Fat in the diet has long been linked to stroke risk, but new research presented Monday suggests that the type of fat, not the amount, may be the most important factor.
The study found that eating more animal fat was associated with a higher risk of stroke, while getting more fat from plant sources was associated with a lower risk.
Stroke is the fifth leading cause of death in the United States, and nutritionists have long worked to understand how a person's diet plays a role.
"If everyone could make small adjustments, such as reducing red and processed meat intake, the public health implications will be huge," said study leader Fenglei Wang, a postdoctoral researcher at Harvard T.H. Chan School of Public Health. Wang's findings were presented Monday at the American Heart Association Scientific Sessions 2021 and have not yet been published in a peer-reviewed journal.
The results come from 27 years of data from more than 117,000 healthcare professionals. The data comes from two of the largest and longest-running nutrition studies in the US: the Nurses' Health Study and the Health Professionals Follow-up Study. In those studies, participants regularly filled out questionnaires about their diet and provided researchers with medical records. (One of the limitations of the study is that the participants in the two long-term studies are predominantly white health professionals.)
A stroke occurs when blood flow to part of that brain is cut off. It can be caused by a blood clot, called an ischemic stroke, or the rupture of a blood vessel, called a hemorrhagic stroke. Ischemic strokes account for nearly 90 percent of strokes each year, while hemorrhagic strokes account for 10 percent.
The study found that a higher intake of vegetable fats was linked with a lower risk of ischemic stroke, with those who ate the most vegetable and polyunsaturated fats (such as olive oil) were 12 percent less likely to have an ischemic stroke compared to those who ate the most vegetable and polyunsaturated fats (such as olive oil). ate the least of such vegetable fats. Eating less animal fats was also found to have a positive effect on the risk of types of stroke. Participants who ate the highest amounts of animal fat — including fat from red and processed meat, but excluding dairy fat — were 16 percent more likely to have a stroke than those who ate the least amount of animal fat. In contrast, dairy fat was not associated with stroke risk.
"This study fits with the previous nutritional science showing that we should eat a plant-based diet in the first place," says Dr. Michael Miedema, director of cardiovascular prevention at the Minneapolis Heart Institute, who was not involved in the new research. "The average American diet is based on animal protein, and the sooner we can shift that to more plant-based, the better off we'll be."
But how healthy a person's diet becomes "usually depends on what you replace meat with," he said.
Tracy Severson, a registered dietitian at the Oregon Health & Science University Knight Cardiovascular Institute, emphasized the importance of choosing whole foods as sources of vegetarian protein, such as lentils and beans, rather than processed options such as plant-based meats, which usually have a lot of salt, sugar and saturated fats.
She said the findings don't mean everyone should cut out meat from their diet completely.
"I don't think anyone needs to look at this and go vegan if that's not what they want to do, but swapping even one meal of red meat a week and replacing it with a raw vegetarian option will be good for cardiovascular health," she said. .
Previous research has produced mixed conclusions about the effect of tropical vegetable oils such as palm oil and coconut oil on cardiovascular health. The study authors recommended swapping animal fats such as lard or tallow for non-tropical vegetable oils, including olive oil, corn oil or soybean oil. Oils labeled as refined are considered processed.
"Patients often ask for ingredients or nutrients and are looking for a certain amount, and my answer is always that the vast majority of groceries you buy shouldn't have an ingredient list," Miedema said. “If you buy fruits and vegetables and olive oil and fish, you're probably doing it right. If you're eating packaged foods or going through the drive-thru, you're probably in trouble.
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