To combat body fat and live a longer, healthier life, you have to eat fat—the right kind that is. It’s actually quite simple, and new research out of Harvard is piling on the reasons why you should reacquaint yourself with fatty foods: Replacing five percent of your caloric intake from so-called bad fats (like trans and saturated fat found in red meat and lard) with unsaturated fat from plant-based foods (like olive oil) can reduce your risk of death by 27 percent. Twenty-seven percent! 

The science

In the study, published in JAMA Internal Medicine, researchers compiled information from 126,233 participants from two very large long-term studies. Participants answered surveys every 2-4 years about their everyday diet, lifestyle, and health for up to 32 years. During the followup, 33,304 deaths were documented. While a bit morbid, the researchers were able to examine the relationship between dietary fat and overall death, as well as deaths due to cancer, cardiovascular, neurodegenerative, and respiratory disease. 

Trans fats—which are being phased out of most foods thanks to the FDA—had the worst adverse impact on health. For every 2 percent higher intake of trans fat, there was a 16 percent higher chance of premature death. The same trend was seen with a greater consumption of saturated fats and mortality risk: When compared with the same number of calories from carbohydrates, every 5 percent increase in saturated fat consumption was linked with an 8 percent higher risk of overall mortality.

Meanwhile, higher intakes of unsaturated—polyunsaturated and monounsaturated—good fats was associated with an 11 percent and 19 percent lower risk of death respectively compared with the same number of calories from carbohydrates. Specifically, it’s the omega-6, found in most plant oils, and omega-3 fatty acids, found in fish and soy and canola oils, natural to polyunsaturated fats that keeps you healthy and wards off death.

How to replace bad fat with good fat

The health benefits of certain types of fats were largely dependent upon what people were replacing them with, the researchers say. People who replaced bad saturated fats with good unsaturated fats—especially polyunsaturated fats—had a significantly lower risk of death overall, as well as a lower risk of death from CVD, cancer, neurodegenerative disease, and respiratory disease, compared with those who maintained high intakes of saturated fats. 

Interestingly, kicking out both good and bad fats didn't have as great of an effect. The researchers found when people replaced saturated fats with carbs (instead of good fats), they had only a slightly lower mortality risk. What’s more, replacing total fat with carbs altogether actually caused slightly higher instances of death. 

It’s likely because carbs in the American diet tend to be primarily refined starch and sugar, which have a similar influence on mortality risk as saturated fats. (Read our dossier on the 13 best sources of whole grains.)

"Our study shows the importance of eliminating trans fat and replacing saturated fat with unsaturated fats, including both omega-6 and omega-3 polyunsaturated fatty acids. In practice, this can be achieved by replacing animal fats like red meat with a variety of liquid vegetable oils," senior study author Frank Hu said in a press release

Check out the best sources of plant-based, and some incredibly healthy animal-based, fats.