Sexual dimorphism in body composition across human populations: associations with climate and proxies for short- and long-term energy supply.

OBJECTIVES: Sexual dimorphism in human stature, physique, and adiposity is well established, but the ecological factors that account for its variability remain unknown. This study aimed to describe population variability in body composition dimorphism, and to test whether annual temperature and proxies for population energy supply accounted for this variability.
METHODS: Data on sex-specific anthropometry (weight, stature, triceps, and subscapular skinfolds) and mean annual temperature were collated for 96 nonindustrialized populations. Lean mass and fat mass were calculated. Sexual dimorphism was expressed in sympercents. Sex-averaged skinfolds and stature were used as proxies for short-term and long-term energy supply, respectively.
RESULTS: All outcomes showed significant mean dimorphism except body mass index. The magnitude of dimorphism was not randomly distributed across global regions, being lowest in African and Asian populations and greatest in Arctic populations. There was a negative correlation across populations between lean mass dimorphism and adiposity dimorphism, independent of temperature. With decreasing temperature, dimorphism in both lean mass and adiposity increased. Dimorphism increased in fatter but not taller populations, independently of temperature.
CONCLUSIONS: The inverse correlation between lean mass dimorphism and adiposity dimorphism indicates a sex-trade-off between these two tissue accretion strategies. At colder temperatures, females invest disproportionately more in adiposity, and males disproportionately more in lean mass. Dimorphism also increased in proportion to proxies for short-term but not long-term energy availability. These findings suggest that phenotypic plasticity contributes to variability in body composition dimorphism, and that the occupation of dimorphic niches regarding reproductive energetics may be important.