Meat-free diets for heart health: Yay or nay?
Vegetarian and pescetarian diets are associated with a lower risk of ischaemic heart disease compared with a diet that include meat, according to the longitudinal EPIC*-Oxford study with 18 years of follow-up.
However, vegetarian diet was also associated with a higher rate of stroke compared with a meat-based diet — calling for a double take on the perceived health benefits of going vegetarian.
As the researchers noted, “Vegetarian and vegan diets have become increasingly popular in recent years”, but the full extent of potential health benefits or hazards have yet to be understood.
In the prospective longitudinal EPIC-Oxford cohort study, 48,188 participants (mean age 45 years) who were free of cardiovascular (CV) disease at baseline were categorized into three diet groups: meat eaters (n=24,428), pescetarians (n=7,506), and vegetarians (n=16,254). [BMJ 2019;366:l4897]
Over 18.1 years of follow-up, incident cases of ischaemic heart disease occurred in 2,820 participants while incident stroke was reported in 1,072 individuals.
After adjusting for sociodemographic variables, lifestyle, and medical history, vegetarians and pescetarians were 22 percent (hazard ratio [HR], 0.78) and 13 percent (HR, 0.87) less likely to have ischaemic heart disease compared with meat eaters, respectively (p<0.001 for heterogeneity).
This, according to the researchers, was equivalent to 10 and six fewer cases of ischaemic heart disease in vegetarians and pescetarians than meat eaters, respectively per 1,000 population over 10 years.
As the associations seen in vegetarians were partly attenuated after further adjustment for self-reported high blood cholesterol, hypertension, diabetes, and BMI, this indicates that these factors may have contributed to some extent to the cardioprotective benefits of a vegetarian diet.
“[The lower risk of ischaemic heart disease may] be partly attributed to lower concentrations of LDL-C associated with meat-free diets,” suggested the researchers.
By contrast, the rates of total stroke were 20 percent higher among vegetarians than meat eaters (HR, 1.20, 95 percent confidence interval [CI], 1.02–1.40), translating to three more stroke cases per 1,000 population over 10 years.
The difference was mainly driven by a higher rate of ischaemic heart disease in vegetarians vs meat eaters (HR, 0.78, 95 percent CI, 0.70–0.87; p<0.001 for heterogeneity). Furthermore, the association for stroke was not attenuated even after further controlling for disease risk factors, which according to the researchers, suggest “that some factors associated with animal food consumption might be protective for stroke.”
Although the mediating factors behind the association for stroke have yet to be determined, the researchers believed that the lower levels of certain vitamins and nutrients such as polyunsaturated fatty acids in a vegetarian diet may play a role.
“[However,] vegetarians and others should keep the reported stroke risk in perspective,” wrote Professors Mark Lawrence and Sarah McNaughton from Deakin University in Geelong, Australia, in an accompanying editorial. “It is based on results from just one study, and the increase is modest relative to meat eaters.” [BMJ 2019;366:l5272]
“Relevance to vegetarians worldwide must also be considered. Participants were all from the UK where dietary patterns and other lifestyle behaviours are likely to differ from those prevalent in low- and middle-income countries, where most of the world’s vegetarians live,” they highlighted.
While plant-based diets have gained increasing popularity for health as well as environmental sustainability reasons, Lawrence and McNaughton said “shifting towards plant-based dietary patterns … does not necessarily mean becoming a vegetarian.”
“[With] dietary guidelines increasingly recognizing the need to reduce intake of ultra-processed foods … this recommendation is particularly relevant to vegetarians who might be unaware that many foods marketed to vegetarians are ultra-processed,” they pointed out.