Relative contribution of energy intake and energy expenditure to childhood obesity: a review of the literature and directions for future research

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Abstract
Understanding the relative importance of overconsumption and physical inactivity to excess weight gain among children and adolescents can contribute to the development and evaluation of interventions and policies to reduce childhood obesity. However, whether energy intake or expenditure is the dominant contributor to childhood obesity is a subject of debate. To date, no study has systematically reviewed the literature on this subject. We searched PubMed and Ovid Medline (January 1970 to January 2010) for potentially relevant English-language abstracts and obtained full-text articles for the abstracts, which passed the initial inclusion-exclusion criteria. Reference lists of full-length articles were hand searched to identify additional studies potentially relevant for inclusion. Relevant studies were characterized into one of the following three categories: cross-sectional studies with a nationally representative sample, cross-sectional studies among population subgroups and longitudinal studies. This review identified 26 studies examining factors related to energy intake, energy expenditure and obesity among children and adolescents. Cross-sectional and longitudinal studies suggest that the primary determinant of energy imbalance at both the population and the individual levels is not definitive. Our findings further suggest that there is wide variation in data quality between studies. Future research in this area should aim to improve the accuracy of measures of energy intake, expenditure and their net balance over time; capitalize on under-utilized, non-traditional data sources, which have not been widely used; use modeling techniques to synthesize studies of shorter follow-up period and different outcome measures; and examine the unique determinants of energy imbalance among demographic groups at higher risk for obesity. On the basis of the current evidence, there is no consensus on the main driver of secular trends on weight gain among US children and adolescents. More research and better methods are needed to identify the relative contribution of energy intake and energy expenditure to obesity in the pediatric population.