Plasma leptin concentrations in Pima Indians living in drastically different environments

OBJECTIVE - Plasma leptin, an important signal for the regulation of energy stores, is known to be influenced by many hormonal factors, but may also b e affected by behavioral and environmental factors. The purpose of this stu dy was to investigate the impact of lifestyle (diet composition, level of p hysical activity) on plasma leptin concentrations among Pima Indians living in drastically different environments. RESEARCH DESIGN AND METHODS - We studied 224 Mexican Pima Indians (115 wome n, 109 men) living a traditional lifestyle in a remote, mountainous area of northwest Mexico and 418 U.S. Pima Indians (281 women, 137 men) living a N orth American lifestyle on the Gila River Indian Reservation in Arizona. We hypothesized that the absolute value of leptin would be lower in Mexican P ima Indians because of their lower percent body fat, but could be further i nfluenced by their lifestyle, Independent of body composition. RESULTS - Leptin concentration (enzyme-linked immunosorbent assay [ELISA]) was strongly correlated with percent fat (bioimpedance) in Mexican Pima Ind ians (r = 0.83, P < 0.0001) and U.S. Pima Indians (r = 0.86, P < 0.0001). A mong U.S. Pima Indians, independent of percent fat, subjects with type 2 di abetes had lower leptin than nondiabetic subjects (difference = 6.9 +/- 1.0 ng/ml, P < 0.002). Among nondiabetic subjects, Mexican Pima Indians had lo wer absolute leptin concentrations than U.S. Pima Indians, but higher after adjustment for percent body fat, waist circumference, age, and sex. In a s ubset of 70 pairs of subjects matched for sex and percent body fat, leptin concentration was 4.4 +/- 1.0 ng/ml (P < 0.0001) higher in Mexican Pima Ind ians versus U.S. Pima Indians. CONCLUSIONS - These results suggest that independent of body composition, l eptin concentration may be increased by environmental factors, such as a hi gh-carbohydrate diet and a high lever of physical activity.