Exercise training prevents 45.7% of fat-free mass loss during calorie restriction in overweight and obese individualsExercise helps people with obesity keep muscle during weight loss

This meta-analysis evaluated the impact of different exercise modalities on fat-free mass (FFM) and skeletal muscle mass (SMM) in a population of 1,455 overweight or obese individuals undergoing calorie restriction (CR). The study aimed to determine if adding exercise (EX) to CR protocols could mitigate the loss of lean tissue often associated with caloric deficits. The analysis included various training modes, including strength, endurance, and mixed training.

The primary outcome was the preservation of fat-free mass (FFM). The meta-analysis revealed that exercise prevented nearly half of the FFM loss typically seen in calorie restriction alone, specifically a 45.7% reduction in FFM loss. When comparing CR plus EX to CR alone using a random-effects model, there was a significant effect favoring the combined intervention with a mean difference (MD) of +0.87 kg (95% CI: +0.59, +1.16 kg; p ≤ 0.001).

A network meta-analysis was conducted to compare specific training modes. Mixed training showed the largest effect among all modalities, with an MD of +1.20 kg (95% CI: +0.67, +1.73 kg; p < 0.001; P-score = 0.93). Strength training was identified as the second most effective mode, yielding an MD of +0.83 kg (95% CI: +0.17, +1.49; p = 0.013; P-score = 0.66). Endurance training showed a positive trend but fell just short of statistical significance with an MD of +0.51 kg (95% CI: -0.04, +1.05; p = 0.067; P-score = 0.41).

Secondary outcomes included skeletal muscle mass (SMM). While only two studies reported specific data for SMM, both indicated that the addition of exercise provided muscle-preserving effects during calorie restriction. No specific numerical values or confidence intervals were available for these secondary results.

Regarding safety and tolerability, no data were reported concerning adverse events, serious adverse events, discontinuations, or general tolerability. The study highlights a clear clinical distinction between caloric deficit alone and caloric deficit combined with structured exercise in the context of muscle preservation.

These findings contribute to the understanding of how to manage body composition during weight loss. While calorie restriction is a standard intervention for obesity, these results suggest that adding mixed or strength training provides superior protection against lean mass loss compared to endurance training alone. The significant difference between mixed training (MD +1.20 kg) and endurance training (MD +0.51 kg) suggests specific programming may influence outcomes.

Methodological limitations include the fact that only two studies reported SMM, limiting the ability to draw broad conclusions on skeletal muscle specifically. Furthermore, results for specific training modes were derived from a network meta-analysis to account for shared controls across different study designs. Clinical implications suggest that clinicians should recommend combined exercise and calorie restriction rather than caloric restriction alone to preserve fat-free mass in patients with obesity. Several questions remain regarding the optimal duration and frequency of these exercises to achieve maximum FFM preservation, as well as the specific physiological mechanisms by which mixed training outperforms endurance training in this population.