IS A LOW LEPTIN CONCENTRATION, A LOW RESTING METABOLIC-RATE, OR BOTH THE EXPRESSION OF THE THRIFTY GENOTYPE - RESULTS FROM MEXICAN PIMA-INDIANS

Background: The high prevalence of obesity and type 2 diabetes in some populations is believed to be the expression of a ''thrifty genotype, '' which conferred survival advantages during periods of harsh environ mental conditions, but has become a liability in industrialized enviro nments of abundance. Low plasma leptin concentrations and a low metabo lic rate may be the phenotypic expression of this genotype. Objective: We hypothesized that plasma leptin concentrations and resting metabol ic rate would be lower in Mexican Pima Indians not yet exposed to an a ffluent lifestyle than in non-Pima Mexicans living in the same environ ment. Design: We studied 208 nondiabetic Pima Indians (105 women and 1 03 men) living a traditional lifestyle in a remote, mountainous area o f northwest Mexico and 183 nondiabetic non-Pima Mexicans (90 women and 93 men) living in the same environment. A subset of 40 (17 women and 23 men) Pima Indians and 40 (19 women and 21 men) non-Pima Mexicans wa s selected for studies of energy metabolism with a ventilated-hood sys tem. Results: Leptin concentrations were strongly correlated with perc entage body fat in both groups (r = 0.83, P < 0.0001). There was no si gnificant difference in plasma leptin concentration between groups in absolute value (P = 0.90) or after adjustment for percentage body fat, waist circumference, age, and sex (P = 0.40). Similarly, there was no significant difference in resting metabolic rate between groups in ab solute value (P = 0.27) or after adjustment for fat-free mass (P = 0.3 2). Conclusions: These results do not support the hypothesis that hypo leptinemia, a relatively low resting metabolic rate, or both are expre ssions of the thrifty genotype.