The Effects of 10 Months of Exercise on Circulating Ketone Body Concentration and Oxidative Capacity: A Secondary Analysis of a Randomized Controlled Trial

Background: Exercise offers many benefits for children, but the role of alternative fuel sources, such as ketones, is understudied. Skeletal muscle, particularly type I fibers, uses ketones, and aerobic exercise enhances oxidative capacity. Indeed, the effect of exercise on ketone levels in non-athletes and adolescents is largely unknown. Thus, the purpose of the present study sought to examine the relationship between long term exercise regimens on ketone concentration while assessing the simultaneous effects of puberty. It was hypothesized that physical activity would reduce circulating ketone levels. Methods: 148 healthy young non-Hispanic Black females participated in a 10-month moderate-to-vigorous aerobic exercise intervention. Circulating ketone concentrations were measured using nuclear magnetic resonance, and pubertal staging was assessed by Tanner staging. Body fat was measured using dual-energy X-ray absorptiometry, Body Mass Index (BMI) percentiles were calculated from age and sex-specific growth charts provided by the Centers for Disease Control and Prevention, and maximal oxygen consumption assessed oxidative capacity. Results: Participants were 9.5 ± 0.9 years old at baseline with BMI percentiles of 69.9 ± 29.3% and body fat of 28.7 ± 12.1%. Breast development was not correlated with ketone levels at baseline (r= 0.18; p= 0.26). Maximal oxygen consumption was higher in the exercise group compared to controls(mean= 28.9 vs. 26.4 mL/kg/min, p=0.022) after the exercise regimen. Similarly, the exercise group had significantly lower ketone concentrations than the control after the exercise regimen (mean= 170.2 vs. 216.7 μM, p = 0.030). The differences between groups for maximal oxygen consumption and ketone concentration were significant even after controlling for BMI percentile and pubertal staging. Conclusion: Exercise improves oxidative capacity and reduces ketone levels in young girls. This finding highlights the importance of physical activity programming and recognizes a previously undescribed effect of exercise on metabolism in children. This study was funded by the NIH (Grant HL64972). The funding agency did not play a role in the study design. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.