Is butter bad for you?

Butter is having a mo. In 2024 American usance per somebody come to its highest in almost 60 years. Long-standing fears nearly fat’s impact on heart health seem to be dissipating: today, fat is in and it is carbohydrates, sugars and processed foods that are out. But a new scientific study reports that butter-eating is associated with an early death. So: is butter really bad for you?

Reaching an answer involves understanding that not all fats are alike. At a chemical level, fats are chains of carbon atoms; some are saturated—meaning every carbon atom clings to two hydrogen atoms—while others are unsaturated—meaning some carbon atoms bond to only one of hydrogen. Those structural differences can dramatically affect how those fats interact with the body. Saturated fats, for example, raise levels of cholesterol, a fatty molecule that gathers in arteries and can contribute to cardiovascular disease. They do this, in part, by partially disabling receptors in the liver which cause excess cholesterol to be extracted from the bloodstream and dumped into bile. Unsaturated fats, by contrast, actively reduce the levels of cholesterol by activating these same liver receptors.

Most of the fat in butter is of the saturated variety. It therefore stands to reason that butter should have a negative effect on heart health. Indeed, there is good evidence from randomised-controlled studies that replacing butter with plant-based oil can reduce cholesterol.

There is more bad news for butter-lovers. The new study, published on March 6th in JAMA Internal Medicine by authors in Massachusetts and Denmark, relied on data from three long-run trials of American medical professionals. For almost 33 years 220,000 nurses and doctors have been regularly surveyed about their lifestyle, diet and health. Many have died in this time. The authors found that, after controlling for other aspects of demographics, diet and lifestyle, those people who ate the most butter (averaging around one tablespoon per day) had a 15% increased risk of mortality compared with those who avoided the stuff. By contrast, people who consumed the most plant-based oils, such as canola, soyabean or olive oil—all of which have low levels of saturated fat—had a 16% lower mortality rate than those who consumed the least.

And, though the study could not show that butter increased the risk of dying from cardiovascular diseases, consuming more plant-based oils did lower that particular risk. Butter-eating was, instead, linked to more deaths from cancer. The authors found that replacing ten grams of butter daily with the same amount of plant-based oil appeared to reduce the cancer mortality risk by 17%.

Observational studies like this one are rarely cut and dried, however. George Davey Smith, an epidemiologist at the University of Bristol, points out that there are other differences in health-related behaviours between the groups: the voracious butter-eaters contained twice as many smokers, for example, as the butter-avoiders. He argues it is not possible to fully control for such differences, which means some non-dietary factors could be at play.

If you do bin your butter, choose your alternatives wisely. Margarine has less saturated fat than butter (and modern varieties tend to be free of hydrogenated or trans-fats, which also negatively affect cholesterol levels), but it has been linked to higher levels of type-2 diabetes. If you want a sure swap, though, olive oil is probably your best bet.

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