Prediction of fat-free mass using bioelectrical impedance analysis in young adults from five populations of African origin.

BACKGROUND/OBJECTIVES: Bioelectrical impedance analysis (BIA) is used in population and clinical studies as a technique for estimating body composition. Because of significant under-representation in existing literature, we sought to develop and validate predictive equation(s) for BIA for studies in populations of African origin. SUBJECTS/METHODS: Among five cohorts of the Modeling the Epidemiologic Transition Study, height, weight, waist circumference and body composition, using isotope dilution, were measured in 362 adults, ages 25-45 with mean body mass indexes ranging from 24 to 32. BIA measures of resistance and reactance were measured using tetrapolar placement of electrodes and the same model of analyzer across sites (BIA 101Q, RJL Systems). Multiple linear regression analysis was used to develop equations for predicting fat-free mass (FFM), as measured by isotope dilution; covariates included sex, age, waist, reactance and height(2)/resistance, along with dummy variables for each site. Developed equations were then tested in a validation sample; FFM predicted by previously published equations were tested in the total sample. RESULTS: A site-combined equation and site-specific equations were developed. The mean differences between FFM (reference) and FFM predicted by the study-derived equations were between 0.4 and 0.6 kg (that is, 1% difference between the actual and predicted FFM), and the measured and predicted values were highly correlated. The site-combined equation performed slightly better than the site-specific equations and the previously published equations. CONCLUSIONS: Relatively small differences exist between BIA equations to estimate FFM, whether study-derived or published equations, although the site-combined equation performed slightly better than others. The study-derived equations provide an important tool for research in these understudied populations.

Energy expenditure in young adult urban informal settlement dwellers in South Africa.

Obesity prevalences are increasing in industrialized and developing countries. As a pilot for a comparative study of physical activity and weight change, we assessed energy expenditure (EE) in young black South African adults living in an urban informal settlement. Total EE (TEE) was assessed using doubly labeled water, activity EE (AEE) and activity patterns by accelerometry and body composition by isotope dilution. Twenty young women and eight men were enrolled. Over 50% of the women and no men were obese (mean BMI 31.0 and 21.6 kg/m(2), respectively). Women had significantly lower TEE and AEE after adjustment for body size, as well as lower levels of moderate and vigorous activity. Neither TEE nor AEE was associated with BMI or percent body fat, whereas percent time in vigorous activity was modestly negatively associated with adiposity. These data add to the small literature on EE and activity among populations undergoing epidemiologic transitions.

Total daily energy expenditure in black and white, lean and obese South African women.

BACKGROUND/OBJECTIVES: In South Africa (SA), the prevalence of obesity in women is 56%, with black women being most at risk (62%). Studies in the United States have demonstrated ethnic differences in resting (REE) and total daily energy expenditure (TDEE) between African American (AA) and their white counterparts. We investigated whether differences in EE exist in black and white SA women, explaining, in part, the ethnic obesity prevalence differences. SUBJECTS/METHODS: We measured REE, TDEE and physical activity EE (PAEE) in lean (BMI <25 kg m(-2)) and obese (BMI >30 kg m(-2)) SA women (N=44, 30+/-6 year). REE, TDEE, PAEE and total awake EE were measured during a 21 h stay in a respiration chamber. RESULTS: Black and white subjects within obese and lean groups were not significantly different for age, mass, BMI and % body fat. However, fat-free mass (kg FFM) was consistently lower in the black women (P<0.01) in both weight groups. After adjusting EE measurements for differences in FFM, REE was not significantly different for either body weight or ethnicity, although 24 h TDEE (kJ) was significantly greater in the obese women (P<0.01) and white women (P<0.05). Total awake non-PAEE was not significantly different for either groups, while total awake time was only significantly lower for the lean groups (P<0.01). Total PAEE (kJ min(-1)) was significantly lower in the lean (P<0.001) and black groups (P<0.01). CONCLUSIONS: In this sample of matched, lean and obese, black and white SA women, differences in TDEE were largely explained by ethnic differences in PAEE, and were not as a result of ethnic differences in REE.