The role of dietary fiber in obesity management remains debatable. Evidence suggests that intake of viscous fiber may have the potential to facilitate weight loss.We aimed to summarize and quantify the effects of viscous fiber on body weight, BMI, waist circumference, and body fat, independent of calorie restriction, through a systematic review and meta-analysis of randomized controlled trials.Trials ≥4 wk in duration that assessed the effect of viscous fiber supplemented to an ad libitum diet along with comparator diets were included. MEDLINE, EMBASE, and the Cochrane library were searched through 24 July, 2019. Two independent reviewers extracted relevant data. Data were pooled using the generic inverse variance method and random-effects models and expressed as mean differences with 95% CIs. Interstudy heterogeneity was assessed (Cochran Q statistic) and quantified (I2 statistic). The overall certainty of evidence was explored using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach.Findings from 62 trials (n = 3877) showed that viscous fiber reduced mean body weight (-0.33 kg; 95% CI: -0.51, -0.14 kg; P = 0.004), BMI (in kg/m2) (-0.28; 95% CI: -0.42, -0.14; P = 0.0001), and waist circumference (-0.63 cm; 95% CI: -1.11, -0.16 cm; P = 0.008), with no change in body fat (-0.78%; 95% CI: -1.56%, 0.00%; P = 0.05) when consumed with an ad libitum diet. Greater reductions in body weight were observed in overweight individuals and those with diabetes and metabolic syndrome. The certainty of evidence was graded moderate for body weight, high for waist circumference and body fat, and low for BMI.Dietary viscous fiber modestly yet significantly improved body weight and other parameters of adiposity independently of calorie restriction. Future trials are warranted to address the inconsistency and imprecision identified through GRADE and to determine long-term weight-loss sustainability.This systematic review and meta-analysis was registered at clinicaltrials.gov as NCT03257449.