Hypertension is a primary risk factor for the development of cardiovascular disease and is the leading cause of premature death around the world (approximately 12.8% of global deaths).
An increase in systolic blood pressure (SBP) or diastolic blood pressure (DBP) by 20/10 mmHg will double the risk of cardiovascular disease. Consequently, approaches to reducing BP are necessary.
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Evidence-based diets for BP reduction
The most typical and well-known dietary treatment strategy for BP control is the Dietary Approaches to Stop Hypertension (DASH) diet.
The DASH diet is rich in vegetables, fruits, and low-fat dairy products. It includes the consumption of fish, nuts, legumes, whole grains, vegetables, magnesium, potassium, calcium, and fiber, alongside a moderate restriction in sodium. In the first DASH clinical trial conducted 20 years ago, the DASH diet was shown to reduce SBP and DBP by 5.5 mmHg and 3.0 mmHg.
Moreover, the DASH diet was effective in reducing other cardiovascular risk factors including blood lipids, blood glucose, body weight, and waist circumference. Consequently, it was recommended in the treatment of hypertension.
Evidence of its quality has been shown using a priori diet quality indices. An a priori diet quality index score is a measure of the success of diet adherence. These indices rely on predefined algorithms to quantify food and nutrient intake relative to nutritional recommendations.
The higher the score, the greater the adherence to the predefined diet pattern. These include the Mediterranean dietary school (MDS), diet quality index international (DQI-I), healthy eating index 2015 (HEI-2015), and dietary diversity score (DDS).
In general, dietary components such as vegetables, fruits, and fiber result score highly in a priori-defined dietary index – as such the DASH diet can sustainably create anti-hypertensive effects in adherents.
The second well-promoted and researched diet is the Mediterranean diet, which has many similarities with the DASH dietary principles, but it's generally higher in fat, with a focus on monounsaturated fat derived from oil, seeds, and nuts.
The Prevención con Dieta Mediterránea (PREDIMED) Study examined the effects of the Mediterranean diet with extra-virgin olive oil or nuts relative to a low-fat dietary pattern on cardiovascular disease and blood pressure among 772 men and women between 55 and 80 years.
Compared to the low-fat diet, the Mediterranean diet with olive oil group on the Mediterranean diet with a nuts group showed an average of 5.9 and 7.1 mmHg reductions respectively in SBP.
Similarly, a Cochrane systematic review of Mediterranean diets and cardiovascular risk factors examined 5 trials about reported blood pressure. Despite heterogeneity between the trials which prevented pooling of results, three of the five trials demonstrated significant reductions in both SBP and DBP.
Macronutrient effects in blood-pressure lowering qualities
Strategies for weight loss include manipulation of macronutrients, including fat, carbohydrate, and protein. There is increasing evidence that macronutrients are effective in reducing blood pressure; the largest quantity of evidence for the effect of any of the three macronutrients influence on blood pressure exists for protein.
The effect of protein intake on blood pressure
Observational studies have consistently shown an inverse relationship between dietary protein and blood pressure. Several well-controlled short-term trials have demonstrated this consistent effect of protein supplementations on blood pressure however longer-term data is sparse. The exact mechanisms relating dietary protein intake to blood pressure are unclear, however, several theories have been proposed.
The amino acids glutamate, cysteine, arginine, leucine, taurine, and tryptophan have all been implicated in blood pressure lowering as a result of influencing processes such as insulin resistance, oxidative stress, nitric oxide bioavailability, and the renin-angiotensin-aldosterone system.
L-arginine in particular is a substrate of nitric oxide synthase and supplementations evidence suggests a role for this amino acid in blood pressure reduction. Despite a proven mode of action, results from randomized controlled trials have shown consistent evidence for the safety and efficacy of dietary proteins supplementation. As such, healthcare providers are advised to suggest replacing carbohydrates with protein as part of his dietary strategy to prevent and treat hypertension
The effect of dietary fat on blood pressure
Total dietary fat intake includes saturated omega-3 polyunsaturated, Omega 6 polyunsaturated, and monounsaturated fatty acids. The OmniHeart clinical trial demonstrated that replacement of carbohydrates with dietary fat, search that 37% of daily energy is derived from total fat, of which 21% is derived from monounsaturated fat (predominantly olive oil and canola oil) reduced blood pressure by 2.9 mmHg.
This evidence has been corroborated by a meta-analysis of 9 randomized controlled trials of high monounsaturated fat diets which demonstrated that both SBP and DPB reductions were significantly greater among participants assigned to these diets compared to control diets. In trials focused on omega-3 fats from fish oils, there is a significant reduction in SBP and DBP among participants with hypertension but not those who are normotensive.
The impact of micronutrients on blood pressure
The World Health Organization recommends a maximum of 2.0g per day of sodium, however, the average self-reported daily sodium intake for Americans >2 years of age is 3.6 g. There is strong evidence that dietary sodium and blood pressure are positively linked from a large number of randomized controlled trials.
The well-known DASH and DASH-sodium trials demonstrated the effects of a DASH diet compared to the typical American diet with 3.6g/day vs 2.3 g/day, and 1.2 g/day, with progressively lower blood pressure results.
The converse effect is seen with potassium. A well-established body of evidence demonstrates that a 0.6 g/day increase in potassium results in a 1 mmHg reduction in SBP. Explanations to elucidate the blood pressure-lowering effect of increase dietary potassium include altered membrane potential which results in decreased vascular smooth muscle contraction or restoration of vasorelaxation in the endothelium.
Conversely low levels of potassium have been linked to poor adaptation of the kidney and dysregulated sodium retention and the development of hypertension. This is the result of potassium regulation of ion channel activity as well as its interaction with the renin-angiotensin-aldosterone system.
Other dietary effects
Excessive alcohol consumption is associated with elevated blood pressure and the development of hypertension. However, the association between blood pressure and moderate or low levels of alcohol consumption is less clear. Studies have shown that the relationship between the two may vary by gender, presence of comorbidities, and ethnicity.
An additional dietary factor is a dietary fiber. There is strong evidence that dietary fiber can reduce cholesterol however its association with hypertension is insufficient.
There is a well-established body of research that demonstrates that several dietary components on dietary patterns affect blood pressure. The strongest evidence for managing or lowering blood pressure and preventing hypertension through dietary intervention includes adopting dietary patterns such as the Mediterranean diet or DASH diet.
In general, reducing consumption of saturated fat and total fat, increasing potassium, and limiting the amount of sodium and alcohol in the diet is also linked to positive effects on blood pressure. Both the DASH and Mediterranean diets also show the greatest success in terms of adherence and may be more impactful than substantially reducing intake of any given macronutrients such as fat. Despite the proven benefits of dietary interventions, cultural and societal factors impact whether populations adopt and follow such a diet.
For effective and widespread normotensive BP in populations, public health interventions must consider behavior change incentives and promote access to healthy food choices.
References:
- Appel LJ American Society of Hypertension Writing G. (2009) ASH position paper: dietary approaches to lower blood pressure. J Am Soc Hypertens. doi: 10.1016/j.jash.2009.08.003.
- Svetkey LP, Simons-Morton D, Vollmer WM, et al. (1999) Effects of dietary patterns on blood pressure: subgroup analysis of the Dietary Approaches to Stop Hypertension (DASH) randomized clinical trial. Arch Inter Med. doi:10.1001/archinte.159.3.285.
- Appel LJ, Sacks FM, Carey VJ, et al. (2005) Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids: results of the OmniHeart randomized trial. JAMA. doi: 10.1001/jama.294.19.2455.
- He J, Wofford MR, Reynolds K, et al. (2011) Effect of dietary protein supplementation on blood pressure: a randomized, controlled trial. Circulation. doi: 10.1161/CIRCULATIONAHA.110.009159.
- Teunissen-Beekman KF, van Baak MA. (2013) The role of dietary protein in blood pressure regulation. Curr Opin Lipidol. doi: 10.1097/MOL.0b013e32835b4645.
- Vasdev S, Stuckless J. (2010) Antihypertensive effects of dietary protein and its mechanism. Int J Angiol. doi:10.1055/s-0031-1278362.
- Castaneda-Bueno M, Arroyo JP, Gamba G. (2012) Independent regulation of Na+ and K+ balance by the kidney. Med Princ Pract Int J Kuwait Univ Health Sci Cent. doi:10.1159/000332580.
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