Butter and Plant-Based Oils Intake and Mortality

The relationship between butter and plant-based oil intakes and mortality remains unclear, with conflicting results from previous studies. Long-term dietary assessments are needed to clarify these associations. To investigate associations of butter and plant-based oil intakes with risk of total and cause-specific mortality among US adults. This prospective population-based cohort study used data from 3 large cohorts: the Nurses' Health Study (1990-2023), the Nurses' Health Study II (1991-2023), and the Health Professionals Follow-up Study (1990-2023). Women and men who were free of cancer, cardiovascular disease (CVD), diabetes, or neurodegenerative disease at baseline were included. Primary exposures included intakes of butter (butter added at the table and from cooking) and plant-based oil (safflower, soybean, corn, canola, and olive oil). Diet was assessed by validated semiquantitative food frequency questionnaires every 4 years. Total mortality was the primary outcome, and mortality due to cancer and CVD were secondary outcomes. Deaths were identified through the National Death Index and other sources. A physician classified the cause of death based on death certificates and medical records. During up to 33 years of follow-up among 221 054 adults (mean [SD] age at baseline: 56.1 [7.1] years for Nurses' Health Study, 36.1 [4.7] years for Nurses' Health Study II, and 56.3 [9.3] years for Health Professionals Follow-up Study), 50 932 deaths were documented, with 12 241 due to cancer and 11 240 due to CVD. Participants were categorized into quartiles based on their butter or plant-based oil intake. After adjusting for potential confounders, the highest butter intake was associated with a 15% higher risk of total mortality compared to the lowest intake (hazard ratio [HR], 1.15; 95% CI, 1.08-1.22; P for trend < .001). In contrast, the highest intake of total plant-based oils compared to the lowest intake was associated with a 16% lower total mortality (HR, 0.84; 95% CI, 0.79-0.90; P for trend < .001). There was a statistically significant association between higher intakes of canola, soybean, and olive oils and lower total mortality, with HRs per 5-g/d increment of 0.85 (95% CI, 0.78-0.92), 0.94 (95% CI, 0.91-0.96), and 0.92 (95% CI, 0.91-0.94), respectively (all P for trend < .001). Every 10-g/d increment in plant-based oils intake was associated with an 11% lower risk of cancer mortality (HR, 0.89; 95% CI, 0.85-0.94; P for trend < .001) and a 6% lower risk of CVD mortality (HR, 0.94; 95% CI, 0.89-0.99; P for trend = .03), whereas a higher intake of butter was associated with higher cancer mortality (HR, 1.12; 95% CI, 1.04-1.20; P for trend < .001). Substituting 10-g/d intake of total butter with an equivalent amount of total plant-based oils was associated with an estimated 17% reduction in total mortality (HR, 0.83; 95% CI, 0.79-0.86; P < .001) and a 17% reduction in cancer mortality (HR, 0.83; 95% CI, 0.76-0.90; P < .001). In this cohort study, higher intake of butter was associated with increased mortality, while higher plant-based oils intake was associated with lower mortality. Substituting butter with plant-based oils may confer substantial benefits for preventing premature deaths.