Compared to the general population, patients with high blood pressure have a higher risk for death and complications such as heart attack or stroke. Based on the association of increased weight and increased blood pressure, dietary interventions to lower body weight are commonly recommended as a first therapeutic step for overweight patients with high blood pressure. However, whether weight loss has a long-term effect on blood pressure and reduces the adverse effects of elevated blood pressure remains unclear. As only randomised controlled trials (RCT) comparing groups with and without a weight reducing diet can answer these issues, we only included RCTs in our systematic review. 30 articles reporting on eight studies met the inclusion criteria. The 8 included studies involved a total of 2100 participants with high blood pressure and a mean age of 45 to 66 years. Mean treatment duration was 6 to 36 months and there was little or no information about deaths or other long-term complications. In three of eight studies, effects on systolic and diastolic blood pressure were provided, showing that systolic and diastolic blood pressure were reduced by weight loss interventions by 4.5 mm Hg and 3.2 mm Hg, respectively. Five out of eight studies reported body weight, and weight loss interventions reduced weight by 4.0 kg as compared to controls. No useful information on possible adverse effects was reported in the included trials.
In conclusion, there is no evidence for effects of weight loss diets on death or long-term complications and adverse events. In addition, results on blood pressure and body weight could be considered uncertain, because not all studies were included in the analyses. But these results are mainly based on one large study with about 600 participants that was judged to be of high quality, and the fact that most of the other studies excluded from analysis indirectly (e.g. via successful withdrawal of blood pressure reducing drugs) further underline these effects, gives confidence in the obtained results. —Cochrane 2011