Normal-weight obesity and low muscle mass in college students: Associations with physical activity and bone health.

OBJECTIVE

Body mass index (BMI) may fail to identify cardiometabolic risk in young adults with unfavorable body composition. This study examined associations between low skeletal muscle mass, lifestyle behaviors, and bone health in normal-weight college students, defined as those with a BMI in the normal range (18.5-24.9 kg/m2).

PARTICIPANTS

Eighty-seven students (85% female; mean age 20.9 years) with normal-range BMI from California Polytechnic State University, San Luis Obispo.

METHODS

Dual-energy X-ray absorptiometry assessed body composition and bone mineral density. Low muscle mass was defined as appendicular lean mass index z-score ≤ -1.0. Multivariable regression examined predictors of muscle mass and bone outcomes.

RESULTS

Twenty-two percent exhibited low muscle mass despite normal BMI. Physically active students had 93% lower odds of low muscle mass compared to inactive students (OR = 0.07, 95% CI: 0.01; 0.54, p = .010). Physical activity (β = 0.85, 95% CI: 0.35; 1.36, p = .001) and meal skipping (β = -0.71, 95% CI: -1.23; -0.20, p = .007) independently predicted bone density. Despite normal BMI, 61% had elevated triglycerides.

CONCLUSIONS

BMI-based screening may underestimate health risk. Body composition and lifestyle assessment may improve early identification.