DASH vs. Mediterranean Diet on a Salt Restriction Background: A Randomized Controlled Trial

Authors, Journal, Affiliations, Type, DOI

• Christina Filippou, Costas Thomopoulos, Dimitrios Konstantinidis, Eirini Siafi, Fotis Tatakis, Eleni Manta, et al.
• Clinical Nutrition 2023, 42(10): 1807–1816
• First Cardiology Clinic, National and Kapodistrian University of Athens, Hippokration Hospital, Athens, Greece
• Type: Randomized controlled trial (4-arm, single-centre, single-blinded, superiority design)
• DOI: https://doi.org/10.1016/j.clnu.2023.08.011

Overview

This is the first head-to-head RCT directly comparing the BP-lowering effects of the DASH diet versus the Mediterranean diet, both implemented on a background of sodium restriction (<2000 mg/d), against salt restriction alone and a control group in never-treated adults with high-normal BP or grade 1 hypertension. Over 3 months, the MedDiet was superior to DASH for office systolic BP reduction (−3.2 mmHg, P<0.001), but both diets were equivalent on 24h ambulatory BP — the gold-standard measurement for treatment decisions. Both dietary patterns significantly outperformed salt restriction alone. The finding challenges prior network meta-analyses asserting DASH superiority over MedDiet for BP, which were based on indirect comparisons with unequal arms.

Keywords

Hypertension; blood pressure; DASH diet; Mediterranean diet; salt restriction; dietary intervention

Key Takeaways

Study Design

• 4-arm, single-centre, single-blinded RCT; ITT primary analysis; 3-month intervention
• Groups: (1) Control (CG) — general dietary advice only; (2) Salt restriction group (SRG) — Na <2000 mg/d (~87 mmol); (3) DASH + salt restriction (DDG); (4) MedDiet + salt restriction (MDG)
• Goal across all groups: maintain body weight and physical activity unchanged to isolate dietary effects
• Population: Greek adults age 18–65, high-normal BP (SBP 130–139 and/or DBP 85–89 mmHg) or grade 1 hypertension (SBP 140–159 and/or DBP 90–99 mmHg), never drug-treated, no CVD, DM, renal disease, or HMOD
• n=240 enrolled; 204 (85%) completed; withdrawal highest in CG (26.6%)
• Baseline: mean office SBP/DBP 137.7±5.7 / 88.4±5.9 mmHg; mean 24h ambulatory SBP/DBP 132.9±9.4 / 83.1±7.4 mmHg; BMI 29.2 kg/m² (overweight); 48.3% high-normal BP, 51.7% grade 1 hypertension; 66.3% dyslipidaemia

Dietary Intervention Details

• Both DDG and MDG targeted Na <2000 mg/d (same sodium restriction target); individualized meal plans + 45-min counselling sessions monthly
• DASH: 27% kcal from fat, 6% SFA, 150 mg/d dietary cholesterol; K 4700 mg/d, Ca 1250 mg/d, Na 2000 mg/d
• MedDiet: 37% kcal from fat (mainly olive oil), 6% SFA, 150 mg/d dietary cholesterol; K 4200 mg/d, Ca 950 mg/d, Na 2000 mg/d
• Adherence assessed objectively via 24h urine indices (sodium, potassium, magnesium, calcium, phosphorus) and subjectively via food records and validated adherence scores (DASH Adherence Score 0–10; MedDietScore 0–55)
• Adherence improvement confirmed: DASH score +2.3 (absolute); MedDietScore +13.5 (absolute)

Primary Outcome: Office Systolic BP

MedDiet was superior to DASH for office SBP reduction.

Secondary Outcomes: Office DBP and 24h Ambulatory BP

• Office DBP: MDG vs DDG: −1.5 mmHg (95% CI −3.2 to 0.3), P=0.18 — EQUAL
• 24h ambulatory SBP: MDG vs DDG: −1.9 mmHg (95% CI −5.1 to 1.2), P=0.64 — EQUAL
• 24h ambulatory DBP: MDG vs DDG: −2.1 mmHg (95% CI −4.3 to 0.2), P=0.09 — EQUAL (trend only)
• Night-time DBP: MDG vs DDG: −3.1 mmHg (95% CI −5.8 to −0.4), P=0.02 — MedDiet superior
• DASH was NOT superior to salt restriction alone for 24h ambulatory DBP (DDG vs SRG: −1.5 mmHg, P=0.42)
• Odds of hypertension at 3 months: MDG OR 0.02 vs CG; DDG OR 0.03 vs CG; MDG vs DDG NS (P=0.22)

Urinary Mineral Findings

• MDG achieved greater urinary sodium reduction vs SRG; DDG equal to both
• Both DDG and MDG increased urinary potassium and magnesium vs CG and SRG
• Urinary calcium and phosphorus increased only in DDG (reflecting DASH's higher dairy content vs MedDiet)
• Urinary sodium correlated positively with office SBP/DBP changes; potassium and magnesium correlated negatively; calcium negatively with SBP

Key Discussion Points

• MedDiet superiority for office SBP may partly reflect better white-coat effect attenuation; the difference narrows on ambulatory monitoring
• The MedDiet achieved slightly greater sodium excretion than the DASH group — this mineral difference may partly explain the modest office SBP advantage
• Polyphenols from olive oil and anti-inflammatory properties of the MedDiet may provide additional cardiovascular benefits beyond BP reduction per se
• Prior network meta-analysis (Schwingshackl et al.): DASH superior to MedDiet by −3.31 mmHg for SBP — but this was an indirect comparison with unequal arms; the authors conclude those results are not comparable to a head-to-head RCT
• The 24h ambulatory BP result (gold standard for clinical decisions) shows DASH = MedDiet; no practice-changing difference
• A 1 mmHg reduction in SBP correlates with ~2% reduction in fatal/non-fatal CVD events (meta-regression), suggesting clinical relevance of even modest dietary BP effects
• Dietary interventions may reduce CVD risk beyond BP through effects on other risk factors

Limitations of the Document

• Single-centre, predominantly Greek middle-aged overweight population — generalisability limited
• Only 3-month duration; long-term BP effects and hard clinical outcomes not assessed
• Dietary intervention not blinded (impossible by design); Hawthorne effect possible
• Withdrawal higher in CG (26.6%), suggesting possible disappointment bias in the control arm
• Confounding from urinary mineral differences between groups cannot be fully excluded
• No data on lipids, glucose, or other cardiometabolic parameters beyond BP
• Body weight and physical activity intentionally held constant — clinical practice settings involve multiple concomitant lifestyle changes

Key Concepts Mentioned

• concepts/Heart-Healthy-Dietary-Patterns — head-to-head DASH vs MedDiet BP evidence; DASH equivalence on ambulatory BP
• concepts/Metabolic-Syndrome — BP as MetS criterion; dietary BP strategies
• concepts/Hypertension-HMOD — high-normal BP and grade 1 HT as target population; dietary first-line treatment

Key Entities Mentioned

• entities/Hypertension — primary therapeutic target; non-pharmacological management strategies

Wiki Pages Updated

• wiki/sources/dash-meddiet-cn-2023.md — created (this file)
• wiki/concepts/Heart-Healthy-Dietary-Patterns.md — updated with head-to-head DASH vs MedDiet BP data; contradiction updated
• wiki/concepts/Metabolic-Syndrome.md — updated DASH BP section with head-to-head context
• wiki/sourceindex.md — updated
• wiki/wikiindex.md — updated