Energy deficiency impairs resistance training gains in lean mass but not strength: A meta-analysis and meta-regression.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of randomized controlled trials
PubMed 34623696 · doi:10.1111/sms.14075
What was done
Systematic review and meta-analysis of randomized controlled trials (searched via PubMed and SportDiscus) investigating resistance training in an energy deficit (RT+ED) lasting at least 3 weeks. Analysis A meta-analyzed trials with a direct parallel non-deficit control group (RT+CON) for lean mass and strength changes. Analysis B matched uncontrolled RT+ED trials to separate RT+CON trials by participant and intervention characteristics. A pooled meta-regression modeled the relationship between the daily caloric deficit magnitude and lean mass changes.
What was found
In parallel controlled trials (Analysis A), RT+ED significantly impaired lean mass gains relative to RT+CON (effect size [ES] = -0.57, p = 0.02), while strength gains were not statistically different (ES = -0.31, p = 0.28). In matched trials (Analysis B), lean mass decreased in RT+ED (ES = -0.11, p = 0.03) versus an increase in RT+CON (ES = 0.20, p < 0.001), while strength improvements were similar (RT+ED ES = 0.84; RT+CON ES = 0.81). Meta-regression revealed that an energy deficit of ~500 kcal/day was the threshold that prevented lean mass gains.
Why it matters
This review establishes that while muscle hypertrophy is blunted and eventually suppressed by moderate energy deficits (~500 kcal/day), strength progression can largely continue during energy restriction.
Limits
The abstract does not state the total number of included studies, participant count, demographics, or training status. Analysis B relies on cross-study matching rather than within-trial randomization, introducing potential confounding. Macronutrient composition (such as daily protein intake) and training volume details were not specified in the abstract.