Clues as to How Fish Lowers Heart Disease Risk
Mon Jul 1, 6:05 PM ET

NEW YORK (Reuters Health) - 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, according to new research.

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 has generated great scientific interest in recent years due to its apparent role in fat metabolism and weight gain. For example, previous research has linked high levels of leptin to an increased risk of cardiovascular disease, while eating fish has been shown to reduce that risk.

"A diet rich in fish is associated with lower plasma leptin, independent of body fat," Dr. Virend K. Somers of the Mayo Clinic in Rochester, Minnesota, and colleagues write.

"These findings may have implications for understanding the reduced cardiovascular risk in subjects on a high-fish diet," they add.

Somers and his 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 one quarter of their total calories from fish, while the other, whose members lived further inland, consumed most of their calories from fruits and vegetables.

Reporting in the rapid access issue of Circulation: Journal of the American Heart Association ( news - web sites), Somers and his colleagues found that male fish-eaters had 2.5 nanograms of leptin per milliliter of blood (ng/mL), less than one quarter of the leptin level of the male vegetarians. Female fish-eaters also had markedly lower leptin levels than their vegetarian peers, with 5 ng/mL versus 12 ng/mL for female vegetarians.

Members of both tribes had virtually identical body mass indices, an indication of obesity that measures weight in relation to height, which suggests that these findings are not influenced by obesity, Virend and his team note. In addition, the investigators found the relationship between leptin and diet persisted even when they accounted for age, body fat, 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 in a statement.

He added that it was not clear whether these results would apply to other people living in different environments. "We don't know if the findings will apply to a semi-overweight, urban-dwelling North American population."

SOURCE: Circulation 2002;10.1161/01.CIR.0000025241.01418.4D.


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