Glycemic index, glycemic load, and blood pressure: a systematic review and meta-analysis of randomized controlled trials

Background: High blood pressure is a strong risk factor for cardiovascular disease. Objectives: The aim was to determine the associations of dietary glycemic index (GI) and glycemic load (GL) with systolic blood pressure (SBP) and diastolic blood pressure (DBP) in healthy individuals. Design: A systematic review and meta-analysis of randomized controlled trials (RCTs) was carried out. Databases were searched for eligible RCTs in two phases. Medline, Embase, CAB Abstracts, BIOSIS, ISI Web of Science and the Cochrane Library were searched from January 1990 to December 2009. An updated search was undertaken using Medline and Embase from January 2010 to September 2016. Trials were included if they reported author-defined high and low GI or GL diets and blood pressure, were of at least 6 weeks duration, and comprised healthy participants without chronic conditions. Data were extracted and analyzed using STATA statistical software. Pooled estimates and 95% confidence intervals (CI) were calculated using weighted mean differences and random effects models. Results: Data were extracted from 14 trials comprising 1097 participants. Thirteen trials provided information on differences in GI between control and intervention arms. A median reduction in GI of 10 units, reduced the overall pooled estimates for SBP and DBP by 1.1mmHg (95% CI, -0.3 to 2.5, p=0.11) and 1.3 mmHg (95% CI 0.2 to 2.3, p=0.02) respectively. Nine trials reported information on differences in GL between arms. A median reduction in GL of 28 units reduced the overall pooled estimates for SBP and DBP by 2.0 mmHg (95% CI, 0.2 to 3.8, p=0.03) and 1.4 mmHg (95% CI, 0.1 to 2.6, p=0.03) respectively. Conclusion: This review of healthy individuals, indicated that a lower glycemic diet may lead to important reductions in blood pressure. However, many of the trials included in the analysis reported important sources of bias.