Umbrella Review of Systematic Reviews and Meta-Analyses on Consumption of Different Food Groups and Risk of Type 2 Diabetes Mellitus and Metabolic Syndrome

Type 2 diabetes is a major contributor to the burden of chronic diseases globally. Most cases of type 2 diabetes are preventable through healthy lifestyle modifications in diet and physical activity. This systematic umbrella review presents a comprehensive overview of the evidence about the associations between risk of type 2 diabetes and metabolic syndrome with 13 food groups, including refined and whole grains, fruits, vegetables, nuts, legumes, fish and fish products, eggs, dairy/milk, sugar-sweetened beverages, processed meat, and unprocessed red and white meat. We present these relationships in per-serving and with high-versus-low comparisons. After doing a systematic search in MEDLINE, Embase, Web of Science, and Epistemonikos (registered with PROSPERO: CRD42024547606), we screened 5074 references published until May 15, 2024, and included 67 articles. This included 46 meta-analyses on risk of type 2 diabetes with half a million participants, 17 meta-analyses on risk of metabolic syndrome, and 4 meta-analyses on risk of diabetes-related mortality. Based on quality assessments using AMSTAR-2, 25 of the 67 studies were classified as high-quality studies, 8 as moderate, 12 as low, and 22 as critically low quality. Our results showed that a high intake of whole grains was associated with a lower risk of type 2 diabetes (meta-evidence: moderate) and metabolic syndrome (metaevidence: low), with a similar tendency also for a high intake of fruits and vegetables (metaevidence: moderate). In contrast, the high intakes of processed meat (metaevidence: high), red meat (metaevidence: moderate), and sugar-sweetened beverages (metaevidence: moderate) were associated with a higher risk of type 2 diabetes. For the other food groups, the associations were generally neutral and not statistically significant. The heterogeneity was high for most food groups except fruits, indicating potential differences within each of the food groups in association with type 2 diabetes.