Omega-3 Fats from Fish Oil Raise Risk of High-Grade Prostate Cancer

It has been increasingly evident that there are trade-offs in the quest to get and stay healthy. In other words, there are actions we can take that will reduce the risk of one health problem, but increase the risk of another. One example is playing high-impact sports such as basketball, which is great for improving and maintaining physical fitness while having fun, but also increases the risk of sprains, strains and other musculoskeletal problems. Now, an article by Brasky et al. in the American Journal of epidemiology (published online April 24, 2011)  points up a trade-off involved in taking fish-oil supplements, which have been widely recommended for reducing the risk of cardiovascular diseases and other health problems.

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

Results
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.

Bottom Line
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.

Our Changing Eating Patterns

The U.S. Department of Agriculture recently published information on the sources of our daily caloric intake between 1970 and 2008, a time period in which our daily caloric consumption increased by 23.2% from 2,169 cals to 2,672 cals, and rates of overweight and obesity have risen sharply. An interactive graphic was created from the data that allows users to scroll along a time-line to see how the amount of daily calories in each food category has changed over time. The following are the percentage changes in calories coming from each food category:

meat, eggs, and nuts: +4.1%
fruit:                         +22.9%
added fat:                 +56.3%
dairy:                          -3.7%
grains:                      +44.7%
vegetables                   -2.4%
added sugar              +14.2%

Some Observations on the Data

In Terms of Absolute Calories

• The biggest contributors by far to our increased daily caloric intake are added fat (231 cals) and grains (193 cals).
• Much more modest contributors to our increased daily caloric intake are added sugar (57 cals), meat/eggs/nuts (19 cals), and fruit (16 calories).
• Our daily consumption of dairy actually decreased by 10 calories and of vegetables by 3 calories.

In Terms of Percentage of Daily Calories

• The only foods that increased as percentages of our diet from 1970 to 2008 are added fats (from 18.9% to 24.0% of daily calories) and grains (from 19.9 % to 23.4% of daily calories).
• Caloric consumption from fruit was steady at 3.2 % of calories.
• All other foods declined as percentages of our daily calories including meat/nuts/eggs (from 21.3% to 18.0% of daily calories), dairy (from 12.3% to 9.6% of daily calories), added sugar (from 18.5% to 17.2% of daily calories), and vegetables (from 5.8% to 4.6% of daily calories).

Bottom Line
The greatest contributors to our increase in caloric consumption are grains and added fat. While we have increased our intake of all other foods except vegetables, grains and fat together account for 84% of our increase in caloric consumption and should therefore be the prime focus of cutting back calories. This makes it clear that the low-fat and low-carb diets are both missing something because the intake of both must be reduced. Any diet that emphasizes what you eat rather than how much you eat is bound to fail. Overweight and obese people who seek to attain a healthy body weight must face the reality that total intake must be lessened. Focusing on eating both fewer grain-based foods and fewer added fats is a good start.

Eating Nuts Provides Several Health Benefits

An article in the January 2011 Harvard Health Letter listed several health benefits of eating nuts. Although the calories in nuts come mainly from fat, the type of fat is largely of the unsaturated healthful variety. The article cited a study done at the Beth Israel Deaconess Medical Center showing that walnuts eaten at breakfast made subjects feel more full before lunch, potentially reducing caloric consumption. Other health benefits include favorable effects on blood cholesterol, blood pressure, and inflammatory factors. Studies on large populations have linked high nut consumption with lower heart disease rates. Nuts also contain little or no carbohydrate so they do not cause spikes in blood sugar and may even blunt blood sugar spikes caused by carbohydrates eaten along with the nuts. Peanuts, almonds, and pistacios have the highest protein content, while brazil nuts, cashews, hazelnuts, and walnuts have intermediate protein content, and pecans and macadamias have the lowest protein content. Walnuts have the additional benefit of being high in omega-3 fatty acids, which are widely considered the most healthful kind.