Fish-Rich Tribal Diet Linked With Low Leptin Levels

Leptin is secreted by fat tissue. In humans, leptin is a satiety factor, which in normal-weight people tells their bodies when they have consumed enough food. High leptin levels have been associated with obesity and increased risk for cardiovascular disease.

As people gain weight, the body may stop listening to the leptin message, so more leptin is produced, explains senior author Virend K. Somers, M.D., D. Phil., professor of medicine in the division of cardiovascular disease and hypertension at the Mayo Clinic, Rochester, Minn. However, among the African populations in this study, higher body fat was not clearly associated with increased leptin levels.

"Regardless of body fat or body mass index (BMI), leptin levels were substantially lower among the fish-eaters than among vegetarians," says Somers. "We speculate that a fish diet may change the relationship between leptin and body fat and somehow help make the body more sensitive to the leptin message."

BMI is a measure of body fat based on height and weight. Skin-fold thickness was also used to assess body fat. The average BMI among the people in the study, regardless of diet, was 20. A BMI value from 18.5 to 24.9 is considered healthy; BMI from 25.0 to 29.9 is overweight; and a BMI value of 30 or greater is obese.

Somers says leptin levels among the women were particularly noteworthy. Women usually have higher leptin levels than men, but in this study, women who ate the fish-rich diet had lower leptin levels than both men and women on the vegetarian diet.

The researchers compared leptin levels in two closely related African tribal populations living in Tanzania. The two groups are essentially the same tribe but they're separated geographically. One group lives close to a lake and the other lives inland. The inland-dwelling tribe primarily eats a diet high in fruits and vegetables, while the tribe living by the lake eats freshwater fish as a main component of their diet.

The researchers studied 279 people on the fish diet and 329 who ate the vegetarian diet. They compared average daily calorie intake and food consumption, BMI, body fat content, age and gender. Leptin, insulin and glucose levels were measured after an overnight fast.