Health Effects of Plant-Based Diets in People with Overweight or Obesity: A Systematic Review and Meta-Analysis

Background/Objectives: Nutrition plays a core role in chronic disease management, and there is growing interest in the health impact of plant-based diets (PBDs) in people with overweight or obesity. We conducted this systematic review and meta-analysis to summarize the evidence on the health effect of PBDs compared to omnivorous diets in overweight or obese individuals. Methods: We searched the databases Cochrane Central Register of Controlled Trials, MEDLINE, Embase, ClinicalTrials.gov and WHO International Clinical Trials Registry Platform from inception to 3 January 2024. Two review authors independently screened studies for eligibility, extracted data, evaluated the risk of bias, and rated the certainty of the evidence using GRADE. This study is registered with PROSPERO, CRD42021225525. We used random-effects meta-analysis to analyze data. Results: Of 2664 records identified, 10 randomized controlled trials (RCTs) and six ongoing studies met the inclusion criteria. The available evidence suggests little to no difference between plant-based and omnivorous diets for body weight, systolic blood pressure, diastolic blood pressure, serum glucose, serum insulin, insulin sensitivity, total cholesterol, triglyceride, HDL cholesterol and body fat mass. Plant-based diets may slightly reduce LDL cholesterol. They may also reduce BMI and HbA1c, although the certainty of the evidence is very low. Longer-duration dietary interventions (14 weeks or more) showed greater improvements in BMI, LDL cholesterol and HbA1c. Conclusions: Plant-based diets may represent a dietary option for people with overweight or obesity and may support modest improvements in selected cardiometabolic outcomes, although the available evidence is limited and uncertain. Most outcomes showed little or no difference between PBDs and comparison diets, while the observed effects on BMI and HbA1c were supported by very low certainty evidence.