Therapeutics
Review: Vegetarian diets reduce systolic and diastolic blood pressure more than omnivorous diets
Yokoyama Y, Nishimura K, Barnard ND, et al. Vegetarian diets and blood pressure: a meta-analysis. JAMA Intern Med. 2014;174:577-87.
Clinical impact rating: F ★★★★★✩✩ Question
Commentary
Do vegetarian diets affect blood pressure (BP) in adults?
It is difficult to argue against the potential healthfulness of vegetarian or near-vegetarian diets, and many studies support their health value (1). The review by Yokoyama and colleagues contributes additional data, but of limited value. The improvements in BP, although statistically significant, were not clinically impressive on average; the combined sample size from RCTs was small; and all but 1 RCT was published before 2000 (although many of the observational studies were more recent).
Review scope Included studies compared a vegetarian (generally excluding or rarely including meat), semivegetarian (rarely including meat), vegan (excluding all animal products), or vegetarian diet that included some animal products: dairy (lacto), eggs (ovo), or fish (pesco), with a referent or control diet in adults > 20 years of age. Exclusion criteria included studies of twins and use of multiple interventions. Outcomes were systolic BP (SBP) and diastolic BP (DBP).
Review methods MEDLINE and Web of Science (both to Nov 2013) and reference lists were searched for controlled trials or observational studies. 7 trials (n = 311) and 32 observational studies (n = 21 604) met selection criteria. This abstract reports results of the 7 controlled trials (mean age 38 to 54 y, follow-up 6 to 52 wk, mean baseline SBP 118 to 155 mm Hg, mean baseline DBP 76 to 100 mm Hg), 6 of which were randomized controlled trials (RCTs) (n = 198). All trials were unblinded, and 3 used a crossover design. 1 trial included patients receiving medications for hypertension, and 6 trials provided food. Studies compared vegan (2 trials), lactovegetarian (1 trial), and lacto-ovo-vegetarian (4 trials) diets with omnivorous diets.
Main results Meta-analysis of controlled trials showed that vegetarian diets reduced SBP and DBP more than omnivorous diets (Table). Results from 32 observational studies were consistent with these findings.
Conclusion Vegetarian diets reduce systolic and diastolic blood pressure in adults more than omnivorous diets. Source of funding: Japan Society for the Promotion of Science Fellows. For correspondence: Dr. Y. Yokoyama, National Cerebral and Cardiovascular Center, Osaka, Japan. E-mail yyokoyama-kyt@ umin.ac.up. ■ Vegetarian diets vs omnivorous diets in adults* Outcomes
Number of trials (n)
Mean difference, mm Hg (95% CI), at 6 to 52 wk
Systolic blood pressure
7 (311)
−4.8 (−6.6 to −3.1)
Diastolic blood pressure
7 (311)
−2.2 (−3.5 to −1.0)
*Abbreviations defined in Glossary. Pooled estimates are based on a random-effects model.
17 June 2014 | ACP Journal Club | Volume 160 • Number 12 Downloaded From: http://annals.org/ by a University of York User on 11/21/2016
Although studies of multiple interventions (e.g., lifestyle plus dietary interventions) were supposed to be excluded, this does not seem to be the case. For example, the largest included trial provided participants in the intervention group with nutrition counseling, group support meetings, cooking demonstrations, interaction with physicians, grocery store tours, and other “practical tools,” in addition to the prescribed vegan diet; control participants were simply asked to continue their habitual diets and did not appear to receive any other intervention (2). It is possible that any combination of these resources, interventions, and supports was responsible for the reported improved health outcomes. All trials were unblinded, an understandably challenging hurdle of study design, but nonetheless an important limitation given the fervor behind vegetarianism and veganism, which can bias the data. 6 of the 7 trials were of short duration: 4 trials lasted just 6 weeks, and only 1 trial lasted ≥ 6 months. Compliance with restrictive diets of any kind generally wanes after the first few weeks or months. Indeed, in the single trial that lasted more than 22 weeks, the vegetarian diet group had no improvement in SBP or DBP by the end of the study. A more valuable use of resources would be to investigate how to support ongoing and long-term use of healthful eating patterns— vegetarian or not—and how to address barriers that limit practical use of such dietary patterns, such as the high cost of produce. Ultimately, the meta-analysis by Yokoyama and colleagues doesn’t change our general recommendations that healthful, plant-based foods are valuable for good health. If you’d like to “go vegetarian,” do it. But you don’t necessarily need to follow a restrictive or strict vegetarian diet to be healthy. We hope future studies will help to further refine (or perhaps challenge) this age-old advice. Scott Kahan, MD, MPH Lawrence J. Cheskin, MD Johns Hopkins Bloomberg School of Public Health Baltimore, Maryland, USA References 1. Craig WJ, Mangels AR; American Dietetic Association. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc. 2009;109:1266-82. 2. Ferdowsian HR, Barnard ND, Hoover VJ, et al. A multicomponent intervention reduces body weight and cardiovascular risk at a GEICO corporate site. Am J Health Promot. 2010;24:384-7.
© 2014 American College of Physicians
JC3
Review: Vegetarian diets reduce systolic and diastolic blood pressure more than omnivorous diets
Yokoyama Y, Nishimura K, Barnard ND, et al. Vegetarian diets and blood pressure: a meta-analysis. JAMA Intern Med. 2014;174:577-87.
Clinical impact rating: F ★★★★★✩✩ Question
Commentary
Do vegetarian diets affect blood pressure (BP) in adults?
It is difficult to argue against the potential healthfulness of vegetarian or near-vegetarian diets, and many studies support their health value (1). The review by Yokoyama and colleagues contributes additional data, but of limited value. The improvements in BP, although statistically significant, were not clinically impressive on average; the combined sample size from RCTs was small; and all but 1 RCT was published before 2000 (although many of the observational studies were more recent).
Review scope Included studies compared a vegetarian (generally excluding or rarely including meat), semivegetarian (rarely including meat), vegan (excluding all animal products), or vegetarian diet that included some animal products: dairy (lacto), eggs (ovo), or fish (pesco), with a referent or control diet in adults > 20 years of age. Exclusion criteria included studies of twins and use of multiple interventions. Outcomes were systolic BP (SBP) and diastolic BP (DBP).
Review methods MEDLINE and Web of Science (both to Nov 2013) and reference lists were searched for controlled trials or observational studies. 7 trials (n = 311) and 32 observational studies (n = 21 604) met selection criteria. This abstract reports results of the 7 controlled trials (mean age 38 to 54 y, follow-up 6 to 52 wk, mean baseline SBP 118 to 155 mm Hg, mean baseline DBP 76 to 100 mm Hg), 6 of which were randomized controlled trials (RCTs) (n = 198). All trials were unblinded, and 3 used a crossover design. 1 trial included patients receiving medications for hypertension, and 6 trials provided food. Studies compared vegan (2 trials), lactovegetarian (1 trial), and lacto-ovo-vegetarian (4 trials) diets with omnivorous diets.
Main results Meta-analysis of controlled trials showed that vegetarian diets reduced SBP and DBP more than omnivorous diets (Table). Results from 32 observational studies were consistent with these findings.
Conclusion Vegetarian diets reduce systolic and diastolic blood pressure in adults more than omnivorous diets. Source of funding: Japan Society for the Promotion of Science Fellows. For correspondence: Dr. Y. Yokoyama, National Cerebral and Cardiovascular Center, Osaka, Japan. E-mail yyokoyama-kyt@ umin.ac.up. ■ Vegetarian diets vs omnivorous diets in adults* Outcomes
Number of trials (n)
Mean difference, mm Hg (95% CI), at 6 to 52 wk
Systolic blood pressure
7 (311)
−4.8 (−6.6 to −3.1)
Diastolic blood pressure
7 (311)
−2.2 (−3.5 to −1.0)
*Abbreviations defined in Glossary. Pooled estimates are based on a random-effects model.
17 June 2014 | ACP Journal Club | Volume 160 • Number 12 Downloaded From: http://annals.org/ by a University of York User on 11/21/2016
Although studies of multiple interventions (e.g., lifestyle plus dietary interventions) were supposed to be excluded, this does not seem to be the case. For example, the largest included trial provided participants in the intervention group with nutrition counseling, group support meetings, cooking demonstrations, interaction with physicians, grocery store tours, and other “practical tools,” in addition to the prescribed vegan diet; control participants were simply asked to continue their habitual diets and did not appear to receive any other intervention (2). It is possible that any combination of these resources, interventions, and supports was responsible for the reported improved health outcomes. All trials were unblinded, an understandably challenging hurdle of study design, but nonetheless an important limitation given the fervor behind vegetarianism and veganism, which can bias the data. 6 of the 7 trials were of short duration: 4 trials lasted just 6 weeks, and only 1 trial lasted ≥ 6 months. Compliance with restrictive diets of any kind generally wanes after the first few weeks or months. Indeed, in the single trial that lasted more than 22 weeks, the vegetarian diet group had no improvement in SBP or DBP by the end of the study. A more valuable use of resources would be to investigate how to support ongoing and long-term use of healthful eating patterns— vegetarian or not—and how to address barriers that limit practical use of such dietary patterns, such as the high cost of produce. Ultimately, the meta-analysis by Yokoyama and colleagues doesn’t change our general recommendations that healthful, plant-based foods are valuable for good health. If you’d like to “go vegetarian,” do it. But you don’t necessarily need to follow a restrictive or strict vegetarian diet to be healthy. We hope future studies will help to further refine (or perhaps challenge) this age-old advice. Scott Kahan, MD, MPH Lawrence J. Cheskin, MD Johns Hopkins Bloomberg School of Public Health Baltimore, Maryland, USA References 1. Craig WJ, Mangels AR; American Dietetic Association. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc. 2009;109:1266-82. 2. Ferdowsian HR, Barnard ND, Hoover VJ, et al. A multicomponent intervention reduces body weight and cardiovascular risk at a GEICO corporate site. Am J Health Promot. 2010;24:384-7.
© 2014 American College of Physicians
JC3
