Background: Dietary fiber has played a consistent role in weight management, with efficacy potentially attributed to increased viscous fiber consumption. Purpose: To summarize the effects of viscous fiber on body weight and other anthropometric parameters, along with a calorie-deficient diet, through a systematic review and meta-analysis. Methods: MEDLINE, EMBASE, and the Cochrane library were searched through July 24, 2019 for randomized controlled trials that assessed the effect of viscous fiber supplementation as part of a restricted calorie diet for ≥ 4 weeks relative to comparator diets. Data were pooled using the generic inverse-variance method with random-effects models and expressed as mean differences with 95% confidence intervals. Inter-study heterogeneity was assessed using Cochran’s Q and quantified with I2. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was used to evaluate the overall certainty of evidence. Results: Findings from 15 studies (n = 1347) showed viscous fiber supplementation significantly decreased body weight (− 0.81 kg [− 1.20, − 0.41]; p < 0.0001), BMI (− 0.25 kg/m2 [− 0.46, − 0.05]; p = 0.01), and body fat (− 1.39% [− 2.61, − 0.17]; p = 0.03), compared to control. No effect on waist circumference was found. The certainty of evidence was graded as “moderate” for body weight, BMI, and body fat based on downgrades for imprecision. Waist circumference was graded “low” for downgrades of inconsistency and imprecision. Conclusion: Viscous fiber within a calorie-restricted diet significantly improved body weight and other markers of adiposity in overweight adults and those with additional risk factors for cardiovascular disease. This trial is registered at www.clinicaltrials.gov as NCT03257449. Registration: ClinicalTrials.gov identifier: NCT03257449.