Why are nutritionally stunted children at increased risk of obesity? Studies of metabolic rate and fat oxidation in shantytown children from São Paulo, Brazil

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Abstract
Background: Previous research suggested that nutritionally stunted children may have increased risk of obesity, but little is known about potential underlying mechanisms. Objective: We sought to test the hypothesis that stunted children have a low metabolic rate and impaired fat oxidation relative to nonstunted children. Design: The subjects were 58 prepubertal boys and girls aged 8–11 y from the shantytowns of São Paulo, Brazil. Twenty-eight were stunted (height-for-age z score <−1.5) and 30 had similar weight-for-height but normal height (height-for-age z score >−1.5). Parents of children in the 2 groups had equivalent height and body mass index values. Fasting and postprandial energy expenditure, respiratory quotient (RQ), and substrate oxidation were measured with indirect calorimetry in a 3-d resident study in which all food was provided and body composition was measured with dual-energy X-ray absorptiometry. Results: Stunted children had normal resting energy expenditure relative to body composition compared with control children (4559 ± 90 and 4755 ± 86 kJ/d, respectively; P = 0.14) and had normal postprandial thermogenesis (2.4 ± 0.3% and 2.0 ± 0.3% of meal load, respectively; P = 0.42). However, fasting RQ was significantly higher in the stunted group (0.92 ± 0.009 compared with 0.89 ± 0.007; P = 0.04) and consequently, fasting fat oxidation was significantly lower (25 ± 2% compared with 34 ± 2% of energy expenditure; P < 0.01). Conclusions: Childhood nutritional stunting is associated with impaired fat oxidation, a factor that predicted obesity in other at-risk populations. This finding may help explain recent increases in body fatness and the prevalence of obesity among stunted adults and adolescents in developing countries.