Preservation of fat-free mass in the first year after bariatric surgery: a systematic review and meta-analysis of 122 studies and 10,758 participants

The main goal of bariatric surgery (BS) in patients with morbid obesity is reducing body mass and fat mass (FM). However, body mass loss is systematically accompanied by a decline in fat-free mass (FFM). We aimed to examine the time-course effect of BS on FFM and body FFM percentage (FFM%) in individuals with morbid obesity by conducting a systematic review and meta-analysis of controlled adult human trials. We searched PubMed, Scopus, Embase, Institute for Scientific Information Web of Science, and Cochrane databases within the period from October 2002 to May 2021, with no restriction in the English language, to find studies assessing the effect of BS on FFM and FFM% in patients with morbid obesity. A meta-analysis of 122 studies carried out on data of 10,758 patients with morbid obesity after BS showed that BS was associated with a substantial decrease in FFM at 1 (–3.47 kg [95% confidence interval [CI]: –3.88, –3.07]), 3 (–5.59 kg [95% CI: –6.01, –5.17], 6 (–6.61 kg [95% CI: –7.25, –5.98]), and 12 (–8.34 kg [95% CI: –9.04, –7.63]) months after the surgery; however, the FFM% increased at 3 (6.51% [95% CI: 5.00, 8.02]), 6 (8.56% [95% CI: 6.81, 10.31], and 12 (11.29% [95% CI: 8.94, 13.64]) months after the surgery. BS was associated with sustained declines in FFM and increases in FFM% from 1–12 months with no indication of plateau phase postoperatively. These findings emphasize that postbariatric care should focus more on FFM loss during the first year after surgery. •The bariatric surgeries induces a long-lasting body mass and/or fat loss; thus, there is some concern about decreasing lean mass.•The quantitative impact of the body mass loss following BS on FFM changes and its trend within one year after surgery is unsettled yet.•BS was associated with a substantial decrease in -3.47 kg, -5.59 kg, -6.61 kg and -8.34 kg FFM at 1 , 3 , 6 and 12 months after the surgery.•BS was associated with substantial increase in 6.51%, 8.56% and 11.29% FFM% at 3, 6, and 12 months after the surgery.