Fish fights obesity
diet of fish and low plasma levels of leptin, the hormone thought
to regulate appetite.
Evidence from Africa suggests that eating fish every day can help fight off the risk of obesity, report scientists from the Mayo Clinic in the US.
Writing in the journal Circulation, Dr Virend K. Somers and his colleagues explained that their study of one African tribe had revealed a correlation between a daily diet of fish and low plasma levels of leptin, the hormone thought to regulate appetite.
Although the exact function of leptin is unknown, it is thought to act as a messenger between the brain and the body, telling the former to reduce the appetite when the fat cells have reached capacity. If this system malfunctions, the brain does not tell the body that it is full, and so we continue to eat - hence the hormone's link with obesity and heart disease.
Somers said that his research was based on earlier evidence that fish could counteract the effects of increased leptin levels. His team looked at more than 500 individuals belonging to two tribes in Tanzania. One of the tribes had a high fish diet, eating it on a daily basis, while the other ate fish only rarely.
Both tribes consumed roughly the same number of calories each day, and both had similar lifestyles, but the tribe which lived close to a lake took almost a quarter of these calories from fish, compared to fruit and vegetables for the other tribe which lived more inland.
The team discovered that the male members of the fish-eating tribe had around 2.5 nanograms of leptin per millilitre of blood, less than a quarter of the level recorded among male members of the other tribe. In the same way, female fish-eaters were found to have just 5ng/ml of leptin compared to 12ng/ml for the fruit-eaters.
"These findings may have implications for understanding the reduced cardiovascular risk in subjects on a high-fish diet," Somers said. He added that the findings were not affected by obesity, as both tribes had virtually identical body mass indices, and that the relationship between fish and leptin levels remained the same regardless of age, alcohol consumption or insulin.
"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," Somers said, although he stressed that it was unclear whether this phenomenon was unique to the Tanzanian tribes or if it could be replicated elsewhere.
"We don't know if the findings will apply to a semi-overweight, urban-dwelling North American population," he said.
