By Eric Neilson, MD

Assistant Professor, Department of Clinical Foundations at Ross University School of Medicine, Barbados, West Indies

Dr. Neilson reports no financial relationships relevant to this field of study.

SYNOPSIS: A prospective cohort study in the United Kingdom demonstrated that vegetarians have a 22% lower incidence of ischemic heart disease, but a 20% increased incidence of total stroke, mostly related to hemorrhagic stroke, when compared to meat eaters. No difference in ischemic stroke or acute myocardial infarction was found.

SOURCE: Tong TYN, Appleby PN, Bradbury KE, et al. Risks of ischaemic heart disease and stroke in meat eaters, fish eaters, and vegetarians over 18 years of follow-up: Results from the prospective EPIC-Oxford study. BMJ 2019;366:I4897.

Published dietary recommendations often are confusing, controversial, or contradictory. This is especially true for vegetarian diets and red meat consumption, wherein current recommendations vary widely. The Annals of Internal Medicine recently published, with low-certainty evidence, a weak recommendation for adults to continue current processed and unprocessed red meat consumption.¹ The World Health Organization’s International Agency for Research on Cancer lists processed meat in the Group 1, carcinogenic to humans, classification.² American College of Cardiology (ACC)/American Heart Association (AHA) guidelines strongly recommend (Class I, Level A evidence) a diet high in vegetables, fruits, and whole grains, including low-fat dairy, poultry, and fish, with limited red meat.³ Providing patients with clear, unambiguous dietary advice seems to be an impossible mission. Tong et al in BMJ offer evidence that further complicates this conversation. These authors followed nearly 50,000 vegetarians, red meat eaters, and pescatarians over the course of 18 years to monitor stroke and ischemic heart disease outcomes.

Using proportional hazards regression models for associations between diet groups, results indicated that compared to a diet inclusive of red meat, a pescatarian or vegetarian diet is associated with a decreased risk of ischemic heart disease. However, when compared to a diet including red meat, a vegetarian diet is associated with increased risk of total and hemorrhagic stroke. This risk reduction translates to four and 10 fewer incidents of ischemic heart disease per 1,000 persons over 10 years for pescatarians and vegetarians, respectively, compared to red meat eaters (predicted incidents per 1,000 population: 40.4 pescatarians and 36.2 vegetarians vs. 46.2 meat eaters; 95% confidence interval [CI] and P heterogeneity value < 0.001). Vegetarians had three more cases of total stoke per 1,000 persons over 10 years compared to red meat eaters (18.3 vs. 15.4; 95% CI and P heterogeneity value = 0.04). Data indicated that there was no statistically significant increase in stroke incidence for pescatarians. Continued research on larger and more diverse groups of participants and considerations of the effects of specific nutrients associated with variations in diet (e.g., cholesterol, fatty acids, vitamin B12), are critical to determine the underlying mechanisms for the results found in this study. This nutritional study also is complicated by self-reporting, exclusion of high calorie intake, and changes in diet over time, which must be a component in future research. The study supports general ACC/AHA guidelines and indicates the need for physicians to have discussions with patients regarding the risks and benefits of individual dietary considerations.

REFERENCES

1. Johnston B, Zeraatkar D, Han MA, et al. Unprocessed red meat and processed meat consumption: Dietary guideline recommendations from the nutritional recommendations (NutriRECS) consortium. Ann Intern Med 2019. doi:10.7326/M19-1621. [Epub ahead of print].
2. International Agency for Research on Cancer. IARC monographs on the identification of carcinogenic hazards to humans, volumes 1-124. World Health Organization. Available at: https://monographs.iarc.fr/agents-classified-by-the-iarc/. July 16, 2019. Accessed Oct. 19, 2019.
3. Eckel RH, Jakicic JM, Ard JD, et al. 2013 AHA/ACC guidelines on lifestyle management to reduce cardiovascular risk: A report of the American College of Cardiology/American Heart Association task force of practice guidelines. Circulation 2014;129(Suppl 2):S76-S99.