Weight management strategies for obese children: Effects of reduced energy intake, diet composition, and exercise on protein utilization

Treatment of pediatric obesity is warranted because excess adiposity is associated with immediate and long-term health risks. However, reduced energy intake may alter energy-dependent metabolic reactions involving protein, a nutrient essential for growth. Diet composition and exercise also are important considerations because these factors modulate nutrient metabolism. The primary purpose of this investigation was to assess the effects of reduced energy intake, diet composition, and exercise on protein turnover in obese children aged eight to 10 years. Following a two-week baseline period, 16 subjects were randomly assigned to one of two dietary intervention groups for six weeks. All subjects reduced energy intake during the intervention period, but the caloric contributions of carbohydrate and fat varied between Groups A ($\le$50% carbohydrate, $\ge$35% fat) and B ($\ge$60% carbohydrate, $\le$25% fat). A subsample of five subjects completed a sequential six-week walking program (5 days/week, 2-3 miles/day) with continued hypocaloric therapy. At baseline and following phases I (diet only) and II (exercise and diet) of intervention, $\sp{15}$N-glycine methodology was used to measure nitrogen flux (Q), protein synthesis (PS), protein breakdown (PB), and net turnover (NET = PS-PB). During phase I, weight loss was greater for Group B ($-$2.8 $\pm$ 0.3 kg) compared to Group A ($-$1.6 $\pm$ 0.4 kg) due to differences in energy balance. Decreases in Q for both groups indicated downregulation of protein turnover with hypocaloric therapy. Because PS and PB declined at similar rates for Group A, NET was maintained at baseline levels. In contrast, PB did not change for Group B, and NET decreased consequent to reduced PS. Changes in protein turnover were dependent on energy balance rather than diet composition. Also, there were no group differences in protein utilization following intervention indicating that diet composition did not affect turnover when ample time was allotted for adaptation to therapy. During phase II, Q increased during weight loss ($-$1.5 $\pm$ 0.2 kg) but NET did not change because both PS and PB were upregulated with walking. Thus, hypocaloric therapy compromised protein metabolism irrespective of diet composition, and exercise had a beneficial effect. Longitudinal studies are needed to characterize health outcomes associated with the observed metabolic responses to therapy.