METHODS We adopted a counterfactual approach to quantify the excess weight gains beyond normal growth in order to estimate the implicit ‘energy gap'—the accumulated imbalance between energy expenditure relative to caloric intake. Based on CDC growth charts, we estimated weight, height and BMI percentile distributions for cohorts aged 2-4 and 5-9 in the 1988-94 National Health and Nutrition Examination Survey (NHANES; N=7497). Under the counterfactual ‘normal growth only' scenario, we assumed these percentile distributions remained the same as the cohort grows over 10 years. Under this assumption, we mapped their weight and height according to growth charts for ages 12-14 and 15-19 and compared to the corresponding age groups in NHANES 1999-2002; N=4368). The assumption of stable height percentile and of changes in weight and BMI were externally verified with 10 year national cohort data from youth ages 2-4 (National Longitudinal Survey of Labor Market Experience, Youth cohort: N=720).The excess energy accumulation responsible for fueling the shift in weight distribution was subsequently calculated based on the difference between the counterfactual and observed weight gain.

RESULTS Compared with the counterfactual scenario, boys and girls who were 2-4 in NHANES 1988-1994 had gained on average an excess of 1.2 lb. per year in the 10-year period, and those 5-9 an excess 0.7. Assuming that 3500 kcal lead to an average one pound weight gain, these results suggest that an increase in expenditure or a reduction in caloric intake by on average 23 (ages 2-4) or 14 kcal/day (ages 5-9) would have resulted in no such shift in weight distribution. Therefore, potential interventions that counterbalance the energy gap could include walking an extra mile everyday (roughly 35 kcal burned for a child weighing 70 lb) or reducing consumption of sugared beverages. We assessed average daily consumption of sugar-sweetened beverages among children age 2-12 in the two NHANES studies and found that intake increased by roughly 27 kcal per day over this period (p=0.0013).

CONCLUSION Quantifying the energy imbalance responsible for recent changes in weight among children provides a salient target for implementing population interventions. Reducing intake of sugar-sweetened beverages is likely to be an important strategy.