The quality of evidence is downgraded by study limitations (unclear allocation concealment and blinding), by indirectness (differences between the outcomes of interest and those reported: only short-term and surrogate outcomes reported), and by by imprecise results (few patients and wide confidence intervals).
A Cochrane review [Abstract] 1 included 21 studies with a total of 2 538 subjects, examining the effect of low glycaemic index (GI) diets or foods compared with higher GI diets or foods on risk factors for cardiovascular disease over 12 weeks or more. Twenty studies were in a primary prevention population and 1 in a secondary prevention population. Most of the studies did not have an intervention duration of longer than 6 months. Difference in GI between comparison groups varied widely from 0.6 to 42.
None of the studies reported on mortality or cardiovascular events. Overall, in the primary prevention studies, no evidence of a difference between low GI and high GI groups was seen for blood lipid parameters and blood pressure parameters: total cholesterol (MD -0.12 mmol/L, 95% CI -0.26 to 0.02), HDL cholesterol (MD -0.00 mmol/L, 95% CI -0.03 to 0.02), LDL cholesterol (MD -0.03 mmol/L, 95% CI -0.10 to 0.04), triglycerides (MD 0.03 mmol/L, 95% CI -0.03 to 0.09), systolic blood pressure (MD 0.52 mmHg, 95% CI -1.21 to 2.25), and diastolic blood pressure (MD -0.23 mmHg, 95% CI -1.42 to 0.96). In the secondary prevention study, no evidence of any differences were observed between low and high GI groups on any reported outcomes of this review. Only 2 of the included studies (n=38) reported on adverse effects and did not observe any harms.
Primary/Secondary Keywords