The role of dietary diversity in preventing metabolic-related outcomes: Findings from a systematic review.

Dietary diversity has been linked to insulin resistance; however, studies are inconsistent on whether dietary diversity protects against metabolic-related outcomes. We aimed to comprehensively assess metabolic-related outcomes of greater diversity across the diet and within major food groups. A systematic search of peer-reviewed literature was done in bibliographic databases (Medline, Scopus, and Web of Science) for longitudinal studies that reported on original research. Data extraction and quality appraisal used predefined criteria; reported findings were synthesized through a narrative approach. Fourteen studies were identified as eligible. Greater dietary diversity across major food groups, and diversity within fruits and/or vegetables, was associated with reduced risk of type 2 diabetes (T2D). Effects varied based on exposure definition and adjustment for known confounders. While diversity of less healthy foods was associated with greater adiposity, diversity of all foods and healthy foods was associated with reduced incidence of depression and cognitive decline. Evidence supports the protective effect of dietary diversity against cognitive decline and T2D. The association between dietary diversity and adiposity may be dependent on the healthiness of foods. Public health efforts to prevent metabolic-related diseases should include an emphasis on a varied diet as a healthy eating strategy.