The lowdown on the DASH diet

Guest blogger: Priya Tew RD
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As health professionals know, diet and lifestyle can significantly reduce hypertension – and one of the most effective ways is the Dietary Approaches to Stop Hypertension (DASH) diet.

Why is this important? Let’s start with some stark stats…

Heart and circulatory diseases cause more than 25% of all deaths in the UK – that’s more than 160,000 deaths each year and an average of 450 deaths a day. It’s estimated that around 7.4 million people in the UK are living with cardiovascular disease.

Hypertension increases the risk of heart disease and stroke¹, and is often seen as a ‘silent killer’, responsible for over 50% of heart attacks and strokes². Hypertension affects around 90% of adults over their lifetime, and only about 35% have this well controlled¹. There are no ‘watch out’ symptoms, meaning one in two people with high blood pressure are unaware they have it³.

So, how does the DASH diet help?

What is the DASH diet?

The Dietary Approaches to Stop Hypertension (DASH) diet is not a new concept. It was developed in the 1990s, when the National Institute of Health (NIH) started funding research projects to investigate if specific dietary interventions were useful in treating hypertension.

The DASH diet has similarities with the popular Mediterranean diet in encouraging fruits, vegetables, wholegrains, lean proteins and a lower salt intake – all things that are already part of health messaging and known to be beneficial. But DASH takes it one step further, giving more specific guidance on portions.

The DASH diet consists of:

• 7–8 portions of wholegrains a day
• 4–5 portions of fruit a day
• 4–5 portions of vegetables a day
• 2–3 portions of low-fat dairy a day
• 2 portions or less of lean protein a day (more of a focus on plant proteins)
• Nuts 4–5 times a week
• Reduced salt

There is a wealth of quality evidence showing that following this particular way of eating can lower blood pressure, cholesterol and thus reduce heart disease risks.

DASH lowers blood pressure

As the name suggests, the DASH diet has been shown to significantly reduce blood pressure^4,5. A newly-published (2020)⁵ umbrella review pooled data from 50 systematic reviews and meta-analyses of Randomised Control Trials (RCTs) looking at the efficacy of 12 dietary patterns for lowering blood pressure – namely the DASH, Mediterranean, Nordic, vegetarian, low-salt, low-carbohydrate, low-fat, high-protein, low glycaemic index, portfolio, pulse, and Paleolithic diets.

The review found that the DASH, Nordic, and Portfolio diets all significantly reduced blood pressure, but the DASH diet was associated with the greatest reduction in both Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP) compared to the other dietary patterns. This finding was true for both pre-hypertensive and hypertensive patients⁵.

The reductions in DBP and SBP with the DASH diet are clinically significant, offering a reduction of around 5–8 mmHg in SBP and around 3–4 mmHg in DBP. Studies suggest that a 2 mmHg reduction in SBP and DBP is associated with a 10% lower mortality from stroke and a 7% lower mortality from coronary artery disease^6,7.

Although the DASH diet has been shown to offer the greatest reduction in blood pressure, significant reductions are also seen in Nordic and Portfolio dietary patterns. These diets all share a common theme: they are rich in fruits, vegetables, whole grains, legumes, seeds, nuts, fish and dairy products, and low in processed meats, saturated fat and sweet treats.

So when deciding what might work for a client, it’s a case of there not always being a gold standard way of eating but following an approach that you can adapt to work for the person in front of you.

What about salt?

The original DASH diet developed in 1997 was based on an intake of 3,000mg of sodium (7.5g salt), which is similar to the current average intake in the UK, and higher than UK recommendation of <6g salt per day. Despite the higher sodium content of the original diet, significant reductions to blood pressure were observed.

In the lead up to Salt Awareness Week (8 – 14 March 2021) it is important to highlight the importance of salt reduction for reducing blood pressure.

The DASH-Sodium study was published in 1999⁸ and helped to shape the DASH diet recommendations today. This RCT compared the effects of three levels of sodium intake in a typical American diet (control) or the DASH diet on blood pressure. Participants’ daily sodium intake levels were either high, at 3,300 mg (8g salt), medium at 2,300 mg (5g salt); or low at 1,500 mg (3g salt).

The study found that reducing daily sodium lowered blood pressure for participants on either diet, but the DASH diet lowered blood pressure more than the typical American diet at all three sodium levels. The results show a dose-response, as blood pressure decreased with each reduction of sodium. The conclusion was that following a sodium-reduced DASH diet is more beneficial for lowering blood pressure than following the DASH diet or reducing salt in the diet alone.

What about weight loss for those with high blood pressure?

One of the most commonly-cited risk factors for high blood pressure is being overweight. However, in recent years more and more health professionals are favouring a non-weight centric approach to their practice.

This stems from the belief that improved health behaviours are a more meaningful measure of health than body weight alone, e.g., increased fruit and vegetable intake and physical activity. In fact, research⁹ looking at the efficacy of the DASH diet with and without energy restriction found both subtypes of the diet could significantly reduce blood pressure, indicating the effects of the DASH diet are independent of weight loss.

Additional benefits of the DASH diet

Since its inception, the DASH diet has been studied extensively. Evidence suggests that following this eating pattern has benefits for other health concerns beyond hypertension, including Type 2 Diabetes (T2D)¹⁰ and possibly Gestational Diabetes (GDM)¹¹.

A meta-analysis¹⁰ of 20 articles examining the effect of the DASH diet on glycaemic control found that following the DASH diet could significantly reduce fasting insulin levels. However no beneficial effect was seen for fasting blood glucose or HOMA-IR. The authors concluded that the DASH diet may improve insulin sensitivity independent of weight loss.

Another interesting benefit of the DASH diet is emerging for GDM. In a small trial¹¹, women with GDM followed the DASH diet for four weeks. It was found that following the DASH diet during pregnancy lowered insulin use, reduced caesarean rates and lowered birth weights.

Although there is promising research for the DASH diet in both T2D and GDM, more research is needed.

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The Dash Diet: Lower your blood pressure in just 21 days

If you’re looking for a client/patient-facing information about the DASH diet, Priya has just published a book on the topic. It aims to explain the science behind the DASH diet in an accessible way. It also includes practical tips to help patients to increase fruit and vegetable intake, lower their salt intake and make positive lifestyle changes, including 21 days of meal plans, recipes, and shopping lists.

Further reading

1. British Dietetic Association Fact Sheet
2. Chiavaroli L, Viguiliouk E, Nishi SK, Blanco Mejia S, Rahelić D, Kahleová H, Salas-Salvadó J, Kendall CW, Sievenpiper JL. DASH Dietary Pattern and Cardiometabolic Outcomes: An Umbrella Review of Systematic Reviews and Meta-Analyses 2019 Feb 5;11(2):338. doi: 10.3390/nu11020338. PMID: 30764511; PMCID: PMC6413235.
3. Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, Obarzanek E, Conlin PR, Miller ER 3rd, Simons-Morton DG, Karanja N, Lin PH; DASH-Sodium Collaborative Research Group. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. N Engl J Med. 2001 Jan 4;344(1):3-10. doi: 10.1056/NEJM200101043440101. PMID: 11136953
4. DASH Eating Plan, National Heart, Lung and Blood Institute

References:

1. Houston M.C and Harper K.J (2008). The Journal of Clinical Hypertension 10 (7): 3-11 D.J.A. Jenkins, P.J. Jones et al (2015)Nutrition, Metabolism and Cardiovascular Diseases, Volume 25, Issue 12: 1132-1139
2. Health matters: combating high blood pressure, January 2017
3. Public Health England, Health matters: combating high blood pressure, January 2017
4. Sukhato K, Akksilp K, Dellow A, Vathesatogkit P, Anothaisintawee T. Efficacy of different dietary patterns on lowering of blood pressure level: an umbrella review. Am J Clin Nutr. 2020 Dec 10;112(6):1584-1598.
5. Schwingshackl L, Chaimani A, Schwedhelm C, Toledo E, Pünsch M, Hoffmann G, Boeing H. Comparative effects of different dietary approaches on blood pressure in hypertensive and pre-hypertensive patients: A systematic review and network meta-analysis. Crit Rev Food Sci Nutr. 2019;59(16):2674-2687. doi: 10.1080/10408398.2018.1463967. Epub 2018 May 11. PMID: 29718689.
6. Lewington S, Clarke R, Qizilbash N, Peto R, Collins R. Age-specific relevance of usual blood pressure to vascular mortality: a meta-analysis of individual data for one million adults in 61 prospective studies. Lancet 2002;360(9349):1903–13.
7. Cook NR, Cohen J, Hebert PR, Taylor JO, Hennekens CH. Implications of small reductions in diastolic blood pressure for primary prevention. Arch Intern Med 1995;155(7):701–9.
8. Svetkey LP, Sacks FM, Obarzanek E, Vollmer WM, Appel LJ, Lin PH, Karanja NM, Harsha DW, Bray GA, Aickin M, Proschan MA, Windhauser MM, Swain JF, McCarron PB, Rhodes DG, Laws RL. The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-sodium): rationale and design. DASH-Sodium Collaborative Research Group. J Am Diet Assoc. 1999 Aug;99(8 Suppl):S96-104. doi: 10.1016/s0002-8223(99)00423-x. PMID: 10450301.
9. Saneei P, Salehi-Abargouei A, Esmaillzadeh A, Azadbakht L. Influence of Dietary Approaches to Stop Hypertension (DASH) diet on blood pressure: a systematic review and meta-analysis on randomized controlled trials. Nutr Metab Cardiovasc Dis 2014;24(12):1253–61.
10. Shirani F, Salehi-Abargouei A, Azadbakht L. Effects of Dietary Approaches to Stop Hypertension (DASH) diet on some risk for developing type 2 diabetes: a systematic review and meta-analysis on controlled clinical trials. Nutrition. 2013 Jul-Aug;29(7-8):939-47. doi: 10.1016/j.nut.2012.12.021. Epub 2013 Mar 6. PMID: 23473733.
11. Asemi Z, Samimi M, Tabassi Z, Esmaillzadeh A. The effect of DASH diet on pregnancy outcomes in gestational diabetes: a randomized controlled clinical trial. Eur J Clin Nutr. 2014 Apr;68(4):490-5. doi: 10.1038/ejcn.2013.296. Epub 2014 Jan 15. PMID: 24424076.