A study published in JAMA Internal Medicine suggests that a higher intake of butter is associated with increased mortality while a higher intake of plant-based oils is associated with reduced mortality [1].
Fats: the good, the bad, and the ugly
Previous research has found that not all dietary fats are created equal. Results of different studies encourage the consumption of unsaturated fats, the avoidance of saturated fats, and the elimination of trans fats from the diet [2].
However, in real life, people do not consume fats in isolation. Instead, each food item contains a mix of fats. Therefore, the researchers in this study focused not on fat categories but on two dietary items: butter and plant-based oils. While both are a mix of fats, the former is rich in saturated fats, while the latter contains mainly unsaturated fats.
Given its predominant composition, it’s easy to assume that butter would be the ‘bad guy’ in this duo. Some older research supports this, linking butter to increased cardiovascular risk [3]; however, recent studies have shown mixed results regarding the relationship between butter consumption and mortality [4-8].
On the other hand, studies and clinical trials have linked unsaturated fat-rich plant-based oils to improved lipid profiles, reduced inflammation [9], and lower risks of cancer, cardiovascular disease, and type 2 diabetes [10-13]. However, those studies mainly focus on olive oil, and other oil types are not given enough attention.
Broad databases for comparison
Given the gaps and conflicting results in previous research, the researchers of this study investigated the associations between butter and plant-based oils intake and the risk of total and cause-specific mortality among adults in the United States.
The researchers used the data from three large cohorts: the Nurses’ Health Study, the Nurses’ Health Study II, and the Health Professionals Follow-up Study. In total, those studies included 221,054 adults followed up for up to 33 years.
The researchers assessed the intake of butter and plant-based oils (safflower, soybean, corn, canola, and olive oil) based on the food frequency questionnaires that study participants completed every 4 years.
Bread and butter, or maybe not?
The researchers analyzed all three cohorts, adjusting for potential confounders, and concluded that participants who consumed the highest volumes of butter, compared to those who consumed the least, had a 15% higher risk of total mortality.
This study differentiated between the uses of butter. They reported no association between mortality and the use of butter for baking and frying, which is likely because the amounts are relatively small and unlikely to have any significant effect. However, among participants who added butter to their food or bread, a 4% increase in total mortality was observed for every 5g of butter consumed daily.
Not all oils are created equal
On the other hand, people who who consumed the most plant-based oils, compared to those who consumed the least, showed 16% lower mortality rates. When olive oil was removed from the plant-based oil group, an 8% reduction in mortality remained.
This category encompasses a wide range of oils, and the researchers discovered differences between them. They observed a significant association between higher consumption of canola oil, soybean oil, and olive oil and lower total mortality; however, no associations were found for corn and safflower oil consumption and mortality.
The authors propose several explanations for the lack of association between corn oil consumption and mortality. Corn oil contains small amounts of omega-3 fatty acids, which can potentially be oxidized during frying, producing harmful byproducts. Some studies also suggest the presence of trans fats in corn oil. The authors caution against drawing firm conclusions about this piece of data due to the low consumption of corn oil and safflower oil, which makes the analysis less reliable.
The results regarding plant-based oils and butter associations with mortality, in general, were consistent across different subgroups of participants divided by age, BMI, and lifestyle factors.
Cause-specific mortality
Mortality is a very general term, and the causes of death for each individual can be different. Therefore, the researchers also examined the association between butter and plant-based oil consumption and cause-specific mortality, focusing on cancer and cardiovascular diseases.
These results were similar to those for all-cause mortality, with plant-based oils being associated with reduced mortality for cancer-related mortality and cardiovascular diseases: 11% and 6%, respectively, per 10-gram increase in daily consumption. In contrast, butter was associated with an increased risk of cancer mortality but not cardiovascular disease mortality.
The researchers discuss a possible mechanism linking butter intake and cancer mortality. They link the high saturated fat levels in butter to adipose tissue inflammation, which is one of the pathways in cancer development. Additionally, dietary saturated fats impact hormonal activity, which, in turn, can affect the development of hormone-sensitive cancers such as breast and prostate cancer.
Looking into specific oils, the researchers showed an inverse association between the increased consumption of olive oil, canola oil, and soybean oil and cancer mortality. Higher consumption of olive oil was also inversely associated with mortality from cardiovascular disease.
The positive impact of olive oil is not surprising, as it has been repeatedly shown to have beneficial effects on cardiovascular health. Previous studies have also shown that including polyunsaturated fat-rich soybean oils in the diet offers several benefits, including lower circulating cholesterol levels and a reduced risk of coronary heart disease and total mortality [14, 15]. However, in this study, the researchers did not find a significant association between soybean oil and reduced cardiovascular mortality. Therefore, further investigation is needed to untangle those two observations.
Making better dietary choices
A substitution analysis sheds some light on how substituting butter in the diet with plant-based oils might be of benefit. This analysis found that substituting 10 grams of butter consumption per day with the equivalent amount of plant-based oils is associated with a 17% reduction of total mortality and cancer mortality. For cardiovascular mortality, the researchers observed a 6% reduction, but this result was not statistically significant.
Small change, big difference
This research provides additional evidence supporting the reduction of saturated fatty acids in the diet and substituting them with unsaturated fatty acids, as recommended by the American Heart Association’s dietary guidelines and the Dietary Guidelines for Americans.
This study suggests that even such a small change as “replacing 3 small pats of butter (approximately 15 g) with 1 tablespoon of plant-based oil (approximately 15 g) in the daily diet could contribute to lowering the risk of premature mortality.”
Literature
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