We might have labeled meat-eaters as artery-clogged heathens, constantly mere seconds away from a heart attack, but according to one recent study, they might have one thing going for them: Compared to vegetarians, omnivores could be less likely to have a stroke.
Although it goes against all our better judgment about what it means to be a healthy eater, medical professionals say there’s a mix of possible explanations for the link, while others, predictably, think there’s not truly a link at all. In hopes of an explanation, we asked doctors and nutritionists from a variety of different backgrounds about their thoughts on the study, published in the British Medical Journal last month. Here’s what they had to say.
Tammy Tong, nutritional epidemiologist at the University of Oxford and primary author of the study: We monitored 48,188 participants in the EPIC-Oxford study for an average of 18 years, and found that within this cohort, people who were pescetarians and vegetarians had 13 percent and 22 percent lower risks of coronary heart disease, respectively, than the meat-eaters. But the vegetarians may have a higher risk of stroke (20 percent) than the meat-eaters, which was mostly due to a higher risk of hemorrhagic stroke. In terms of absolute numbers, however, this was equivalent to ten fewer cases of coronary heart disease and three more cases of total stroke in vegetarians than the meat-eaters, in every 1,000 people consuming these diets over 10 years. This indicates that the higher risk of stroke in vegetarians is still small compared to the lower risk of coronary heart disease.
The lower risks of coronary heart disease is likely at least partly due to the lower BMI, lower blood pressure, lower blood cholesterol and lower rates of diabetes linked to pescetarian or vegetarian diets. For the higher risk of stroke, the mechanisms are less clear, but some recent evidence (reference can be found in the original publication) suggests that while low cholesterol levels is protective against both heart disease and ischaemic stroke, very low levels may be linked to higher risk of hemorrhagic stroke, the subtype found to be higher in the vegetarians.
Vegetarians and vegans might also have low levels of some nutrients, such as vitamin B12, which is only naturally available from animal foods, but also available in fortified foods or supplements. Some research has suggested there may be a link between B12 deficiency and higher stroke risk via raised homocysteine levels, but the evidence isn’t conclusive.
Summer Yule, MS, RDN, nutrition communications specialist: I don’t think the association found in this study should necessarily discourage someone from having a vegetarian diet. However, this study is a great example that shows how no one special dietary pattern is a magic bullet that will eliminate all health risks in all individuals who adhere to it. The link between lower blood levels of cholesterol and the increased risk of hemorrhagic stroke has been recognized for a while — many vegetarians do have lower blood lipid levels. However, the reduction of heart disease risk associated with lower blood cholesterol outweighs the increased risk of hemorrhagic stroke for most individuals.
The words “vegetarian” and “omnivore” don’t actually tell us anything about the quality of the diet, so we cannot say based on those words alone which is healthier. If a person becomes a vegetarian and replaces nutrient-rich meats with sugar-laden dessert foods, that wouldn’t be a health-promoting change. On the other hand, a vegetarian with a diet primarily of minimally processed whole foods (dairy, eggs, vegetables, fruits, whole grains, legumes, nuts, and seeds) has a far more optimal dietary pattern than an omnivore who is consuming the standard American diet.
Joel Fuhrman, family physician and author of The End of Heart Disease: There are two types of strokes — ischemic, or embolic, and hemorrhagic. The ischemic stroke, caused by a clot, has the same risk factors as a heart attack, i.e., a high intake in animal-based foods and animal-based fats, and processed foods. But then there’s the hemorrhagic stroke, caused by a bleed, not by a clot, and that can occur in those who don’t have high cholesterol and who don’t have plaque build-up in their blood vessels. Those with very low cholesterol have been found to have a higher risk of hemorrhage, too.
In fact, it may be that when a blood vessel has no plaque (due to a healthier diet, that is, not atherogenic), it’s more vulnerable to endothelial injury and microvascular bleeds from the effects of chronic high salt intake. Salt damages the lining of our blood vessels and doesn’t merely raise blood pressure, it increases the risk of both types of strokes.
What I’m saying here is that as you eat a more plant-based diet and keep your cholesterol down to avoid heart disease and ischemic strokes, it may be even more important to watch your salt intake, to protect against the possibility of a hemorrhage caused by the high salt intake effect on a native vessel that isn’t thickened or coated with plaque.
Bret Scher, medical director at Diet Doctor: The most important thing about interpreting the study is that it’s a retrospective observational trial, which means we have all this data, then go back and crunch the data and look for associations. So they found an association between vegetarians and hemorrhagic strokes: These aren’t strokes where blood clots block the blood flow to the brain, this is a specific type of stroke where blood leaks out of the blood vessels in your brain. It’s very different than what people think of as a regular stroke.
A study can show an association, but it doesn’t prove anything. It doesn’t say that because these people were vegetarians, that they had a stroke. The vegetarians could also have other health choices or activities that can increase the risk of stroke.
The other part of the study showed that those who eat meat had a higher risk of cardiovascular disease and cardiovascular death. There’s this concept called “healthy user bias” where, in the 1990s, when these people were being recruited, the underlying belief was that eating meat was bad for your health. So people who were eating more meat also likely had other unhealthy behaviors. The data showed that they were more likely to smoke, less likely to exercise, more likely to have high blood pressure, more overweight, so you can’t say it was the meat that caused increase cardiovascular disease. So it goes both ways, in terms of the weakness of drawing conclusions.
Are there other mechanisms for why this could be? People hypothesize that when you lower someone’s LDL cholesterol, studies show that there’s a small but statistically significant increased risk of hemorrhagic stroke. So it could be that vegetarians have lower LDL and that’s why they have an increased risk of stroke. It doesn’t prove it, but that’s what people are hypothesizing. All we know is that there’s an association.
My biggest complaint with nutritional research is that we try to make too strong of a conclusion based on weak evidence. What we can possibly take away from this is that vegetarians were healthier at the baseline, and therefore, had lower risk of cardiovascular disease, but did have a very small increased risk for stroke. When we look at the next step, what can they do to prevent that? There’s no good intervention for it.
At the same time, I wouldn’t dissuade people from being vegetarian because it’s such a small association. Being vegetarian has to be part of an overall healthy lifestyle. There are plenty of unhealthy vegetarians –– french fries are vegetarian, sugary desserts are vegetarian. That’s why, at Diet Doctor, we try to encourage low-carb vegan and vegetarian options. Because again, being vegetarian can’t be assumed by default to be healthy just because it’s vegetarian.