(P24-01-26) Effects of Aerobic and Resistance Training on Body Composition in Young Men With Normal Weight Obesity

Objectives: Normal weight obesity (NWO) is a phenotype characterized by normal weight body mass index (BMI) but increased body fat percentage (BF%). Individuals with NWO have increased risk of cardiometabolic disease. Little is known about treatment of NWO. The objective of this study is to determine whether aerobic or resistance exercise is more effective for improving body composition in young men with NWO.

Methods: In this trial, 48 young men aged 18-39 years were recruited: 16 normal-weight lean (NWL; 18.5-24.9 kg/m2, BF% < 20%), 16 NWO (BMI 18.5-24.9 kg/m2, BF% ≥25%), and 16 with traditional obesity (OB; BMI ≥30 kg/m2, BF% ≥25%). Participants completed baseline testing that included a DXA body composition scan to determine absolute fat and lean mass (kg), relative fat and lean mass (%), and visceral adipose tissue (VAT). The NWO group was then randomized to complete aerobic or resistance exercise training for 12 weeks. Following the intervention, NWO participants repeated baseline testing.

Results: BMI was similar between NWL (22.8 ± 2.5 kg/m²) and NWO (23.1 ± 0.8 kg/m²), and significantly higher in OB (34.5 ± 4.1 kg/m²) than in both groups (p < 0.0001). BF% (NWL: 19.8 ± 2.9%, NWO: 29.1 ± 2.0%, OB: 35.1 ± 5.0%), VAT (NWL: 329.4 ± 42.9 g/cm³, NWO: 461.3 ± 100.2 g/cm³, OB: 719.1 ± 202.7 g/cm³), and lean mass (NWL: 76.5 ± 2.8%, NWO: 67.4 ± 1.9%, OB: 61.8 ± 5.0%) differed significantly among all groups (all p < 0.0001). After the 12-week exercise intervention in the NWO group, aerobic training significantly reduced BF% (-2.8%; p = 0.01), whereas resistance training did not (-1.1%; p = 0.32). Absolute body fat at follow-up was significantly lower in the aerobic group compared with the resistance group (-4.1 kg; p = 0.006). Relative lean mass significantly increased after aerobic training (+2.8%; p = 0.02), but not after the resistance training (+1.8%; p = 0.10). In contrast, absolute lean mass at follow-up was greater in the resistance group compared with the aerobic group (+6.4 kg; p = 0.01).

Conclusions: These findings suggest aerobic exercise may be more effective for improving relative distribution of fat and lean mass in young men with NWO. In contrast, the resistance training group showed a greater increase in absolute lean mass post-training.

Funding Sources: American Heart Association Institutional Research Enhancement Award (25AIREA1377732)