A large-scale study found that replacing butter with plant-based oils, such as soybean and olive oil, can significantly lower the risk of death from all causes. Researchers linked higher butter intake to a 15% increased risk of mortality, while higher plant-based oil intake was associated with a 16% lower risk. Substituting 10 grams of butter daily with plant-based oil could reduce mortality by 17%.

The study, which tracked the dietary habits of over 200,000 individuals for three decades, found that diets rich in butter but low in plant oils were linked to an increased risk of mortality.

A new study conducted by researchers from Mass General Brigham, the Harvard T.H. Chan School of Public Health, and the Broad Institute of MIT and Harvard suggests that replacing butter with plant-based oils may offer significant health benefits, including a reduced risk of premature death.

Analyzing dietary and health data from 200,000 individuals over more than 30 years, the researchers found that higher consumption of plant-based oils—particularly soybean, canola, and olive oil—was linked to lower overall mortality, as well as reduced deaths from cancer and cardiovascular disease. In contrast, butter consumption was associated with an increased risk of both total mortality and cancer-related deaths.

The findings were published in JAMA Internal Medicine and were also presented at the American Heart Association’s EPI/Lifestyle Scientific Sessions.

Significant Health Impact of Swapping Butter for Oil

“What’s surprising is the magnitude of the association that we found — we saw a 17% lower risk of death when we modeled swapping butter with plant-based oils in daily diet. That is a pretty huge effect on health,” said study lead author Yu Zhang, MBBS, research assistant at the Channing Division of Network Medicine at Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system. Zhang is also a student in the Department of Epidemiology at Harvard Chan School.

A key difference between butter and oil is the types of fatty acids contained in them. Butter is rich in saturated fatty acids, while plant-based oils have more unsaturated fatty acids. While there have been many studies on dietary fatty acids, fewer studies have focused on their primary food sources, including butter and oils. Many previous studies have looked at a person’s diet at a point in time and have been done in a small population, limiting their applicability to public health.

The new study analyzed dietary data from 221,054 participants in the Nurses’ Health Study (NHS), Nurses’ Health Study II (NHSII), and Health Professional Follow-up Study (HPFS). Every four years, they answered questions about how often they consumed certain types of food. The researchers used the data to estimate how much butter and plant oils they ate.

Total butter intake included butter from butter and margarine blend, spreadable butter added to food and bread, and butter used in baking and frying at home. The intake of plant-based oils was estimated based on the reported use in frying, sautéing, baking, and salad dressing.

The researchers also identified participants who had died and their causes of death. Using statistics to compare death rates across different diet intake levels, the researchers found that participants who ate the most butter had a 15% higher risk of dying than those who ate the least. In contrast, those who ate the most plant-based oils had a 16% lower risk of death than those who ate the least.

The Benefits of a Simple Dietary Change

“People might want to consider that a simple dietary swap — replacing butter with soybean or olive oil — can lead to significant long-term health benefits,” said corresponding author Daniel Wang, MD, ScD, of the Channing Division of Network Medicine at Brigham and Women’s Hospital. Wang is also an assistant professor in the Department of Nutrition at Harvard Chan School and an associate member at the Broad Institute of MIT and Harvard. “From a public health perspective, this is a substantial number of deaths from cancer or from other chronic diseases that could be prevented.”

The researchers also did a substitution analysis, which mimics how swapping butter for plant oils would impact health in a feeding trial. They found that substituting 10 grams of butter a day (less than a tablespoon) with equivalent calories of plant-based oils could lower cancer deaths and overall mortality by 17%.

“Even cutting back butter a little and incorporating more plant-based oils into your daily diet can have meaningful long-term health benefits,” Wang said.

One limitation of the study is that the participants are mainly health professionals, so they might not represent the U.S. population as a whole, the researchers said. In the future, they’d like to study the biological mechanisms underlying why this dietary change has such a large impact.