Carbohydrates, glycemic index, glycemic load, and colorectal cancer risk: a systematic review and meta-analysis of cohort studies

Background Dietary carbohydrate, glycemic index, and glycemic load are thought to influence colorectal cancer risk through hyperinsulinemia. We review and quantitatively summarize in a meta-analysis the evidence from prospective cohort studies. Methods We searched the PubMed database for prospective studies of carbohydrate, glycemic index, and glycemic load and colorectal cancer risk, up to October 2011. Summary relative risks were estimated by the use of a random effects model. Results We identified 14 cohort studies that could be included in the meta-analysis of carbohydrate, glycemic index, and glycemic load and colorectal cancer risk. The summary RR for high versus low intake was 1.00 (95% CI: 0.87-1.14, I-2 = 31%) for carbohydrate, 1.07 (95% CI: 0.99-1.16, I-2 = 28%) for glycemic index, and 1.00 (95% CI: 0.91-1.10, I-2 = 39%) for glycemic load. In the dose-response analysis, the summary RR was 0.95 (95% CI: 0.84-1.07, I-2 = 58%) per 100 grams of carbohydrate per day, 1.07 (95% CI: 0.99-1.15, I-2 = 39%) per 10 glycemic index units, and 1.01 (95% CI: 0.95-1.08, I-2 = 47%) per 50 glycemic load units. Exclusion of one or two outlying studies reduced the heterogeneity, but the results were similar. Conclusion This meta-analysis of cohort studies does not support an independent association between diets high in carbohydrate, glycemic index, or glycemic load and colorectal cancer risk.