CONTEXT

Exercise reduces adiposity, but its influence on bone marrow fat fraction (BMFF) is unknown; nor is it known whether a reduction in liver fat content mediates this reduction.

OBJECTIVES

This work aimed to determine whether incorporating exercise into a lifestyle program reduces the lumbar spine (LS) BMFF and to investigate whether changes in liver fat mediate any such effect.

METHODS

Ancillary analysis of a 2-arm, parallel, nonrandomized clinical trial was conducted at primary care centers in Vitoria-Gasteiz, Spain. A total of 116 children with overweight/obesity were assigned to a 22-week family-based lifestyle program (control group [n = 57]) or the same program plus an exercise intervention (exercise group [n = 59]). The compared interventions consisted of a family-based lifestyle program (two 90-minute sessions/month) and the same program plus supervised exercise (three 90-minute sessions/week). The primary outcome examined was the change in LS-BMFF between baseline and 22 weeks, as estimated by magnetic resonance imaging. The effect of changes in hepatic fat on LS-BMFF were also recorded.

RESULTS

Mean weight loss difference between groups was 1.4 ± 0.5 kg in favor of the exercise group. Only the children in the exercise group experienced a reduction in LS-BMFF (effect size [Cohen d] -0.42; CI, -0.86 to -0.01). Importantly, 40.9% of the reductions in LS-BMFF were mediated by changes in percentage hepatic fat (indirect effect: β=-0.104; 95% CI, -0.213 to -0.019). The effect of changes in hepatic fat on LS-BMFF was independent of weight loss.

CONCLUSION

The addition of exercise to a family-based lifestyle program designed to reduce cardiometabolic risk improves bone health by reducing LS-BMFF in children with overweight or obesity. This beneficial effect on bone marrow appears to be mediated by reductions in liver fat.