Changes in fat-free mass during significant weight loss: a systematic review

Objective: To identify the proportion of weight lost as fat-free mass (FFM) by various weight loss interventions. Methods: Medline and Embase were systematically searched for reliable measurements of FFM before and after weight loss of 410 kg and eligible data were pooled. In a fixed effect model of % FFM loss/weight loss (% FFML), linear regression analysis was used to determine the influence of degree of caloric restriction, exercise, magnitude of weight loss, initial body mass index (BMI) and type of surgery. Results: Data were included from 26 cohorts treated with dietary and behavioral interventions and 29 cohorts of bariatric surgery patients. The degree of caloric restriction was positively associated with % FFML (r(2) = 0.31, P = 0.006) and in three randomized controlled trials exercise was shown to decrease % FFML. Compared with laparoscopic adjustable gastric banding (LAGB), biliopancreatic diversion (BPD) and roux en Y gastric bypass (RYGB) caused greater log(e) (natural log) % FFML (r(2) = 0.453, P < 0.001). Differences in log(e) % FFML between surgical procedures were independent of initial BMI and magnitude of weight loss. Conclusions: The degree of caloric restriction, exercise and rate of weight loss influence the proportion of weight lost as FFM after non-surgical interventions. For surgical interventions, BPD and RYGB result in greater % FFML than LAGB.