(P16-16-26) Systematic Review and Meta-Analysis of Fat-free Mass Preservation During Energy Restriction From Randomized Controlled Trials

Objectives: Energy restriction generally elicits weight loss accompanied by losses in fat-free mass (FFM). However, increasing evidence illustrates greater preservation of FFM with higher-protein (HP) vs. normal-protein (NP) diets. We sought to update existing systematic reviews and meta-analyses (SRMAs) of randomized controlled trials (RCTs) concerning the role of increased dietary protein in preserving FFM during energy restriction in adults with overweight/obesity.

Methods: Systematic searches were conducted in PubMed and Web of Science to identify energy restriction RCTs that compared isocaloric diets differing in protein intake (≥1.2, HP vs. 0.8-1.1 g protein/kg body weight per day, NP). Additional inclusion criteria included adults ages 18+ years; study durations of ≥12 weeks; and HP from foods (not supplements). The primary outcome of interest was FFM preservation with secondary assessments of fat mass loss (FM) and weight loss (WL). Subgroup analyses were performed to assess effect modification by study duration, resistance training, and magnitude of energy restriction.

Results: Twenty studies, including 1674 participants (age: 47±2.3 years; BMI: 33.7±0.4 kg/m²), were included in the SRMA. Protein intakes in the HP and NP diets were 1.37±0.04 and 0.81±0.01 g protein/kg per day, respectively. Energy restriction across the studies was, on average, -640±40 kcals/d, and study duration was 4.6±0.5 months. Compared to NP, HP diets led to more favorable changes in weighted mean differences for FFM (+0.195 kg; 95% CI: 0.088, 0.302 kg; p< 0.001) and FM (-0.131 kg; 95% CI: -0.236, -0.026 kg; p=0.01), but not WL (-0.037 kg; 95% CI: -0.138, 0.064 kg; p=0.470). Study duration, resistance training, and magnitude of energy restriction had relatively no effect on FFM, FM, or WL.

Conclusions: HP diets containing ≥1.2 g protein/kg body weight per day elicit greater preservation of FFM during energy restriction in adults with overweight/obesity. These data align with the 2025-2030 Dietary Guidelines for Americans, which recommends a healthy range of protein as 1.2-1.6 g protein/kg body weight per day for weight management in adults with overweight/obesity.

Funding Sources: General Mills Bell Institute of Health & Nutrition. Not official US Army/DoW policy.