Author(s): MABALOT, M., RYAN, L., PATERSON, C., ELLISON, C., WEELDREYER, N., LIU, Z., GAESSER, G., SIDDIQUI, M., PAN, J., MACNAMARA, J., ANGADI, S., Institution: UNIVERSITY OF VIRGINIA, Country: UNITED STATES, Abstract-ID: 1725

INTRODUCTION:
Overweight and obesity are globally prevalent, and 42% of adults attempt weight loss (WL). Adults lose fat-mass (FM) and fat-free mass (FFM) during WL, but WL recidivism rates are high, approaching ~100% at 5 years (1,2). However, changes in body composition (FM, FFM and lean body mass (LBM)) during weight regain (WR) have not been systematically examined. Previous reviews are confounded by short follow-up times, inconsistent definitions of WR, and differences in measurement techniques. Therefore, this study aimed to synthesize data from randomized controlled WL trials using direct measures of body composition to determine the implications for body composition during WR.
METHODS:
Electronic databases (Embase, PubMed, Scopus, CINAHL) were searched through June 2025. Thirty-six studies quantifying changes in body composition across WL interventions of ≥12 weeks and follow-up periods of ≥6 months were identified. Data were analyzed with a three-level restricted maximum likelihood estimation random-effects model with robust variance estimation. Subgroup analyses investigated whether WR differed by intervention type, and meta-regression was used to assess the effect of follow-up time on WR. Interventions were grouped as diet, exercise, diet + exercise, and non-intervention controls. Data are reported as mean difference (MD) with 95% confidence intervals (95%CI) for body weight (BW), FM, FFM, and LBM.
RESULTS:
Across 4,022 participants (female n=2,600), WR was 2.99kg (95%CI: 1.93, 4.05; p<0.001). This regain consisted of 2.56kg FM (95%CI: 1.74, 3.37; p<0.001), 0.27kg FFM (95%CI: -0.06, 0.61; p=0.107), and 0.18kg LBM (95%CI: -0.15, 0.50; p=0.251). In the subgroup analysis, control and intervention groups did not differ from each other (BW: F=0.22, p=0.881; FM: F=0.45, p=0.723; FFM: F=1.02, p=0.439; or LBM: F=1.02, p=0.530). The meta-regression by follow-up time did not reveal an effect of follow-up time for BW (F=36.0, p=0.061), FM (F=18.7, p=0.090), FFM (F=1.20, p=0.338), or LBM (F=31.9, p=0.164).
CONCLUSION:
Overall, WR principally reflects the recovery of FM, not FFM or LBM. Based on the subgroup analyses, active interventions such as diet, exercise, or diet + exercise were no different from non-intervention controls during the WR period. The effects of follow-up time on BW and FM approached significance (p<0.1), which may suggest a time-dependent trend toward greater regain of these variables. This systematic review and meta-analysis underscores the predominance of FM regain during WR. These data may have implications for cardiometabolic health and for weight regain following cessation of weight loss medications.

References:
1. Prado CM., et al. (2024). Muscle matters: the effects of medically induced weight loss on skeletal muscle. Lancet Diabetes Endocrinol. 12(11):785-787.
2. Dansinger ML., et al. (2007). Meta-analysis: the effect of dietary counseling for weight loss. Ann Intern Med. 3;147(1):41-50.