Butter vs. Plant Oils: Impact on Mortality

Not such good news for butter lovers: a recent Harvard study in JAMA Internal Medicine drew on decades of long-term observational data to investigate how butter and plant oils affect mortality. The basic takeaway? “A higher intake of butter increases mortality risk, while a higher intake of plant-based oil will lower it,” says Yu Zhang, lead author of the study. Importantly, substituting certain plant oils for butter may help people live longer.

Study Overview

Researchers used dietary questionnaires from more than 221,000 adults in the Nurses’ Health Study, Nurses’ Health Study II, and Health Professionals Follow-Up Study, tracking their deaths over up to 33 years. Participants were divided into four groups based on reported butter and plant-oil intake. The highest consumers were compared with the lowest consumers to assess risk.

Key Findings

  • Those eating the most butter had a 15% higher risk of death versus those eating the least.
  • Those consuming the most plant oils had a 16% lower risk of death versus those consuming the least.
  • Higher butter intake increased risk for cancer deaths.
  • Higher plant-oil intake reduced risk of dying from cancer or cardiovascular disease (stroke or heart attack).

Which Plant Oils Are Beneficial?

Of the five plant oils studied, only soybean, canola, and olive oil were linked with survival benefits.

Effects of Substituting Butter

Modeling showed that swapping just 10 grams of butter per day (slightly less than a tablespoon) for an equivalent amount of soybean, canola, or olive oil was associated with fewer total deaths and fewer cancer deaths.

According to Dr. Walter C. Willett of Harvard, “Butter has almost no essential fatty acids and a modest amount of trans fat—the worst type of fat for cardiovascular disease.” By contrast, plant oils are rich in antioxidants, essential fatty acids, and unsaturated fats, which support healthier cholesterol and triglyceride levels, lower insulin resistance, and may reduce chronic inflammation.

Recommendations

  • Use liquid plant oils instead of butter for cooking and at the table whenever possible.
  • Sample a variety of oils—different olive oils, mustard oil, sesame oil—to find flavors you enjoy.
  • For flavor, a small amount of butter occasionally is acceptable, or blend butter with oils.

These suggestions align with American Heart Association recommendations and the Dietary Guidelines for Americans for lowering chronic disease risk.

Study Strengths and Limitations

  • Large sample size and up to 33 years of follow-up.
  • Adjustments for age, physical activity, smoking status, and family history of cancer and diabetes.
  • Observational design cannot prove cause and effect, only associations.
  • Most participants were white health-care professionals, so findings may not generalize to all populations.