People who ate higher total amounts of red meat, processed red meat, and nondairy animal fat had an increased the risk of stroke, while those who ate more vegetable fat or polyunsaturated fat lowered it, according to a new 27-year study of more than 117,000 health professionals.
“Our findings indicate the type of fat and different food sources of fat are more important than the total amount of dietary fat in the prevention of cardiovascular disease including stroke,” said Fenglei Wang, PhD, lead author of the study and a postdoctoral fellow in the department of nutrition at Harvard’s T.H. Chan School of Public Health in Boston, in a press release.
Findings of the preliminary research are to be presented at the American Heart Association’s Scientific Sessions 2021, a fully virtual meeting held November 13 to 15, 2021.
Stroke Causes 1 in 20 Deaths in the United States
Stroke accounts for approximately 1 out of every 6 deaths from heart disease in the United States, according to the Centers for Disease Control and Prevention (CDC). When a stroke isn’t fatal, it can still cause lasting brain damage or long-term disability.
There are two types of stroke: An ischemic stroke is when something blocks blood supply to part of the brain, and a hemorrhagic stroke is when a blood vessel in the brain ruptures.
The Skinny on Fat
Fat is an essential part of any diet, and the body needs it for energy and to absorb vitamins, according to Mayo Clinic.
Saturated fat is found in high-fat meat; dairy products such as butter, lard, cheese, and yogurt; fried foods; and many baked goods. The American Heart Association (AHA) recommends that saturated fat account for 5 to 6 percent of a person’s daily calories.
RELATED: Good Fats vs. Bad Fats: Everything You Should Know About Fats and Heart Health
There are 2 types of unsaturated fat — monounsaturated fat and polyunsaturated fat. Monosaturated fat can be found in avocado, most nuts and nut butters, and vegetable oils such as olive, avocado, corn, or soybean oil, according to Mayo Clinic.
Polyunsaturated fats include omega-3 fats, which are found in fatty fish, such as salmon. They're also found in sunflower, corn, soybean, and cottonseed oils, pumpkin, sesame, and sunflower seeds, walnuts, and pine nuts.
Although some foods are better sources for certain fats, foods contain a combination of different types of fat, says Liz Weinandy, MPH, RDN, a registered dietitian-nutritionist at The Ohio State University Wexner Medical Center in Columbus. “Even though animal proteins have more saturated fats, they also have some polyunsaturated fats. Plants just typically have a lot more.”
Further Evidence That Some Types of Fat Are Beneficial for Health
The study is the first to comprehensively examine and compare how fat derived from vegetable, dairy, and nondairy animal sources affect stroke risk. The abstract was published on November 8, 2021, in the AHA journal Circulation.
RELATED: The Skinny on Fat: A Scientific Guide on the Best and Worst Sources
Researchers analyzed 27 years of follow-up from 117,136 participants in the Nurses’ Health Study (1984 to 2016) and Health Professionals Follow-Up Study (1986 to 2016). The average age of participants was 50 years old, 63 percent were women, 97 percent white, and all were free of heart disease and cancer at enrollment.
The amount and type of fat participants ate was measured via a food frequency questionnaire that was given at the beginning of the study and then every four years after that. Investigators used the self-reported information to estimate long-term dietary intake and then divided subjects into five groups, or quintiles, according to the amount of fat intake.
In the study, total red meat included beef, pork, or lamb, as a main dish, in sandwiches, or in mixed dishes, and processed red meats. Processed red meats included bacon, sausage, bologna, hot dogs, salami, and other processed meats.
Over the course of the study, there were 6,189 stroke events.
Key findings of the study included:
- Participants who ate the most animal fat (from nondairy sources) were 16 percent more likely to experience a stroke than those who ate the least.
- People who ate the highest amount of vegetable fat and polyunsaturated fat had a 12 percent reduced stroke risk compared with those who ate the lowest amounts of those types of fat.
- Participants who ate one more serving of total red meat every day had an 8 percent higher risk of stroke, and those consuming one more serving of processed red meat had a 12 percent higher risk of stroke.
- Eating dairy fat from sources such as cheese, butter, milk, ice cream, and cream was not associated with a higher risk of stroke.
Based on the findings, researchers recommend that people reduce their risk of stroke by eating less red and processed meat, trim fat from meat when they do consume it, and cook with nontropical vegetable oils rather than lard or beef fat.
Most of these findings are consistent with findings from other observational studies throughout the years and add further evidence to support the recommendations already in place to substitute healthier vegetable fats for less healthy animal ones, says Weinandy.
“It has been well observed that certain fats can increase or decrease the risk for heart disease. For example, it appears most fat that comes from animals — with the exception of fish — may increase LDL, the bad cholesterol. We know when people replace animal fat with healthier vegetable versions, like olive oil, sunflower, or safflower, they can usually lower their LDL cholesterol,” says Weinandy.
Findings Limited by Self-Reported Data and Lack of Diversity
This study was observational, and so it’s important not to assume a cause and effect relationship because there may be many other factors that could influence stroke risk, she says.
An observational study is one that studies a certain outcome in participants without any type of intervention. “For example, maybe the participants that exercised more were the ones who didn’t have strokes. In other words, there can be other factors in disease risk,” says Weinandy.
The authors acknowledge other limitations of the study. The dietary information was self-reported and relied on people remembering what they ate, which can lead to inaccuracies.
The participants were almost all white, and the findings may not apply to people of different racial or ethnic backgrounds. Race plays a large role in stroke risk — the risk of having a first stroke is almost twice as high for black Americans as for white Americans, and black Americans have the highest rate of death due to stroke, per the CDC.
More Research Is Needed to Explore Dairy Fat’s Impact on Stroke Risk
Even though fat from dairy wasn’t associated with stroke risk in this study, more research is needed to confirm this finding, says Maya Vadiveloo, PhD, RD, assistant professor and researcher at the University of Rhode Island in Kingston, and a coauthor of the AHA’s recent dietary guidelines. “We don’t have adequate evidence from larger randomized controlled trials, especially ones that follow people for longer period of time to really be able to say that dairy doesn’t have the same adverse effects,” she says.
To Improve Heart Health, Focus on a Healthy Dietary Pattern
Rather than avoiding or seeking out certain foods or ingredients, Dr. Vadiveloo recommends that people focus on adopting a healthy eating pattern that focuses on eating more plant-based proteins, whole grains, fruits, and vegetables, while limiting intake of highly processed foods.
Take all the ingredients into account when considering if a food is a healthy choice or not, she suggests. For example, a store-bought baked good, such as a muffin, may be made with canola oil or another vegetable oil that would be recommended for heart health — but that doesn’t mean it’s healthy.
“The issue would be that in many cases, the muffin would be high in refined grains and sugar, so it doesn’t broadly meet dietary guidelines,” says Vadiveloo. Foods with refined grains and sugar can also contain dietary sodium, which is a major contributor to stroke, she adds.
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