Abstract
The consumption of strict vegetarian diets with no animal products is associated with low blood pressure (BP). It is not clear whether less strict plant-based diets (PBDs) containing some animal products exert a similar effect. The main objective of this meta-analysis was to assess whether PBDs reduce BP in controlled clinical trials. Methods: We searched Cumulative Index to Nursing and Allied Health Literature, Medline, Embase, and Web of Science to identify controlled clinical trials investigating the effect of PBDs on BP. Standardized mean differences in BP and 95% confidence intervals were pooled using a random effects model. Risk of bias, sensitivity, heterogeneity, and publication bias were assessed. Results: Of the 790 studies identified, 41 clinical trials met the inclusion criteria (8416 participants of mean age 49.2 years). In the pooled analysis, PBDs were associated with lower SBP [Dietary Approach to Stop Hypertension -5.53 mmHg (95% confidence intervals -7.95,-3.12), Mediterranean -0.95 mmHg (-1.70,-0.20), Vegan -1.30mmHg (−3.90,1.29), Lacto-ovo vegetarian -5.47 mmHg (-7.60,-3.34), Nordic -4.47 mmHg (−7.14,−1.81), high-fiber -0.65 mmHg (-1.83,0.53), high-fruit and vegetable -0.57 mmHg (-7.45,6.32)]. Similar effects were seen on DBP. There was no evidence of publication bias and some heterogeneity was detected. The certainty of the results is high for the lacto-ovo vegetarian and Dietary Approach to Stop Hypertension diets, moderate for the Nordic and Mediterranean diets, low for the vegan diet, and very low for the high-fruit and vegetable and high-fiber diets. Conclusion: PBDs with limited animal products lower both SBP and DBP, across sex and BMI.
Generated Summary
This meta-analysis and systematic review of controlled clinical trials investigated the effect of plant-based dietary patterns (PBDs) on blood pressure (BP). The study aimed to assess whether PBDs, including those with some animal products, reduce BP in controlled clinical trials. The research involved searching databases like Cumulative Index to Nursing and Allied Health Literature, Medline, Embase, and Web of Science. The analysis included 41 clinical trials meeting specific criteria, with a total of 8416 participants. The primary outcome was the change in systolic and diastolic blood pressure (SBP and DBP) associated with different PBDs. The study evaluated the risk of bias, heterogeneity, and publication bias using a random effects model. The interventions included various PBDs such as the DASH diet, vegan diet, Mediterranean diet, and others. The study also included a standardized control diet analysis to compare the effects of PBDs versus standard control diets on BP.
Key Findings & Statistics
- The study identified 41 clinical trials meeting inclusion criteria, involving 8416 participants.
- PBDs were associated with lower SBP:
- Dietary Approach to Stop Hypertension (DASH): -5.53 mmHg (95% confidence intervals -7.95, -3.12)
- Mediterranean: -0.95 mmHg (-1.70, -0.20)
- Vegan: -1.30 mmHg (-3.90, 1.29)
- Lacto-ovo vegetarian: -5.47 mmHg (-7.60, -3.34)
- Nordic: -4.47 mmHg (-7.14, -1.81)
- High-fiber: -0.65 mmHg (-1.83, 0.53)
- High-fruit and vegetable: -0.57 mmHg (-7.45, 6.32)
- Similar effects were observed on DBP.
- The healthy Nordic diet was associated with a mean reduction in SBP (-4.47 mmHg; 95% CI, -7.14 to −1.81; P=0.001) and DBP (-2.32mmHg; 95% CI, -3.83 to -0.82; P=0.002).
- Consumption of the high-fruit and vegetables diet was associated with a mean reduction in SBP (-0.57 mmHg; 95% CI, -7.45 to −6.32) and DBP (-0.96mmHg; 95% CI, -3.08 to −1.15).
- Consumption of the high-fiber diet was associated with a mean reduction in SBP (-0.65 mmHg; 95% CI, −1.83 to 0.53) and DBP (-1.02 mmHg; 95% CI, −3.86 to −1.82).
- The certainty of the results was high for the lacto-ovo vegetarian and DASH diets, moderate for the Nordic and Mediterranean diets, low for the vegan diet, and very low for the high-fruit and vegetable and high-fiber diets.
- When compared with a standardized control diet, PBDs were associated with a mean reduction in SBP (-4.29mmHg; 95% CI, −6.27 to −2.31; P<0.0001) and DBP (-2.79mmHg; 95% CI, -4.33 to −1.24; P=0.0004).
- For SBP and DBP, respectively (Supplementary Table S5, http://links.lww.com/HJH/B430). The certainty of this evidence is very low (Table 3).
Other Important Findings
- The main objective was to assess whether PBDs reduce BP in controlled clinical trials.
- The study found that plant-based dietary patterns reduce both SBP and DBP.
- The DASH diet encourages the consumption of fruits, vegetables, whole grains, nuts and seeds, and low-fat dairy products and limits the intake of sweets, saturated fat, and sodium.
- The Mediterranean diet main components are daily consumption of vegetables, fruit, whole grains, olive oil, weekly consumption of legumes, nuts, fish, dairy, and eggs, and limited intake of meat.
- Vegan diets consist of plant foods exclusively.
- The meta-regression identified age as a potential source of heterogeneity in the DBP mean differences obtained from the clinical trials investigating the Mediterranean diet (ẞ coefficient, 0.081; P=0.049)
Limitations Noted in the Document
- There was a low number of clinical trials investigating the healthy Nordic diet, high-fiber diet, and high-fruit and vegetables diet.
- The review carried forward the design limitations of the included clinical trials, including small sample sizes.
- The clinical trials were limited by the lack of blinding of study personnel due to the nature of dietary interventions, making double blinding not possible.
- Some of the clinical trials did not adjust the BP outcomes for confounding factors.
- The food and nutrient compositions of the diets used in each clinical trial varied, so the effect of individual nutrients could not be identified.
Conclusion
The study concludes that PBDs, including those with some animal products, are associated with lower SBP and DBP across sex and BMI. The results suggest that the mean reduction in DBP associated with the consumption of the Mediterranean diet is less pronounced among older individuals. The healthy Nordic, ovo-lacto vegetarian, and DASH diets are more effective at reducing BP than the Mediterranean diet. The DASH diet was implemented with either a fixed moderate sodium consumption or with tips given to participants to reduce sodium consumption. The authors note that, “the vegan diet did not significantly reduce BP; however, the certainty of this result is low.” The study suggests that complete eradication of animal products from one’s diet is not necessary to produce significant improvements in BP, and these diets can be considered as achievable lifestyle modifications for those trying to lower their BP. The researchers highlight that the high certainty of the results for the lacto-ovo vegetarian and DASH diets and low certainty for the vegan diet. Overall, the study provides evidence to support that plant-based diets are effective in lowering BP. The study suggests that increasing fruit and vegetable consumption is sufficient to produce a significant reduction in BP, and that it is imperative that further controlled trials are conducted. The study also notes that, “a shift towards healthy diets globally requires focus on environmental sustainability of food production and health consequences of final consumption, requiring multisectoral actions, science and evidence-gathering and a full range of policy changes.”