The New England Journal of Medicine APRIL 17, 1997

A Clinical Trial of the Effects of Dietary Patterns on Blood Pressure

Appel LJ, Moore TJ, Obarzanek E, et al. (DASH Collaborative Research Group)

Bottom Line

The DASH trial demonstrated that a dietary pattern rich in fruits, vegetables, and low-fat dairy products, with reduced saturated fat and total fat, significantly lowers blood pressure in adults compared to a typical American diet.

Key Findings

1. The DASH (combination) diet reduced systolic blood pressure by 5.5 mm Hg and diastolic blood pressure by 3.0 mm Hg more than the control diet (P<0.001 for both).

2. A diet rich only in fruits and vegetables reduced systolic blood pressure by 2.8 mm Hg (P<0.001) and diastolic blood pressure by 1.1 mm Hg (P=0.07) more than the control diet.

3. In the subset of 133 hypertensive participants, the DASH diet produced a greater net reduction of 11.4 mm Hg systolic and 5.5 mm Hg diastolic blood pressure compared to the control diet.

4. The blood pressure-lowering effects were observed within two weeks of starting the intervention and were consistent across various demographic subgroups, including race and gender.

Study Design

Design

RCT

N/A

Sample

459

Patients

Duration

8 wk

Median

Setting

Multicenter, US

Population Adults aged 22 years and older with systolic blood pressure less than 160 mm Hg and diastolic blood pressure between 80 and 95 mm Hg.

Intervention A diet rich in fruits, vegetables, and low-fat dairy products, and reduced in saturated fat, total fat, and cholesterol.

Comparator A typical American diet, low in fruits, vegetables, and dairy products, with a fat and nutrient profile reflective of average U.S. consumption.

Outcome Change in diastolic blood pressure from baseline to the end of the 8-week intervention.

Study Limitations

• The study was a highly controlled feeding trial, which may not reflect the adherence challenges of real-world, free-living populations making their own food choices.

• The duration of the intervention was short (8 weeks), providing no data on the long-term sustainability or durability of these blood pressure reductions.

• The study was not designed to assess clinical cardiovascular outcomes, such as rates of myocardial infarction or stroke, only surrogate markers (blood pressure).

• The strict provision of all food by researchers limits the generalizability regarding the feasibility of adopting this diet in standard community settings without significant support.

Clinical Significance

The DASH diet serves as a fundamental, evidence-based nonpharmacological intervention for the prevention and treatment of hypertension. Its efficacy provides a robust nutritional strategy that can be recommended alongside or instead of medication for patients with prehypertension or stage 1 hypertension, reducing the need for or dosage of antihypertensive drugs.

Historical Context

Prior to this trial, dietary guidelines for hypertension focused primarily on sodium restriction, alcohol moderation, and weight loss. While observational studies had suggested links between various nutrients (potassium, calcium, magnesium) and blood pressure, previous clinical trials of single-nutrient supplementation had yielded inconsistent results. The DASH trial shifted the paradigm by testing whole dietary patterns, establishing a reproducible, effective lifestyle approach that has since been adopted by major health organizations globally.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

What are the primary physiological mechanisms by which the increased intake of potassium, magnesium, and calcium in the DASH dietary pattern contributes to a reduction in systemic vascular resistance?

Key Response

The DASH diet is rich in these cations. Potassium promotes vasodilation by activating sodium-potassium pumps and opening potassium channels in vascular smooth muscle, while also facilitating natriuresis. Magnesium acts as a natural calcium channel antagonist, and adequate calcium intake is thought to suppress parathyroid hormone and 1,25-dihydroxyvitamin D, thereby reducing intracellular calcium in vascular cells and lowering tone.

Resident

In a patient with Stage 1 hypertension and a 10-year ASCVD risk of less than 10%, how does the magnitude of systolic blood pressure reduction observed in the DASH trial compare to standard pharmacological monotherapy?

Key Response

The DASH trial demonstrated a mean systolic reduction of 5.5 mmHg in the overall cohort and a more robust 11.4 mmHg reduction in participants with hypertension. This efficacy is comparable to the 5–10 mmHg reduction typically achieved with a single first-line antihypertensive agent (e.g., ACE inhibitor or thiazide), justifying the use of DASH as a primary management strategy before initiating medication in low-risk patients.

Fellow

The original DASH trial held sodium intake constant at approximately 3,000 mg/day across all groups. How should a clinician reconcile these findings with the later DASH-Sodium trial when managing patients with salt-sensitive hypertension or early-stage Chronic Kidney Disease?

Key Response

The original DASH trial proved that a dietary pattern high in fruits, vegetables, and low-fat dairy reduces BP independently of sodium restriction. However, the subsequent DASH-Sodium trial showed an additive effect, where combining the DASH pattern with low sodium (1,500 mg) produced the greatest BP lowering. For salt-sensitive or CKD patients, the synergy between the DASH micronutrient profile and sodium restriction is critical for optimizing volume status and vascular compliance.

Attending

Despite the 'gold-standard' status of the DASH trial, what are the primary systemic barriers to its implementation in clinical practice, and how can we transition from merely advising a diet to ensuring its delivery as a therapeutic intervention?

Key Response

The DASH trial was a controlled feeding study where food was provided; real-world implementation is hindered by food deserts, the high cost of fresh produce, and the time required for meal preparation. Attending-level insight involves advocating for 'food as medicine' programs, referral to registered dietitians, and addressing social determinants of health to bridge the gap between clinical efficacy and community effectiveness.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

Evaluate the trade-offs between the 'controlled feeding' methodology used in DASH and a 'pragmatic' dietary trial design. How does the high internal validity of the DASH study limit our understanding of the behavioral and psychological mediators of dietary adherence?

Key Response

By providing all meals, DASH ensured nearly 100% compliance with the nutrient targets, isolating the biological effect of the diet. However, this ignores the complex behavioral chain of food selection, purchasing, and preparation. Building on this research requires 'implementation science' studies that test the efficacy of the DASH pattern when delivered through nutritional education versus direct provision in diverse, non-clinical environments.

Journal Editor

As a reviewer, how would you critique the choice of the 'control diet' (a typical American diet low in minerals and fiber) regarding its potential to inflate the perceived effect size of the DASH intervention?

Key Response

A critical reviewer would flag that the control diet was designed to be low in the very nutrients (potassium, magnesium, calcium) the intervention aimed to increase, potentially creating a 'best-case scenario' for the intervention. While this establishes a clear biological contrast, it may overstate the benefit compared to a control group simply following general healthy eating guidelines (e.g., the USDA Food Pyramid).

Guideline Committee

Given that the DASH trial provided Level 1a evidence for blood pressure reduction, how do current ACC/AHA and ESC/ESH guidelines weight this dietary pattern compared to other lifestyle modifications like aerobic exercise or weight loss?

Key Response

Current ACC/AHA guidelines (2017) and ESC/ESH guidelines (2023) grant the DASH diet a Class I, Level A recommendation. The DASH diet's 11 mmHg SBP reduction in hypertensives is often cited as the most potent non-pharmacological intervention, surpassing the average effects of weight loss (approx. 1 mmHg per kg) or aerobic exercise (approx. 5-8 mmHg), though guidelines emphasize a multi-modal approach combining all three for maximum risk reduction.

Clinical Landscape

Noteworthy Related Trials

1997

TOHP II

n = 2,382 · JAMA

Tested

Weight loss and sodium reduction interventions

Population

Overweight adults with high-normal blood pressure

Comparator

Usual care

Endpoint

Incidence of hypertension

Key result: Weight loss and sodium reduction demonstrated a significant reduction in the incidence of hypertension over several years.

2003

PREMIER Trial

n = 810 · JAMA

Tested

Behavioral interventions including DASH diet plus physical activity

Population

Adults with above-optimal blood pressure or stage 1 hypertension

Comparator

Established advice only

Endpoint

Change in systolic blood pressure

Key result: Comprehensive lifestyle interventions significantly lowered blood pressure and improved hypertension control rates compared to advice alone.

2010

ENLIGHTEN-DIET Trial

n = 144 · Arch Intern Med

Tested

DASH diet combined with weight management

Population

Overweight or obese adults with hypertension

Comparator

Standard dietary advice

Endpoint

Systolic and diastolic blood pressure

Key result: The combination of the DASH diet and weight management was superior to standard care in reducing blood pressure and improving arterial stiffness.

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