Whole-grain and blood lipid changes in apparently healthy adults: a systematic review and meta-analysis of randomized controlled studies

Background: Whole grains are recognized for their potential role in preventing cardiovascular diseases; however, results from randomized controlled studies on blood lipids are inconsistent, potentially because of compositional differences between individual grain types for some nutrients, including dietary fiber. Objective: Using a meta-analytic approach, we assessed the effect of whole-grain compared with non-whole-grain foods on changes in total cholesterol (TC), LDL cholesterol, HDL cholesterol, and triglycerides. Design: We conducted a systematic literature search in selected databases. Studies were included if they were randomized controlled comparisons between whole-grain foods and a non-whole-grain control in adults. A total of 6069 articles were screened for eligibility, and data were extracted from 24 studies. Weighted mean differences were calculated, and meta-regression analyses were performed for whole-grain dose, study duration, and baseline TC concentration. Results: Overall, whole-grain intake lowered LDL cholesterol (weighted difference: 20.09 mmol/L; 95% CI: 20.15, 20.03 mmol/L; P < 0.01) and TC (weighted difference: 20.12 mmol/L; 95% CI: 20.19, 20.05 mmol/L; P < 0.001) compared with the control. Whole-grain oat had the greatest effect on TC (weighted difference: 20.17 mmol/L; 95% CI: 20.10, 20.25 mmol/L; P < 0.001). No effect of whole-grain foods on HDL cholesterol was seen, whereas whole-grain foods tended to lower triglycerides compared with the control (weighted difference: 20.04 mmol/L; 95% CI: 20.08, 0.01; P = 0.10). No association was found between whole-grain dose or baseline TC concentration and any of the outcomes, whereas study duration was positively associated with changes in TC and LDL cholesterol. Conclusions: Consumption of whole-grain diets lowers LDL cholesterol and TC, but not HDL cholesterol or triglycerides, compared with consumption of non-whole-grain control diets. Whole-grain oat appears to be the most effective whole grain for lowering cholesterol.