Animal studies have shown the beneficial effect of betaine supplementation on reducing body fat, while the data from human studies are controversial and inconsistent. The objective of the present systematic review was to investigate the effects of betaine intervention on treating obesity in humans and quantitatively evaluate the pooled effects based on randomized controlled trials with a meta-analysis. The PubMed and Scopus databases, and the Cochrane Library, were searched up to September 2019. Weighted mean differences were calculated for net changes in obesity-related indices by using a random-effects model. Publication bias was estimated using Begg’s test. Six studies with 195 participants were identified. Betaine supplementation significantly reduced the total body fat mass (−2.53 kg; 95% CI: −3.93, −0.54 kg; I2
= 6.6%, P = 0.36) and body fat percentage (−2.44%; 95% CI: −4.20, −0.68%; I2
= 0.0%, P = 0.44). No changes were observed regarding body weight (−0.29 kg; 95% CI: −1.48, 0.89 kg; I2
= 0.00%, P = 0.99) and body mass index (−0.10 kg/m2
; 95% CI: −5.13, 0.31 kg/m2
= 0.00%, P = 0.84). The results suggested that dietary betaine supplementation might be an effective approach for reducing body fat.
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