Differences in body composition between Tongans and Australians: time to rethink the healthy weight ranges?

Objective: The prevalence of obesity varies considerably between countries when compared using the common international standard. This study investigated body size and body composition in Tongan and Australian Caucasian adults. Design: Cross-sectional comparative study. Subjects: A total of 543 Tongans and 393 Australians. Measurements: Weight, height, waist and hip circumference, four skinfolds, midarm circumference, elbow breadth, and body composition by bioelectrical impedance using sex- and ethnic-specific regression equations. Results: Tongan women (mean body mass index (BMI)+/- s.e.=32.6 +/-0.4kg/m(2)) were larger than Australian women (BMI=25.8 +/-0.4 kg/m(2)), with more fat-free mass (FFM; 52.2 +/-0.4; 42.6 +/-0.3 kg), fat mass (37.1 +/-0.7; 26.6 +/-0.8 kg) and percentage body fat (%fat) (40.5 +/-0.4; 37.0 +/-0.5%), respectively. Tongan men also had higher BMI (Tongan=30.3 +/-0.3 kg/m(2); Australian =26.5 +/-0.3 kg/m(2)), FFM (70.2 +/-0.5; 62.3 +/-0.6 kg) and fat mass (23.5 +/-0.6; 20.7 +/-0.7kg). When compared with Australians within the same BMI range, Tongans had significantly higher FFM, elbow width, midarm muscle area and significantly lower %fat. The %fat at BMIs of 25 and 30 kg/m(2) in Australian women was equivalent to the %fat found in Tongan women at 28.8 and 35.1 kg/m(2), respectively. BMIs of 25 and 30 kg/m(2) in Australian men corresponded with 27.5 and 35.8 kg/m(2) in Tongan men. Skinfold thicknesses, waist, hip and WHR measurements suggested differences in fat distribution and body shape between ethnic groups, particularly in women. Conclusion: These results suggest that the standard healthy weight ranges recommended for international use may not be appropriate standards for use in the Tongan population.