Diagnostic Comparison of Tri-Ponderal Mass Index (Tmi) and Body Mass Index (Bmi) in Estimating Overweight and Obesity in South African Children
A recent study has shown that tri-ponderal mass index (TMI) could be a more accurate diagnostic criterion than body mass index (BMI) in estimating body fat levels in adolescents (Peterson et al., 2017). To test this hypothesis, the prevalence of overweight and obesity in South African children based on the TMI and BMI was comparatively examined. Also analysed was the relationship of selected body composition variables with TMI and BMI in the children.A cross-sectional survey of 1361 (boys: n=683; girls: n=678) school children aged 9-13 years was undertaken. The children’s height, body weight, and skinfolds were assessed using the procedures of International Society for the Advancement of Kinanthropometry (ISAK). Age- and sex-related measurements of body weight, WHtR (waist-to-height ratio), WHR (waist-to-hip ratio), TSKF (triceps skinfold), SSKF (sum of skinfolds), ΣSKF (sum of skinfold), BMI and TMI were taken. TMI and BMI for age was used to classify the children according to weight categories. Ethical procedures of Helsinki declaration involving human participants were observed. Descriptive statistics, Spearman’s correlations and multiple linear regression analyses were undertaken with the probability level set at p ≤ 0.05.Overall prevalence of overweight and obesity based on TMI and BMI classifications among the children were as follows: Boys: 7.3%, 2.6%; 2.2%, 0.7%; Girls: 4.0%, 1.0%; 1.8%; 0.6%. The results also showed that body weight, WHtR, WHR, TSKF, SSKF and ΣSKF significantly correlated with TMI (r = 0.40, p < 0.001; r = 0.73, p < 0.001; r = -0.09, p < 0.001; r = 0.50, p < 0.001; r = 0.51, p < 0.001 and r = 0.52, p < 0.001) and BMI (r = 0.81, p < 0.001; r = 0.59, p < 0.001; r = -0.22, p < 0.001; r = 0.63, p < 0.001; r = 0.67, p < 0.001 and r = 0.66, p < 0.001). The regression analysis revealed that body weight, WHtR, WHR, TSKF, SSKF and ΣSKF accounted for 65 and 85 percent of the variance in the children’s TMI (R2 = 0.647, F (6, 1354) = 413.977, p < 0.001) and BMI (R2 = 0.851, F(6, 1354) = 1288.218, p < 0.001), respectively. Tri-ponderal mass index revealed strikingly higher incidence of overweight and obesity in the South African boys and girls than BMI. Future studies are needed to clarify the sensitivity of TMI over the BMI in quantifying the prevalence of overweight and obesity in children and adolescents.
Keywords - Tri-ponderal mass index, BMI, Children, South Africa.