Not just any fish for omega-3 fatty acids

Previous studies on the relationship between fish consumption and the blood levels of omega-3 fatty acids have been focused mainly on those populations who eat fish frequently. Further, the fish these groups eat tended to be saltwater fish almost exclusively. Canadian researchers recently designed a study to cover those research gaps: their study focuses on those who only eat moderate amounts of fish and tend to eat more freshwater fish than saltwater fish (Am J Clin Nutr 2006; 84:1299-1307).

They recruited by advertising for volunteers through the regional environmental and fishers associations. Those eligible were over 18 and reported eating fish from local lakes. The resulting group contained 243 persons between the ages of 18 and 74, of which 53% were men.

Each volunteer filled out a questionnaire which included questions about age, sex, income, education level, lifestyle habits (such as smoking and drinking alcohol), known illnesses, and medications. Another questionnaire asked about their fish diet throughout the year, detailing specific fish species, where the fish came from (freshwater catch, the market, canned or other), the amount consumed and how often fish was eaten per week. Their Body Mass Index was measured by a nurse and their blood was drawn to measure their blood levels of omega-3 and omega-6 fatty acids.

Freshwater fish made up 73% of the total intake of those who ate the most fish in this study. Of that freshwater fish, 89% was lean fish, or those species which contain less than 0.5 gram of fatty acid per 100 grams of fish. By contrast, a freshwater fatty fish such as trout contains over three times the amount of fatty acids.

After correlating the amount of fish consumed with the subjects' blood levels of fatty acids, the researchers were surprised to find that those who ate the most fish had a blood level of fatty acids similar to those who only ate fish occasionally. Again, lean fish made up 88% of the total fish intake for these fish consumers. The scientists theorize that the types of fish may have an impact on how well the body incorporates the fatty acids into the bloodstream.

What this means for you

Lean freshwater fish such as trout, bass, and whitefish may not be the best source of omega-3 and omega-6 fatty acids, but they're still delicious and low in both calories and fat. Try a trout recipe: Baked Cumin Trout with Squash and Pumpkin Seeds or Pumpkin-Crusted Trout.

First posted: January 9, 2007