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> 10 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.