Prostate cancer is the second most common cancer in American men. Estimates are that in 2013, nearly 240,000 new cases of prostate cancer will be diagnosed and nearly 30,000 men will die from this disease. Although about one man in six will be diagnosed with prostate cancer during his lifetime, this disease occurs mainly in older men and most men with prostate cancer do not die from their disease. Delaying the onset and/or slowing the growth of prostate cancer even modestly can profoundly reduce prostate cancer mortality as men will die with their cancer rather than of their cancer. There is evidence that diet can play a role in this regard.
Dietary habits that reduce inflammation may help reduce risk of prostate cancer. Inflammation is thought to play a role in the etiology of many cancers. In general, the long chain omega-3 fatty acids that are found in certain types of fish are believed to be anti-inflammatory and therefore, potentially protective against prostate cancer. However, recent research published in the Journal of the National Cancer Institute suggests otherwise.
The investigators, who were affiliated with universities throughout the United States, measured blood levels of different fatty acids in 834 men diagnosed with prostate cancer, of which 156 had advanced cancer. They compared the levels with those of 1393 men without cancer of similar age and race. Blood levels were used as a surrogate for dietary intake. For the analysis, men were divided into four groups according to their fatty acid levels. Surprisingly, in comparison to the group of men with the lowest blood levels of long-chain omega-3 fatty acids, men with the highest levels were nearly 50% more likely to have prostate cancer and 70% more likely to have advanced prostate cancer. In other words, consuming more of the omega-3s from fish increased risk.
In contrast, risk of prostate cancer was unrelated to blood levels of alpha-linolenic acid, the type of omega-3 fatty acid found in plant foods such as soybeans and flaxseed, which is an essential fatty acid. Furthermore, linoleic acid, an essential omega-6 polyunsaturated fatty acid, was protective against prostate cancer. Linoleic acid is abundant in soybeans and oils such as corn oil and soybean oil. Men in the highest category of blood linoleic acid levels were 25% less likely to have prostate cancer.
The results of this study suggest that men are well advised to consume soyfoods and soybean oil. These products provide both essential fatty acids without providing the long-chain omega-3 fatty acids associated with an increased risk of prostate cancer.