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

Int J Obes (Lond). 2007 May;31(5):743-50. doi: 10.1038/sj.ijo.0803483. Epub 2006 Oct 31.


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.

Publication types

  • Review
  • Systematic Review

MeSH terms

  • Absorptiometry, Photon
  • Body Composition / physiology*
  • Diet, Reducing*
  • Exercise
  • Female
  • Humans
  • Linear Models
  • Male
  • Obesity* / diet therapy
  • Obesity* / surgery
  • Obesity* / therapy
  • Randomized Controlled Trials as Topic
  • Weight Loss / physiology*