Results of this randomized controlled trial demonstrate that the DASH diet produces significant reductions in BP compared with a typical American diet among unmedicated, overweight or obese men and women with high BP and that weight loss and exercise combined with the DASH diet produce additional BP lowering. Compared with UC, we observed a 12.5/5.9 mm Hg net benefit in clinic-measured BP with the DASH-WM program consisting of aerobic exercise, caloric restriction, and cognitive-behavioral intervention and a 7.7/3.6 mm Hg net benefit with DASH-A. These findings confirm the value of the DASH diet in reducing BP and provide evidence for the significant “added value” associated with exercise and weight loss in the context of the DASH diet.
The efficacy of the DASH diet initially was established on the basis of several controlled feeding trials designed to examine the effects of dietary patterns on BP among unmedicated persons with higher-than-optimal DBP or with stage 1 hypertension; as a result of these studies, the DASH diet was adopted as part of current national recommendations for the prevention and treatment of high BP.1
The subsequent PREMIER study6
demonstrated the feasibility of implementing the DASH diet in daily life, but the small and nonsignificant BP differences between the DASH diet and the “established” intervention (which also involved some dietary changes) raised doubts about the added value of the DASH diet in optimizing BP. Because participants in the DASH plus “established” intervention lost more weight than the “established” intervention alone, the effects of the DASH diet could not be determined. The ENCORE trial has now extended the PREMIER study by not only examining the extent to which lifestyle modifications can be adopted in the home environment but also by manipulating the DASH diet intervention and weight loss independently. Our results confirm the findings of the earlier DASH feeding studies: participants who ate the DASH diet achieved significant BP reductions.3–5
However, adding exercise and weight loss led to an even greater decrease in BP.
The BP reductions achieved in our DASH-A and DASH-WM interventions were greater than those described in the PREMIER study and in other trials of lifestyle modification.22–24
The reasons for the greater benefit from the current ENCORE intervention could be attributed to the greater weight loss and excellent adherence to the DASH diet and exercise sessions. The 12/6 mm Hg relative reduction in BP that we observed among participants randomized to DASH-WM is equivalent to the BP lowering that physicians could expect from a high dose of an antihypertensive drug.25
Similar BP reductions have been achieved in placebo-controlled treatment trials and have resulted in a lowering of stroke risk by approximately 40% and a reduction in ischemic heart disease events by about 25%.26
In addition to BP lowering, we demonstrated improvements in important cardiovascular biomarkers. One of the structural consequences of high BP, left ventricular hypertrophy (LVH), is the strongest known predictor, other than advancing age, of cardiovascular morbidity and mortality. Increased LV mass predicts these clinical outcomes in hypertensive27
and healthy individuals,28
independent of other conventional risk factors. Drug therapy that results in LVH regression29
is associated with improved cardiovascular outcomes. For example, Verdecchia et al30
found a lower risk of cardiovascular events in hypertensive participants who had a decrease in LV mass during treatment, independent of baseline BP or the degree of BP reduction. Similarly, in a substudy of the Losartan Intervention of Endpoint Reduction in Hypertension (LIFE) trial, lowered LV mass was associated with decreased rates of cardiovascular events.31
Arterial stiffness also has been shown to be a strong independent predictor of cardiovascular morbidity and mortality.32–35
The DASH-A and the DASH-WM interventions resulted in greater reductions in PWV than did UC, with more pronounced reductions among the DASH-WM participants. Dietary sodium intake was reduced by approximately 30% compared with UC, and participants in the DASH-WM group achieved a 19% improvement in aerobic capacity, which may have augmented the benefits of the DASH diet and weight loss on arterial stiffness. The observed reductions in PWV may be a result of the direct impact of diet and exercise as well as the lower BP resulting from these lifestyle changes. A reduction in arterial stiffness may also contribute to regression of LVH. The Ohasama study showed that arterial stiffness measured by PWV was related to LVH, independent of age and BP, in a population of 798 older adults.36
Ongoing trials should help clarify whether reducing arterial stiffness contributes to a lowered risk for cardiovascular events.37
Impairment of the sensitivity of the baroreflex system is an early consequence of hypertension38– 41
and likely reflects reduced viscoelastic properties of the vascular wall housing the baroafferent stretch receptors owing to arterial stiffness and atherosclerosis.42– 44
The DASH-A intervention did not alter BRS, but DASH-WM improved BRS by 33%. The improvements in BRS may result from reduced vascular stiffness45– 47
or improved parasympathetic cardiac control through improved insulin sensitivity and glucose metabolism secondary to exercise and weight loss.48
The present study is limited by its relatively small sample of highly motivated participants along with a labor-intensive treatment program that may be difficult to fully implement in clinical practice. The ENCORE study was not powered to detect differences in “hard” clinical end points, such as stroke, myocardial infarction, and death. Trials of pharmacologic therapy, however, demonstrate that BP lowering reduces the risk of cardiovascular events and that the magnitude of BP reduction and reversal of cardiovascular structural changes associated with hypertension are key determinants of the effectiveness of therapy.49
Ultimately, the effects of the DASH diet and weight management will need to be evaluated prospectively in a larger sample of participants; longer-term follow-up of ENCORE study participants is currently ongoing. The present findings suggest that the DASH diet, particularly when augmented by exercise and weight loss, can offer considerable benefit to patients with high BP, not only through reductions in BP but through favorable modification of biomarkers of disease risk.