Glycemic index, glycemic load, and blood pressure: a systematic review and meta-analysis of randomized controlled trials
The associations of dietary glycemic index (GI) and glycemic load (GL) with systolic blood pressure (SBP) and diastolic blood pressure (DBP) in healthy individuals.
High blood pressure is a strong risk factor for cardiovascular disease. The aim of this study was to determine the associations of glycemic index (GI) and glycemic load (GL) with systolic blood pressure (SBP) and diastolic blood pressure (DBP) in healthy individuals. A systematic review and meta-analysis of randomized controlled trials (RCTs) was carried out. Databases were searched for eligible RCTs in 2 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 with the use of 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 $6 wk duration, and comprised healthy participants without chronic conditions. Data were extracted and analyzed with the use of Stata statistical software. Pooled estimates and 95% CIs were calculated with the use of weighted mean differences and random-effects models. 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 1.1 mm Hg (95% CI: 20.3, 2.5 mm Hg; P = 0.11) and 1.3 mm Hg (95% CI: 0.2 mm Hg, 2.3; P = 0.02), respectively. Nine trials information on differences in GL between arms. A median in GL of 28 units reduced the overall pooled estimates for SBP and DBP by 2.0 mm Hg (95% CI: 0.2, 3.8 mm Hg; P = 0.03) and 1.4 mm Hg (95% CI: 0.1, 2.6 mm Hg; P = 0.03), respectively. 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 important sources of bias.
In relatively healthy individuals, lower-glycemic diets are associated with significantly better profiles of blood pressure, although no clear dose response was apparent in these analyses. Furthermore, many of the trials included in the review aimed to reduce weight in participants, making it difficult to isolate the impact of diet on blood pressure. The trials were also subject to considerable sources of bias, as is often the case in trials involving food-based interventions. Before lower-glycemic diets are universally recommended by health professionals, high-quality trials in healthy normal-weight populations are needed to determine the effects of GI on blood pressure independent of weight change.