ROCHESTER, Minn., July 1 (UPI) -- All things being equal -- including one's genes -- eating a diet rich in fish appears to be healthier for the heart than eating a vegetarian diet, researchers who studied members of an African tribe whose diet varies by village report.
The findings suggest a diet high in fish helps the body control blood levels of leptin, a substance secreted by fat tissue. High leptin levels have been associated with increased risk for heart attack and stroke.
Lead author of the study, Dr. Virend K. Somers of the Mayo Clinic in Rochester, said the results are particularly significant because the people studied have the same genetic makeup but simply eat different diets. Somers told United Press International leptin levels usually increase as people gain weight but in the new study people who ate fish continued to have low leptin levels even as they gained weight.
Heart researchers have been interested in leptin for several years because leptin in animals controls eating by sending a message to the brain when sufficient food is consumed. This "satiety" aspect of leptin also works in normal weight humans, but as people gain weight the leptin message is muted, Somers said. "So in obese people there are higher leptin levels because more leptin is needed to send the message when a person is 'full.'"
The new findings indicate fish somehow "changes the relationship between leptin and body fat and helps the body be more sensitive to the leptin message," Somers said. Not only did leptin levels not increase as weight increased among those eating the fish diets, but the fish had an even more marked effect on women, who normally have higher leptin levels than men. In this study "women's leptin levels were half that of men on the vegetarian diet," said Somers.
The average leptin level for men on the fish diet was 2.5 nanograms per milliliter. For women the average was 5.0 ng/mL. Men on the vegetarian diet registered an average leptin of 11.2 ng/mL and for women it was 11.8. Somers and colleagues studied 279 people who ate diets rich in fish and 329 who ate vegetarian diets.
Calling the findings "very interesting," Tufts University nutrition expert, Dr. Alice Lichtenstein also cautioned, "it is unclear how these findings relate to Westernized societies."
Somers agreed that the populations in his study are not typical of Americans. The subjects studied were members of a tribe living in Tanzania. Some of the tribe members live in a village close to a lake, while others live inland. The lake-dwelling tribe members eat a diet that includes 300 to 600 grams of fish a day and accounts for about a fourth of their total daily calories. The inland-dwelling tribe members eat a vegetarian diet. Both groups consume about 2100 calories a day.
One important factor is residents of both villages were fit and lean -- much more fit than "the average American," said study co-author Dr. Bradley Phillips of the University of Iowa in Ames. "And these people were eating about three fish meals a day, which would be pretty hard to sell to the American public."
Lichtenstein said consumers who are interested in heart-healthy diets should stick to current American Heart Association's recommendations to eat a diet "rich in fruits and vegetables, that includes two servings of fish a week."
The research is reported in the July 2 issue of the journal Circulation.
(Reported by Peggy Peck, UPI Science News, in Cleveland)