Association of weight status and the risks of diabetes in adults: a systematic review and meta-analysis of prospective cohort studies

Obesity is a known risk factor for type 2 diabetes mellitus (T2DM); however, the associations between underweight and T2DM and between weight status and prediabetes have not been systematically reviewed. We aimed to estimate the relative risks (RRs) of prediabetes/T2DM in underweight/overweight/obesity relative to normal weight. PubMed, Embase, Web of Science, and Cochrane Library were searched from inception to December 8, 2021. Prospective cohort studies with a minimum 12-month follow-up period reporting the association between baseline body mass index (BMI) categories and risk of prediabetes/T2DM in adults were included. Study quality was assessed using the Newcastle-Ottawa Scale. The main analyses of T2DM risk were performed using the ethnic-specific (Asian/non-Asian) BMI classification and additional analyses of prediabetes/T2DM risk by including all eligible studies. Random-effects models with inverse variance weighting were used. Subgroup analyses and meta-regression were conducted to explore the potential effects of pre-specified modifiers. The study protocol was registered with PROSPERO (CRD42020215957). Eighty-four articles involving over 2.69 million participants from 20 countries were included. The pooled RR of prediabetes risk was 1.24 (95% CI: 1.19-1.28, I