Plant-based diets that allow a limited amount of animal products can help reduce blood pressure  

Gibbs J, Gaskina E, Jia C, et al. The effect of plant-based dietary patterns on blood pressure: A systematic review and meta-analysis of controlled intervention trials J Hypertens. 2021;39:23-37.

Review question

Do plant-based diets reduce blood pressure in adults?

Background

Globally, over one billion people live with high blood pressure (also known as hypertension), a condition that results in nine million deaths every year and contributes to the development of heart disease and stroke. Past meta-analyses have shown that vegan and vegetarian diets may help reduce blood pressure, although positive results for vegan diets were only seen in individuals with a baseline systolic blood pressure of ≥130 mm Hg, which is higher than normal. More research on the effects of plant-based diets on blood pressure—beyond just vegan and vegetarian diets—has since been released. This includes evidence on diets that allow for the consumption of a limited amount of animal products. As a result, a comprehensive systematic review that examines the inclusion and exclusion of animal products in a diet is needed.

How the review was done

This is a systematic review and meta-analysis of 41 studies, the vast majority of which were randomized controlled trials. The studies were published between 1983 and 2019 and included a total of 8416 participants. Key features of the studies:

• Participants were adults between the ages of 25 and 71 who ranged from having normal blood pressure to high blood pressure. Some participants were also living with other health conditions, such as overweight, obesity, type 2 diabetes, and high cholesterol.
• Participants followed one of the following diets: vegan diet, lacto-ovo vegetarian diet, Dietary Approaches to Stop Hypertension (DASH diet), healthy Nordic diet, Mediterranean diet, high-fiber diet, or high-fruit and vegetables diet. All but the vegan diet allowed an often limited consumption of animal products; while also promoting greater consumption of whole grains, legumes, fruits, vegetables, nuts, and seeds. Some participants were asked to not alter their alcohol intake, while others were excluded based on their alcohol intake.
• Researchers evaluated changes in systolic and diastolic blood pressure.
• Results were compared to people in control groups following one of these reference diets: their regular diet, a low fiber diet, the average or standard diet for their population (e.g., Australian, Iranian, Danish, or Western), a low fat diet, a low fruit and vegetable diet, a high protein diet, a weight-reducing diet, conventional advice, the American Diabetic Association diet, a portion controlled diet, the prudent diet, or the Korean Diabetes Association diet.  
• Studies lasted between just over a week to 4 years (i.e., 1.4 – 208 weeks).

What the researchers found

Overall, the review found that plant-based diets can help reduce blood pressure in adults. However, the results varied by diet and outcome (e.g., systolic vs. diastolic). The certainty of the evidence ranged from very low to high. The lower the certainty, the less confidence there is in the results, and the higher the likelihood that future research will have different findings.  

The following diets reduced both systolic and diastolic blood pressure:

• The DASH diet reduced both aspects of blood pressure by a large amount based on high certainty evidence.
• The lacto-ovo vegetation diet reduced systolic blood pressure by a large amount based on high certainty evidence and diastolic blood pressure by a large amount based on moderate certainty evidence.
• The healthy Nordic diet reduced both aspects of blood pressure by large amounts based on moderate certainty evidence. 

The following diet reduced systolic blood pressure only:

• The Mediterranean diet reduced systolic blood pressure by a large amount based on moderate certainty evidence but did not reduce diastolic blood pressure based on moderate certainty evidence.

The following diets did not reduce either systolic or diastolic blood pressure:

• The high fruit and vegetable diet and the high fiber diet based on very low certainty evidence.
• The vegan diet based on low certainty evidence.

These findings imply that diets that allow a limited amount of animal products can be successful in reducing blood pressure; and that the complete removal of animal products from a diet may not be necessary.

Conclusion

Plant-based diets, specifically those that allow some animal products, such as the healthy Nordic, DASH lacto-ovo vegetarian, and Mediterranean diets, can be beneficial in reducing certain aspects of blood pressure in adults.