After being vilified for years, fat is having a comeback. But with so many sources and types of fat out there, it can be hard to keep track of what’s healthy and what’s not.

A new study, however, offers a simple rule of thumb: Plant fat sources appear to be better for you than animal sources, at least when it comes to monounsaturated fats.

The research, which was presented Wednesday at an American Heart Association conference in New Orleans, found that plant-based monounsaturated fats — like those found in vegetable oils, avocados, nuts and seeds — are associated with a lower risk of dying from heart disease and other causes. Animal-based monounsaturated fats — like those in meat, dairy and eggs — are associated with a higher risk, according to the research.

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“We have observed a beneficial role of monounsaturated fats for the prevention of cardiovascular and total mortality when plant-based foods are the primary sources,” says Marta Guasch-Ferre, a research associate in the department of nutrition at the Harvard T.H. Chan School of Public Health, who co-authored the paper with Dr. Geng Zong and Dr. Qi Sun.

Though the researchers could not prove cause-and-effect, they looked for patterns in the dietary data of almost 100,000 people. They followed the people for about 22 years, and people completed food questionnaires every four years. During those decades of follow-up, more than 20,600 people died, roughly 4,500 from heart disease.

People who ate lots of plant fats had a 16% lower risk of dying compared to those with lower intakes, while those who ate lots of animal fats had a 21% higher risk, compared to those who didn’t eat many of these foods. Replacing even a relatively small number of calories from trans fats, saturated fats and refined carbohydrates with an equal number from plant fats also seemed to cut a person’s risk of dying by 10 to 15%, the researchers found.

The difference between plant versus animal fat sources, Guasch-Ferre says, is likely due to the other nutrients found in those foods. Plant sources of monounsaturated fats are typically also rich in vitamins, polyphenols and polyunsaturated fats — longer-chain fats which are known to be heart-healthy. Sources of animal fats, on the other hand, tend to contain lots of saturated fat and cholesterol, which can contribute to heart disease.

“Recently, dietary recommendations have shifted toward diets including higher quantities of plant-based foods over animal-based foods,” Guasch-Ferre wrote. “Our results are in accordance with these recommendations.”

Write to Jamie Ducharme at jamie.ducharme@time.com.