A study following 90,000 people over 28 years found that replacing about 10 grams of butter per day with olive oil is associated with a 15 to 19% decrease in the risk of cardiovascular and cancer mortality. A second study from 2025, conducted on more than 221,000 adults over up to 33 years, confirms a decrease in mortality of about 17% by substituting butter with vegetable oils. These findings are explained by the nature of the fats: butter contains harmful saturated fats for the arteries, while olive oil provides beneficial unsaturated fats for the cardiovascular system. Following 90,000 people over three decades is not a survey hastily conducted between two doors. It is the kind of meticulous work that allows one to see the emergence of heavy trends, far from the effects of food fads. These two large American cohorts, composed of adults without cardiovascular disease or cancer at the start, were observed for approximately twenty-eight years. Enough time to see who, among the heavy consumers of butter and the advocates of olive oil, fared better in the long run. And the results were not isolated: another cohort study, published in 2025, followed more than 221,000 adults for up to thirty-three years, with conclusions in the same direction. In other words, it is not a statistical coincidence. Replacing about 10 grams per day of butter, margarine, mayonnaise or dairy fats with an equivalent amount of olive oil is associated with a lower risk of mortality. Specifically, a higher consumption of olive oil was linked to a 19% reduced risk of mortality from cardiovascular disease, and 17% for cancer mortality. The same goes for the 2025 study: the simple daily and modest replacement of butter with vegetable oils was associated with lower mortality, around 17%. And good news for those less fond of olive oil: it is not necessary to consume liters: consuming at least half a tablespoon per day would already be enough to observe a decrease in cardiovascular risk. Butter is rich in saturated fats, those that tend to promote bad cholesterol and gradually clog the arteries. Olive oil, on the other hand, is mainly composed of unsaturated fats, which are gentler on the cardiovascular system. Therefore, it is not the amount of fat consumed that makes all the difference, but its chemical composition. This reminder echoes the famous Mediterranean diet, of which olive oil is one of the pillars, and which had already shown, in a widely cited trial, about 30% fewer major cardiovascular events among those who adopted it. In practice, what does this mean for kitchen cabinets? There is no need to completely ban butter, nor to feel guilty about each Sunday croissant. The idea, more subtle, is to make targeted and sustainable substitutions rather than a complete deprivation: Replace part of the cooking butter with olive oil, especially for pan-frying and slow-cooked dishes. Prefer olive oil for vinaigrettes and morning spreads. Keep butter for uses where it is irreplaceable, in measured quantities, such as certain pastries. In short, it is not about reinventing one's cuisine overnight, but adjusting the proportions gradually. A drizzle of olive oil instead of a nut of butter, here or there, and it is already a first step toward arteries that may thank you later. It remains to be seen whether butter, so deeply rooted in French habits, will be willing to give up some ground without too much resistance.