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Obesity is nearly twice as common in older black women as it is in white women. This difference has not been found to be due totally to environmental influences, suggesting inherent metabolic and/or physiologic differences between races. The racial dissimilarities may be the result of differences in the expression of obesity-regulating genes. Leptin, the product of the obesity gene, is thought to play a role in the regulation of body weight. It is not yet understood how leptin affects energy expenditure. Nicklas and associates examined racial differences in leptin levels and investigated whether the relationships of leptin to body composition and resting metabolism differ between black women and white women.

Fifty-seven sedentary, postmenopausal, obese women over 50 years of age (28 black women and 29 white women) were evaluated after a 12-hour fast. Body composition, maximal aerobic capacity, resting metabolism and circulating leptin levels were determined. Resting energy expenditure was measured using indirect calorimetry.

Black women had a significantly lower leptin level than white women. Resting energy expenditure did not differ between the groups. These findings suggest racial differences in the expression of leptin by adipose tissue and its role in the regulation of resting energy expenditure.

In mice, leptin influences weight by decreasing food intake and increasing resting and physical energy expenditures. Previous studies have demonstrated that the lower leptin levels in younger black women may contribute to lower resting and physical energy expenditures. In this study, the patients were older and did not show the same effect of leptin on resting energy expenditure.

The authors conclude that obese postmenopausal black women have 20 percent lower plasma leptin levels than obese postmenopausal white women. The concentration of circulating leptin was an independent predictor of resting energy expenditure in black women but not in white women. Future studies of the role of leptin in modifying obesity need to be race-specific because of these racial variations.

RICHARD SADOVSKY, M.D.

Nicklas BJ, et al. Racial differences in plasma leptin concentrations in obese postmenopausal women. J Clin Endocrinol Metab 1997;82:315-7.