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

Background: Previous research suggested that nutritionally stunted children may have increased risk of obesity, but little is known about potential un derlying mechanisms. Objective: We sought to test the hypothesis that stunted children have a lo w metabolic rare and impaired fat oxidation relative to nonstunted children . Design: The subjects were 58 prepubertal boys and girls aged 8-11 y from th e shantytowns of Sao Paulo, Brazil. Twenty-eight were stunted (height-for-a ge z score <-1.5) and 30 had similar weight-for-height but normal height (h eight-for-age z score >-1.5). Parents of children in the 2 groups had equiv alent height and body mass index values. Pasting and postprandial energy ex penditure, respiratory quotient (RQ), and substrate oxidation were measured with indirect calorimetry in a 3-d resident study in which all food was pr ovided and body composition was measured with dual-energy X-ray absorptiome try. 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). Howev er, fasting RQ was significantly higher in the stunted group (0.92 +/- 0.00 9 compared with 0.89 +/- 0.007, P = 0.04) and consequently, fasting fat oxi dation 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. T his finding may help explain recent increases in body fatness and the preva lence of obesity among stunted adults and adolescents in developing countri es.