Changes in fat-free mass during significant weight loss: a systematic review.
Level 2 - randomized trial
Systematic review of predominantly non-randomized cohort studies with meta-regression
PubMed 17075583 · doi:10.1038/sj.ijo.0803483
What was done
Medline and Embase were systematically searched for studies with reliable measurements of fat-free mass (FFM) before and after weight loss greater than 10 kg. Data were pooled from 26 dietary and behavioral cohorts and 29 bariatric surgery cohorts. A fixed-effect linear regression model evaluated the proportion of weight lost as FFM (%FFML) against caloric restriction degree, exercise, magnitude of weight loss, initial BMI, and type of surgery.
What was found
Degree of caloric restriction was positively associated with %FFML (r^2 = 0.31, P = 0.006). In three randomized controlled trials, exercise reduced %FFML. Compared with laparoscopic adjustable gastric banding (LAGB), biliopancreatic diversion (BPD) and Roux-en-Y gastric bypass (RYGB) caused greater log-transformed %FFML (r^2 = 0.453, P < 0.001), independent of baseline BMI and total weight lost.
Why it matters
This review demonstrates that aggressive caloric restriction and malabsorptive or bypass bariatric procedures lead to a higher relative loss of lean tissue, whereas adding exercise helps preserve fat-free mass during substantial weight loss.
Limits
The review relies primarily on observational cohort studies rather than randomized surgical trials. Total participant counts, specific body composition measurement modalities, and exact effect sizes for exercise are omitted from the abstract.
Cited by
- context During aggressive caloric restriction or bariatric surgery without resistance training or high protein intake, approximately 40% of the weight lost is muscle.