Metabolic rate and body composition of Pima Indian and Caucasian children.

A low metabolic rate for a given body size and body composition may be a risk factor for body weight gain. Because the prevalence of obesity exceeds 75% in the Pima Indian population, we investigated whether Pima Indian children have a low resting metabolic rate (RMR) when compared with Caucasian children. Body composition (bioelectrical resistance) and RMR were measured in 43 Pima Indian children (22 male/21 female, means +/- SD = 9.9 +/- 1.1 year) and 42 Caucasian children (21 male/21 female, 9.7 +/- 1.2 year). Pima Indian children were taller (p < 0.001), heavier (p < 0.001), and fatter (p < 0.0001) than Caucasian children. Absolute values of RMR were higher in the Pimas than in the Caucasians (p < 0.001), but were similar when adjusted for differences in body size, body composition, and sex. In Pima Indian girls before puberty (< 10 years; n = 8), adjusted values of RMR were negatively correlated with the mean body mass index (BMI) of the parents (r = -0.88; p < 0.005). Inasmuch as resting metabolic rate was not low in Pima children, the data suggest that the major factors in the weight gain of 10-year-old Pima children may be reduced physical activity and/or excess energy intake. However, this study does not exclude the possibility that a low metabolic rate may be a predisposing factor at an earlier age.