Association of glycaemic index and glycaemic load with type 2 diabetes, cardiovascular disease, cancer, and all-cause mortality: a meta-analysis of mega cohorts of more than 100000 participants

Background: There is debate over whether the glycaemic index of foods relates to chronic disease. We aimed to assess the associations between glycaemic index (GI) and glycaemic load (GL) and type 2 diabetes, cardiovascular disease, diabetes-related cancers, and all-cause mortality. Methods: We did a meta-analysis of large cohorts (≥100 000 participants) identified from the Richard Doll Consortium. We searched the Cochrane Library, MEDLINE, PubMed, Embase, Web of Science, and Scopus for cohorts that prospectively examined associations between GI or GL and chronic disease outcomes published from database inception to Aug 4, 2023. Full-article review and extraction of summary estimates data were conducted by three independent reviewers. Primary outcomes were incident type 2 diabetes, total cardiovascular disease (including mortality), diabetes-related cancers (ie, bladder, breast, colorectal, endometrial, hepatic, pancreatic, and non-Hodgkin lymphoma), and all-cause mortality. We assessed comparisons between the lowest and highest quantiles of GI and GL, adjusting for dietary factors, and pooling their most adjusted relative risk (RR) estimates using a fixed-effects model. We also assessed associations between diets high in fibre and whole grains and the four main outcomes. The study protocol is registered with PROSPERO, CRD42023394689. Findings: From ten prospective large cohorts (six from the USA, one from Europe, two from Asia, and one international), we identified a total of 48 studies reporting associations between GI or GL and the outcomes of interest: 34 (71%) on various cancers, nine (19%) on cardiovascular disease, five (10%) on type 2 diabetes, and three (6%) on all-cause mortality. Consumption of high GI foods was associated with an increased incidence of type 2 diabetes (RR 1·27 [95% CI 1·21–1·34]; p<0·0001), total cardiovascular disease (1·15 [1·11–1·19]; p<0·0001), diabetes-related cancer (1·05 [1·02–1·08]; p=0·0010), and all-cause mortality (1·08 [1·05–1·12]; p<0·0001). Similar associations were seen between high GL and diabetes (RR 1·15 [95% CI 1·09–1·21]; p<0·0001) and total cardiovascular disease (1·15 [1·10–1·20]; p<0·0001). Associations between diets high in fibre and whole grains and the four main outcomes were similar to those for low GI diets. Interpretation: Dietary recommendations to reduce GI and GL could have effects on health outcomes that are similar to outcomes of recommendations to increase intake of fibre and whole grain. Funding: Banting and Best and the Karuna Foundation.