-good and trans-fats as all-bad. Here is a clear case of trade-off. There is considerable evidence that fish-oil is good for the heart and cardiovascular system and reduces the incidence of heart attacks. Yet, here we see that it increases the risk of high-grade prostate cancer. Eating omega-3 fats from flax-seeds or other vegetable sources is not a solution because that type of omega-3 fat has not been proven to reduce the risk of cardiovascular disease. The good news is that most prostate cancer is of the low-grade variety. Given that heart disease remains the number one killer of both men and women, it doesn’t appear that fish and fish-oil be abandoned as a health-promoting dietary elements. Yet men must be aware of the trade-off in risk of eating fatty fish or taking fish-oil supplements in order to make an informed decision about how best to promote their health.
Update (May 8, 2011):
Consumerlab.com, a company that tests the quality of supplements from various companies, contacted Dr. Theodore Brasky, the lead author of the study described herein. He stated that the blood levels of DHA and EPA measured in the study were largely based on fish consumption rather than fish-oil supplements. However, a recent study of his, soon to be published, shows no link between fish oil supplementation and risk of prostate cancer. He also noted another study (Szymanski, Am J Clin Nutr 2010) that found fish consumption associated with a large reduction in late state or fatal prostate cancer.