Intramyocellular lipid use is altered with exercise in males with childhood-onset obesity despite no differences in substrate oxidation.

Objective: Compared to adulthood-onset obesity (AO), those with childhood-onset obesity (CO) are at greater risk of metabolic disease. However, the differences between these two obesity phenotypes are not clear. The aim of this study is to investigate how the age of obesity onset (CO vs. AO) affects the use of intramyocellular (IMCL) and extramyocellular (EMCL) lipids in response to exercise.

Methods: Males with CO (n = 5) and AO (n = 5) were recruited. At the first study visit, body composition was measured via dual-energy x-ray absorptiometry (DEXA). Energy expenditure and substrate oxidation were measured via indirect calorimetry. Participants were provided with standardized meals for 3 days prior to the exercise study visit. At the exercise study visit, IMCL and EMCL were measured via magnetic resonance spectroscopy (MRS) before and after 90-minutes of moderate intensity cycling with indirect calorimetry.

Results: Substrate oxidation at rest and during exercise was not different between groups. Post-exercise, a decrease in IMCL was observed in the AO group that was not demonstrated in the CO group. There were no changes in EMCL post-exercise in either group.

Conclusions: This was the first study to compare the effects of exercise on IMCL and EMCL use in males with CO and AO. The decreases in IMCL of the AO group is similar with those observed in the literature in lean individuals. We made the novel observation that with moderate intensity cycling, males with CO do not appear to use IMCL as effectively as those with AO, suggesting perturbations in IMCL metabolism.