Dong Wang of Harvard Medical School and colleagues conducted a prospective cohort study and found that a diet high in butter was associated with increased mortality, while a diet high in vegetable oil was associated with decreased mortality. The analysis included 221,054 adult participants in the prospective Nurses' Health Study (1990–2023; mean age at enrollment 56.1 years), Nurses' Health Study II (1991–2023; 36.1 years), and Health Professionals Follow-up Study (1990–2023; 56.3 years). At baseline, they did not suffer from cancer, cardiovascular disease, neurodegenerative diseases, or diabetes. Diet was analyzed using a semiquantitative questionnaire every four years; butter and vegetable oil consumption were assessed by quartiles. Follow-up continued for up to 33 years. The results were published in the journal JAMA Internal Medicine.
During the follow-up period, 50,932 participants died, including 12,241 from cancer and 11,240 from cardiovascular disease. Confounding estimates showed that the highest butter consumption was associated with a 15 percent increase in mortality compared to the lowest, while the highest vegetable oil consumption was associated with a 16 percent decrease compared to the lowest (this association was most significant for canola, olive, and soybean oils). The researchers also calculated that replacing 10 grams of butter per day with an equivalent amount of vegetable oil was associated with a 17 percent reduction in overall mortality and a 17 percent reduction in cancer mortality in particular. For all parameters, p < 0.001.
