Effects of Calorie Restriction With and Without Strength, Endurance or Mixed Training on Fat-Free and Skeletal Muscle Mass in Overweight or Obese Individuals-A Systematic Review With Pairwise Meta-Analysis and Network Meta-Analysis of Randomized Controlled Studies

AIMS: Calorie restriction (CR) reduces both fat mass and fat-free mass (FFM), particularly skeletal muscle mass (SMM), which is essential for cardiometabolic health and preventing frailty. This study compares CR alone versus CR plus exercise (EX) on FFM and SMM in overweight/obese patients and examines the effects of different training modes. METHODS: A systematic literature search was conducted in the PubMed and Web of Science databases. After screening, 34 randomized controlled trials were included in the final analyses, involving a total of 1455 participants. RESULTS: A random-effects model showed a significant effect of EX on FFM, with a pooled mean difference favouring CR combined with EX over CR alone (mean difference (MD) = +0.87 kg; 95% confidence interval (CI): +0.59, +1.16 kg; p ≤ 0.001). On average, EX prevented nearly half of FFM loss (45.7%). While subgroup testing found no significant differences between training modes, point estimates suggested greater benefits when the intervention included strength training. An additional network meta-analysis, conducted to account for the repeated use of the same control group in multi-arm studies, revealed that mixed training yielded the largest effect (MD = +1.20 kg, 95% CI: +0.67, +1.73 kg; p < 0.001, P-score = 0.93), followed by strength training (MD = +0.83 kg, 95% CI: +0.17, +1.49; p = 0.013; P-score = 0.66), while endurance training fell just short of statistical significance (MD = +0.51 kg, 95% CI: -0.04, +1.05; p = 0.067; P-score = 0.41). Only two studies reported SMM, both indicating muscle-preserving effects of EX. CONCLUSIONS: Exercise training is very effective in reducing FFM loss during CR. The present study provides valuable new insights for optimizing weight loss strategies. TRAIL REGISTRATION: CRD420251058428.