This new study potentially changes that sunny view of the diet after researchers looked at the rates of heart disease and stroke in more than 48,000 people who ate vegetarian diets, those who included fish or "pescatarians," and those who ate a diet with meat.
Over 18 years, vegetarians had lower risk of heart disease, but they had a 20% higher risk of any kind of stroke. When researchers analyzed hemorrhage strokes, or strokes caused by a brain bleed, vegetarians had 43% higher risk than meat eaters.
Dieticians caution that studies like this do not prove that the vegetarian diet causes higher stroke risk, just that the two are linked.
"I do feel like we have to take into account that it is an observational study, so we can't establish causality between eating a plant based diet and increased risk of stroke," said Maya Mosquera, a clinical registered dietician who specializes in cardiac rehabilitation, in an interview with ABC News. Mosquera was not associated with the study.
How could a vegetarian diet be connected to stroke? At this time, it is unknown, but both dieticians offered different theories.
"The vegetarian section included people who ate eggs. There is some research that including eggs in your diet increase the risk of stroke," said Mosquera.
"Eggs also contain a certain type of nutrient that is processed into [a molecule called] TMAO that we know increases plaque buildup in the heart. There might be some correlation of what TMAO is doing in the heart and the brain," Mosquera said, though she added this is speculation. Plaque causes narrowing in arteries, which can contribute to stroke.
Feller's theory is that "it could be changes in the omega 3 fatty acids in combination with vitamin B12" in a vegetarian and vegan diet.
The researchers of the British study did collect data on other factors that can affect heart disease and stroke, including smoking, alcohol consumption, physical activity and hormone use (such as birth control or hormone replacement therapy after menopause). But accounting for these other factors did not change the results -- vegetarians were still more likely to have strokes than meat-eaters.
One issue is that a vegetarian diet today means something different than it did 20 years ago.
"What has been available to vegetarians has completely changed. If people are eating vegetarian convenience diet, or foods that are packaged, that is different than a whole or minimally processed diet," said Feller.
So, what diet should you be eating?
"The best diet is something that is sustainable, feels good for you, and is good for your health. There is no one size fits all," said Feller.
Mosquera added, "Historically the biggest thing I can say is that fruits and vegetables are not bad for your health. Not much could go wrong with increasing fruits and vegetables in your diet."
As a reminder, any dramatic changes to your diet should be discussed with a doctor and/or registered dietician. Plant-only diets that exclude processed grains are susceptible to low vitamin B12 intake. Severe vitamin B12 deficiency can cause nerve damage and blindness, as previously reported by ABC News.
Sejal Parekh, MD is a pediatrician in San Diego, currently working in the ABC News Medical Unit.