Effects of exercise combined with diet therapy on protein utilization in obese children

PURPOSE: Hypocaloric therapy may adversely affect protein utilization in obese children given that metabolic reactions involving protein, a nutrient essential for growth, are energy-dependent. Because physical activity influences nutrient utilization and may modulate the effects of reduced energy intake, exercise combined with diet therapy may be beneficial with regard to protein metabolism. The primary purpose of this study was to evaluate changes in protein utilization in response to sequential addition of an exercise program to dietary intervention in obese children. METHODS: After a 2-wk baseline period, five subjects aged 8-10 yr reduced energy intake [-2092 to -2510 kJ.d(-1)(-500 to -600 kcal.d(-1))] for 12 wk. A walking program [5 d.wk(-1), 3.2-4.8 km.d(-1) (2-3 miles.d(-1))] was implemented during the final 6 wk of diet therapy. At baseline and after phases I (diet only) and II (exercise and diet) of intervention, 15N-glycine was used to assess protein synthesis (PS), protein breakdown (PB), net turnover (NET = PS - PB), and nitrogen flux (Q). RESULTS: Subjects lost 4.2+/-0.4 kg during the 12-wk intervention period (P < or = 0.05). With diet only, NET decreased (P < or = 0.05) due to a reduction in PS (P < or = 0.05) accompanied by no change in PB. Although PS increased with walking (P < or = 0.05), NET did not return to baseline levels due to a concurrent increase in PB (P < or = 0.05). Changes in PS and PB yielded an increase in Q (P < or = 0.05), a measure of amino acid cycling between protein and free amino acid pools. CONCLUSIONS: These results suggest that exercise offers metabolic benefits for obese children during diet-induced weight loss. Longitudinal studies are needed to assess long-term health outcomes associated with the observed changes in protein utilization.