The green plate effect: Systematic review and meta-analyses of vegan diets and metabolic health in adults- findings from randomized controlled trials

The increasing global interest in consuming plant-based diets, especially the vegan diet, is fuelled by ethical, health, and environmental concerns. A balanced and diverse vegan diet has the potential to play a significant role in achieving and sustaining optimal health, particularly in diet-based interventions for metabolic syndrome. This systematic review evaluated randomised controlled trials, to elucidate the effects of a strict vegan diet on individual components of metabolic syndrome in the human population. A comprehensive literature search was conducted across four databases (Cochrane Central Register of Controlled Trials; Embase via Ovid; Ovid Medline; Scopus). The search covered articles published between 2013 and 2024, specifically targeting MeSH terms associated with “vegan” and “metabolic syndrome.”. Data extraction and quality assessment were independently carried out by two reviewers. Out of the 4094 identified publications, 18 articles were included, detailing 11 distinct trials. Subgroup analysis revealed that vegan diets significantly reduced body weight (−10.37 kg; 95 % CI: [7.07, 13.67]; p < 0.00001), BMI (−2.68 kg/m 2 ; 95 % CI: [1.87, 3.85]; p < 0.00001), LDL-c (−0.44; 95 % CI: [0.40, 0.48]; p = 0.0001), total cholesterol (−0.42 mmol/L; 95 %CI: [-0.73, −0.12]; p = 0.007), and HbA1c (−0.17 %; 95 % CI: [0.01, 0.32]; p = 0.04) with the most pronounced effects seen in individuals with metabolic syndrome and type 2 diabetes mellitus. These improvements are likely mediated by enhanced satiety, reduced saturated fat intake, improved insulin sensitivity, and gut microbiota modulation. However, no consistent effects were observed in triglycerides, HDL-c, or blood pressure, and substantial heterogeneity was noted across some outcomes. Overall, vegan diets demonstrate promising potential as a sustainable, non-pharmacological strategy for managing cardiometabolic risk, particularly in individuals with existing metabolic dysfunction. • Vegan diets, rich in fibre and plant-based compounds, have the potential in improving metabolic health. • Vegan diets significantly reduced metabolic parameters, in metabolic syndrome and type 2 diabetes mellitus. • Greater improvements in those with impaired insulin sensitivity, suggesting greater responsiveness among the metabolically compromised. • No major changes were in triglycerides, HDL-c or blood pressure, with notably high heterogeneity across these outcomes. • These findings support the importance of a vegan diet as a practical and sustainable options for metabolic health. Prospero 2022 Registration no. CRD42022359624; Available at: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022359624 .