Researchers found that pescatarians may face a lower heart disease risk than meat-eaters but without increased likelihood of stroke, too. They have a theory about why.
Diets that call for avoiding either meat or all animal products get a lot of buzz for being healthy and contributing to weight loss. But there may be a catch to these diets, called vegetarian and vegan diets, respectively: a higher risk for a certain type of stroke.
In a study published in September 2019 in the BMJ, researchers observed that non-meat-eaters had a 22 percent lower risk for coronary artery disease, a type of heart disease, but a 20 percent higher risk for hemorrhagic stroke. At the same time, pescatarians, who eat fish but not meat, had the same risk of stroke but a 13 percent lower risk for heart disease compared with the meat eaters. (The authors did not formally compare these risks in fish eaters versus vegetarians.) To draw their results, the reasearchers followed 48,000 people in Great Britain for nearly 18 years.
“Our findings indicate that the vegetarians had higher stroke risk than meat eaters, mostly due to a subtype of stroke called hemorrhagic stroke that is related to bleeding in the brain,” says lead researcher Tammy Tong, PhD, a nutritional epidemiologist at the Nuffield Department of Population Health at the University of Oxford in England.
The study didn’t determine why, but past research offers a clue: Nutrient deficiencies common among non-meat-eaters may be tied to a higher risk for hemorrhagic stroke.
“A low cholesterol level is known to be protective against heart disease and ischemic stroke,” says Dr. Tong, “but some recent evidence suggests that low cholesterol may be linked to higher risk of hemorrhagic stroke, the subtype of stroke found to be higher in the vegetarians.” For example, a study published in May 2019 in Neurology found that women who had LDL cholesterol levels — considered the “bad” type of cholesterol — that were 70 milligrams per deciliter (mg/dL) or lower were twice as likely to have this type of stroke than women with levels that ranged from 100 to 130 mg/dL.
A Closer Look at the Merits of Plant-Based Eating
A seemingly unshakable health halo has long encircled diets that focus on reducing or avoiding meat and other animal products. The validity of this approach exceeds that of celebrity-endorsed diet fads, too: Research has shown that plant-based eating styles, such as vegetarian and vegan diets, may reduce the risk for, and potentially help treat, obesity, heart disease, and type 2 diabetes. For example, studies cited in an article published in the Summer 2016 issue of The Permanente Journal suggested those health benefits and more.
Yet if followed improperly, vegan and vegetarian diets can also pose an elevated risk for deficiencies of nutrients such as vitamin B12. Tong says some previous studies have suggested that low B12 levels in vegetarians may contribute to higher stroke risk, but the evidence is not conclusive.
The important thing is to keep this potential health risk of plant-based eating in perspective.
According to the American Stroke Association, the most common type of hemorrhagic stroke occurs when a blood vessel in the brain bursts and leaks blood into surrounding tissue. The bleeding causes brain cells to die and the affected part of the brain stops working correctly. But almost 9 out of 10 are not hemorrhagic but ischemic, according to the Centers for Disease Control and Prevention (CDC). An ischemic stroke happens when blood flow through an artery is blocked, usually by a blood clot.
How Eating Fish May Help Lower the Risk for Stroke
Sarah Samaan, MD, a cardiologist with Baylor Scott and White Legacy Heart Center in Plano, Texas, suggests that vegetarians and vegans also may not be getting enough healthy omega-3 fatty acids in their diet. Fatty fish, such as salmon, herring, sardines, and trout, offer omega-3 fatty acids, and the American Heart Association recommends eating two servings of these types of fish each week to reduce stroke and heart disease risk.
“Although some nuts and oils provide omega-3s, the plant-based forms of this nutrient are not used very efficiently by the body, whereas we are able to process omega-3s from fish quite readily,” says Dr. Samaan, who is also the author of DASH (Dietary Approaches to Stop Hypertension) Diet for Dummies. “It is likely that the lack of certain animal-based nutrients, such as healthy fats, puts vegans and vegetarians at risk for hemorrhagic stroke.”
She underscores that fish tends to be lower in cholesterol than meat and less likely to cause inflammation of the blood vessels.
“The results appear to correspond to the lower risk of heart disease in pescatarians,” says Samaan, whose preferred diet for about the past 30 years has been a fish- and plant-based Mediterranean diet. “While there is more than one way to eat clean and healthy, the preponderance of nutritional research supports this diet when it comes to heart health, brain health, and cancer risk reduction.”
Among Plant-Based Dieters, the Higher Stroke Risk Was Small Compared With Their Lower Heart Disease Risk
The researchers also stress that, among the vegetarians and vegans, the higher risk from stroke in absolute numbers was small compared with the lower risk of heart disease. Over 10 years, there were 10 fewer cases of coronary heart disease in every 1,000 people, but 3 more cases of stroke per 1,000 in the vegetarians, according to the study.
“It is important to keep in mind the absolute risk differences of the two outcomes reported here, which suggest the higher risk from stroke is small compared with the lower risk from coronary heart disease,” Tong says.
The investigation results still suggest that a vegetarian or vegan diet may have many heart-healthy benefits, which is in line with advice from the American Heart Association.
“The lower risk of heart disease [among vegetarians] is likely related to the lower BMI (body mass index), cholesterol, blood pressure, and rate of diabetes in the vegetarians than meat eaters, which are all established risk factors for heart disease,” says Tong.
Why More Research Is Needed on the Link Between Stroke and Diet
There are other reasons to approach the current study’s findings with caution.
The authors point out that this is a single observational study, so whether any of these diets definitively contributes to or reduces the risk for stroke or heart disease is yet to be determined.
Also, the study included mostly white European individuals, and results may not be applicable to other populations. In addition, dietary information from participants was self-reported, which may have skewed the results. Overall, the scientists suggest that more research is necessary in other populations.
“For appraising the overall health of nonmeat diets,” Tong says, “other outcomes beyond what is covered in the current study should also be considered.”
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