Eating avocados reduced the risk of heart attacks in both men and women, including when eaten in place of butter, cheese or processed meats, a new study found.

Cardiovascular disease is a leading killer worldwide, taking nearly 18 million lives every year, according to the World Health Organization. In the United States alone, the US Centers for Disease Control and Prevention says heart disease takes a life every 36 seconds.

Eating at least two servings of avocado a week reduced the risk of having a heart attack by 21% when compared to avoiding or rarely eating avocados. However, there was not an equivalent benefit in reducing the risk for stroke, according to the study published Wednesday in the Journal of the American Heart Association.

A serving of avocado, which is a fruit, was defined as "½ avocado or ½ cup of avocado, which roughly weighs 80 grams," said study author Lorena Pacheco, a postdoctoral research fellow in the department of nutrition at Harvard T.H. Chan School of Public Health in Boston.

"Although no one food is the solution to routinely eating a healthy diet, this study is evidence that avocados have possible health benefits," said Cheryl Anderson, chair of the American Heart Association's Council on Epidemiology and Prevention, in a statement. Anderson was not involved in the study.

"We desperately need strategies to improve intake of AHA-recommended healthy diets — such as the Mediterranean diet — that are rich in vegetables and fruits," said Anderson, who is also professor and dean of the Herbert Wertheim School of Public Health and Human Longevity Science at University of California San Diego.

Long-term study

The study followed more than 68,000 women and 41,000 men who were enrolled in two long-term government studies on risk factors for chronic disease: the Nurses' Health Study and Health Professionals Follow-up Study. All participants were free of cancer, coronary heart disease and stroke at the start of the studies and completed dietary questionnaires every four years over a 30-year period.

In addition to looking at the overall impact of eating avocados, researchers did statistical modeling and found consuming half a serving of avocado (¼ cup) a day instead of the same amount of eggs, yogurt, cheese, margarine, butter or processed meats (such as bacon) lowered the risk of heart attacks by 16% to 22%.

"The full benefit of routine avocado consumption observed here derives from swapping avocado into the diet, and less healthful foods out," said Dr. David Katz, a specialist in preventive and lifestyle medicine and nutrition, who was not involved in the study.

However, the study did not find a difference in risk reduction when a half-serving of avocado was replaced with an equivalent serving of nuts, olive and other plant oils. That makes sense, Katz said, because the health benefits are dependent on what food is replaced.

"If, for instance, the common swap were between avocado and walnuts or almonds, the health effects would likely be negligible since the foods have similar nutritional properties and expected health effects," said Katz, the president and founder of the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine.

But if the avocado replaced butter and margarine as a spread, or was eaten instead of processed meats or cheese on a sandwich, "the nutritional distinctions are sizable" and would be expected to change the health outcome, he added.

Although avocados are "particularly rich sources of monounsaturated fat, polyunsaturated fat and fiber," they can also be pricey and therefore not readily available to all, Katz said. Similar substitutes could include walnuts, almonds, olives, olive oil and a variety of seeds such as pumpkin and flax, he said.

Other foods to include that have major health benefit at "much lower price points," include beans, chickpeas and lentils, "and perhaps whole grains and related seeds like quinoa," Katz said.

Preventing heart disease

Preventing heart disease means keeping your weight, blood pressure and cholesterol under control, getting plenty of good-quality sleep and regular exercise, managing stress, limiting alcohol and avoiding tobacco use, and eating a healthy diet lower in sugar, processed foods and saturated fats, according to the National Library of Medicine.

The American Heart Association says your body needs fat to boost energy, protect organs, produce hormones and help with nutrient absorption. However, fats like monounsaturated and polyunsaturated fats are the heart-healthy choices. Olive oil, canola oil, peanut oil, safflower oil and sesame oil are sources of monounsaturated fats, along with avocados, peanut butter and many nuts and seeds.

Saturated fat and trans fats raise levels of LDL, known as "bad cholesterol," the AHA said. Saturated fats, such as butter, are typically solid at room temperature and are found in full-fat dairy products, eggs, coconut and palm oils, and fatty cuts of beef, pork and skin-on poultry.

Artificially made trans fats, also called partially hydrogenated oils, raise bad LDL cholesterol and lower good HDL cholesterol, which can increase the risk of heart disease, stroke and Type 2 diabetes. Those can often be found in "fried foods like doughnuts, and baked goods including cakes, pie crusts, biscuits, frozen pizza, cookies, crackers, stick margarines and other spreads," according to the AHA.