Impact of Different Exercise Modalities on Visceral Adipose Tissue in Normal Weight and Low-Overweight Individuals: A Systematic Review and Meta-Analysis.

The "thin outside, fat inside" (TOFI) phenotype, also termed normal weight obesity (NWO), describes individuals with normal body mass index (BMI) but elevated visceral adipose tissue (VAT). Individuals at the lower boundary of the overweight range may also present with excess VAT despite near-normal BMI. Although exercise is widely recommended to improve body composition, its effects on VAT in these populations remain unclear. This review evaluated the effects of different exercise modalities on VAT in adults with BMI ≤27 kg/m2. A systematic search of PubMed, Scopus, and Web of Science was conducted for studies published between January 1999 and July 2024. Eligibility was determined at the study level based on reported mean BMI (≤27 kg/m2). Studies including aerobic, resistance, combined, or interval training interventions with VAT assessed via computed tomography, magnetic resonance imaging, or dual-energy X-ray absorptiometry were included. Between-group (controlled) and within-group (single-arm or pre-post) analyses were conducted separately using standardized mean differences (SMD). The protocol was registered on OSF (10.17605/OSF.IO/3DCXJ). Thirteen studies (n = 354 participants) were included. Between-group analysis demonstrated a significant reduction in VAT favoring exercise (SMD = -1.590; 95% CI: -2.283 to -0.898; p < 0.001), with substantial heterogeneity (I2 = 86.4%). Aerobic training showed the most consistent effects, while interval training was also associated with significant reductions based on a limited number of studies. Longer intervention duration (>5 months) was associated with greater effects. Within-group analyses showed a similar direction of effect but did not reach statistical significance. Sensitivity analyses indicated that results were directionally robust but partially influenced by high-impact studies. Exercise is associated with reductions in VAT in adults with normal BMI and those at the lower boundary of the overweight range. However, the certainty of evidence is low due to methodological limitations, heterogeneity, and potential bias. Greater emphasis should be placed on findings from controlled studies. Further well-designed randomized controlled trials are needed to confirm these findings and clarify the roles of different exercise modalities and intervention characteristics.