In a detailed and powerful examination of how dietary fat affects health, researchers from Harvard T.H. Chan School of Public Health have shown that consuming higher amounts of unsaturated fats is associated with lower mortality. The findings suggest that replacing saturated fats like butter, lard and fat in red meat with unsaturated fats from plant-based foods—like olive oil, canola oil and soybean oil—can confer substantial health benefits and should continue to be a key message in dietary recommendations.

Published in the July 5 issue of JAMA Internal Medicine, this large-scale study followed 126,233 participants from two long-term studies—the Nurses’ Health Study and the Health Professionals Follow-Up Study—who answered survey questions every 2-4 years about their diet, lifestyle and health for up to 32 years.

Different types of dietary fat had different associations with mortality, the researchers found. Trans fats—which are near being phased out of food–had the most significant adverse impact on health. Every 2% increase in trans fat intake was associated with a 16% higher chance of premature death during the study period. Higher consumption of saturated fats was also linked with greater mortality risk. When compared with the same number of calories from carbohydrate, every 5% increase in saturated fat intake was associated with an 8% higher risk of overall mortality.

Conversely, consuming higher intakes of unsaturated fats—both polyunsaturated and monounsaturated—was associated with 11%-19% lower overall mortality than getting the same number of calories from carbohydrates. Among the polyunsaturated fats, both omega-6 fatty acids (found in most plant oils) and omega-3s (found in fish, soy, and canola oil) were associated with lower risk of premature death.

“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 with a variety of liquid vegetable oils,” said senior author Frank Hu, MD, PhD, MPH, professor of nutrition and epidemiology at Harvard Chan School and professor of medicine at Harvard Medical School.