Sex differences in the prevalence of obesity in rural African adolescents

OBJECTIVE: To investigate the prevalence and gender differences in obesity in rural African adolescents. DESIGN: Cross-sectional analysis of a mixed-longitudinal study. SUBJECTS: Four hundred and forty-seven rural African adolescents (190 females; 257 males) aged 7.0-18.9y. MEASUREMENTS: Anthropometric measurements of height, weight, and skinfolds at the bicep (BCP), tricep (TRCP), subscapular (SSCP) and suprailiac (SPIL) sites and derived ratios of fat distribution including trunk:limb ratios (SSTB = (SSCP + SPIL)/(TRCP + BCP) and ST = SSCP/TRCP), and the upper:lower truncal ratio (TRUNK = SSCP/SPIL). Obesity was defined as (1) a BMI greater than the NHANES III 85% centile or (2) the sum of TRCP and SSCP skinfolds greater than the NHANES III 85% centile. RESULTS: Skinfold measures were significantly greater in females throughout the age range but remarkably greater divergence was apparent after mean menarcheal age of 14.03y (s.d.=1.25). Centralization of body fat was consistently greater in males but only significantly so after 14y of age for the ST ratio. Obesity, defined by BMI or sum of skinfolds, was greatest in females following menarche reaching a maximum of 16.7% by BMI and 11.1% by sum of skinfolds, and almost non-existent in males. CONCLUSIONS: Increased prevalence of obesity in African females did not occur throughout adolescence but was linked to the timing of menarche. Increased fatness and obesity appears to be a post-menarcheal phenomenon probably caused by the hormonal changes leading to and following first menstruation.