Effect of high-carbohydrate or high-monounsaturated fatty acid diets on blood pressure: a systematic review and meta-analysis of randomized controlled trials

Abstract

Context: Current dietary guidelines for cardiovascular disease risk management recommend restricting intake of saturated fatty acids (SFAs). However, the optimal macronutrient profile, in the context of a low-SFA diet, remains controversial. The blood-pressure effect of replacing SFAs in diets with monounsaturated fatty acids (MUFAs) compared with carbohydrate has not been quantified to date.

Objective: To synthesize the evidence for the effect of substituting a high-carbohydrate (high-CHO) diet for a high-monounsaturated fatty acid (high-MUFA) diet on blood pressure, a systematic review and meta-analysis of randomized clinical trials in a population without health restrictions was conducted.

Data sources: MEDLINE, EMBASE, and Cochrane Central Register of Controlled Clinical Trials were searched through June 7, 2017. Randomized controlled trials of > 3 weeks duration that assessed the effect of high-MUFA diets in isocaloric substitution for high-CHO diets on systolic blood pressure (SBP) and diastolic blood pressure (DBP) were included.

Data extraction: Data were pooled using the generic-inverse variance method with random effects models and expressed as mean differences (MDs) with 95% confidence intervals (CIs). Heterogeneity was assessed by Cochran Q statistic and quantified by the I2 statistic. The quality of the evidence was assessed with the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system.

Results: Fourteen trials (n = 980 participants) were included in the analysis. Comparatively, the high-MUFA diets in isocaloric substitution for high-CHO diets did not demonstrate a greater reduction in blood pressure (SBP: MD, -0.08 mmHg [95%CI, -1.01 to 0.84], P = 0.86; DBP: MD = 0.01 mmHg [95%CI, -0.73 to 0.75], P = 0.98). The overall quality of the evidence was assessed as moderate.

Conclusions: In the context of low SFAs, high-MUFA diets in isocaloric substitution for high-CHO diets did not affect blood pressure in individuals with and without hypertension. Large-scale trials achieving higher MUFA targets are required to support these findings.

Clinicaltrials.gov id: NCT02626325.

Figures

Figure 1

Flow diagram of the literature search process. The search identified 5829 reports, 4481 of which were determined to be irrelevant based on duplicates and review of titles and abstracts. The remaining 35 reports were reviewed in full. Fourteen randomized controlled trials were included in the analysis. Abbreviations: High-CHO, high-carbohydrate; High-MUFA, high–monounsaturated fatty acids

Figure 2

Forest plot of 14 randomized controlled trials (n = 980 participants) investigating the effect of high–monounsaturated fatty acid and high carbohydrate diets on systolic blood pressure. The pooled effect estimate on systolic blood pressure is represented by the black diamond. Values are mean differences with 95% confidence intervals determined using the generic inverse-variance random-effects model. Interstudy heterogeneity was quantified by I2 at a significance of P < 0.10. n = number of participants in each treatment group. Abbreviations: CI, confidence interval; High-CHO, high-carbohydrate; High-MUFA, high–monounsaturated fatty acid.

Figure 3

Forest plot of 14 randomized controlled trials (n = 980 participants) investigating the effect of high–monounsaturated fatty acid and high-carbohydrate diets on diastolic blood pressure. The pooled effect estimate on diastolic blood pressure is represented by the black diamond. Values are mean differences with 95% confidence intervals determined using the generic inverse-variance random-effects model. Interstudy heterogeneity was quantified by I2 at a significance of P < 0.10. n = number of participants in each treatment group. Abbreviations: CI, confidence interval; High-CHO, high-carbohydrate; High-MUFA, high–monounsaturated fatty acids.

Figure 4

Funnel plots assessing publication bias and effect of small and/or imprecise study effects for systolic blood pressure (A) and diastolic blood pressure (B). The solid line represents the pooled effect estimate expressed as the mean difference for each analysis. The dashed lines represent pseudo 95% confidence intervals. P values are derived from quantitative assessment of publication bias by Egger’s (P = 0.893 for A; P = 0.343 for B) and Begg’s tests (P = 0.256 for A; P = 0.196 for B).