Background: All major guidelines for antihypertensive therapy recommend weight loss. Thus dietary interventions that aim to reduce body weight might be a useful intervention to reduce blood pressure and adverse cardiovascular events associated with hypertension.
Objectives: Primary objectivesTo assess the long-term effects of weight-reducing diets in hypertensive patients on- all cause mortality - cardiovascular morbidity - adverse events (including total serious adverse events, withdrawal due to adverse events and total non-serious adverse events)Secondary objectivesTo assess the long-term effects of weight-reducing diets in hypertensive patients on- change from baseline in systolic blood pressure - change from baseline in diastolic blood pressure - body weight reduction
Search strategy: Studies were obtained from computerised searches of Ovid MEDLINE, EMBASE, CENTRAL and from searches in reference lists and systematic reviews.
Selection criteria: Randomised controlled trials (RCT) in adult hypertensive patients were included if they had a study duration of at least 24 weeks and compared weight reducing dietary interventions to no dietary intervention in adult patients with primary hypertension.
Data collection and analysis: Two authors independently assessed risk of bias and extracted data. Studies were pooled using fixed-effect meta-analysis. In case of moderate or larger heterogeneity as measured by Higgins I(2), a random effects model was used.
Main results: Eight studies involving a total of 2100 participants with high blood pressure and a mean age of 45 to 66 years met our inclusion criteria. Mean treatment duration was 6 to 36 months. No study included mortality as a pre-defined outcome. One RCT evaluated the effects of dietary weight loss on a combined endpoint, consisting of the necessity of reinstating antihypertensive therapy and severe cardiovascular complications. In this RCT weight reducing diet lowered the endpoint, hazard ratio 0.70 (95% confidence interval [CI], 0.57 to 0.87) compared to no diet. None of the studies evaluated adverse events as designated in our protocol. Blood pressure was reduced in patients assigned to weight loss diets as compared to controls: systolic blood pressure (SBP): weighted mean difference (WMD): -4.5 mm Hg; 95% CI, -7.2 to -1.8 mm Hg (3 of 8 studies included in analysis), and diastolic blood pressure (DBP): WMD -3.2 mm Hg; 95% CI, -4.8 to -1.5 mm Hg (3 of 8 studies included in analysis). Patients' body weight was also reduced in dietary weight loss groups as compared to controls, WMD of -4.0 kg (95% CI: -4.8 to -3.2) (5 of 8 studies included in analysis). Two studies used withdrawal of antihypertensive medication as their primary outcome. Even though this was not considered a relevant outcome for this review, the results of these studies strengthen the finding of reduction of blood pressure by dietary weight loss interventions.
Authors' conclusions: In patients with primary hypertension, weight loss diets reduced body weight and blood pressure, however the magnitude of the effects are uncertain as a result of the small number of patients and studies that could be included in the analyses. It is not known whether weight loss reduces mortality and morbidity. No useful information on adverse effects was reported in the relevant trials.