New research finds that members of an African tribe who eat fish every day have relatively low blood levels of leptin, the "obesity hormone" thought to be involved in appetite regulation. Fat cells and other tissues in the body produce leptin, which is believed to notify the brain to reduce appetite when fat cells are "full." Exactly how the hormone works to control appetite is uncertain, however.
Leptin is believed to be involved in fat metabolism and weight gain. Previous research has linked high levels of leptin to an increased risk of heart disease, while eating fish has been shown to reduce that risk.
The researchers feel that a diet rich in fish is associated with lower plasma leptin, independent of body fat. The team measured the effect of fish consumption on leptin levels in the blood by comparing two neighboring tribes in Tanzania, one whose 279 members consumed fish daily, while the 329 members of the other tribe ate fish only rarely.
Both tribes consumed around the same number of calories each day, and both maintained similar lifestyles. However, the group that lived close to a lake consumed about 25% of their total calories from fish, while the other, whose members lived further inland, consumed most of their calories from fruits and vegetables.
The study revealed that male fish-eaters had lower levels of leptin than the male vegetarians. Female fish-eaters also had markedly lower leptin levels than their vegetarian peers. Members of both tribes had virtually identical body mass indices, an indication of obesity that measures weight in relation to height. This suggests that these findings are not influenced by obesity.
The scientists 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. However, they don't know if the findings will apply to a semi-overweight, urban-dwelling North American population.
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