For most of the late twentieth century, dietary fat was the enemy. The logic seemed airtight: fat contains more than twice the calories per gram of carbohydrates or protein, fat is what accumulates in arteries before heart attacks, fat is what the body stores when you eat too much of it. The prescription was clear — eat less fat, live longer.

The evidence that undermined this consensus accumulated slowly over two decades and has still not fully penetrated mainstream dietary advice, even as nutritional scientists have largely abandoned the position. The critical insight was that fats are not a single category. Some fats — saturated fats from animal products and trans fats from industrial processing — do raise LDL cholesterol and appear to increase cardiovascular disease risk. Others, the monounsaturated and polyunsaturated fatty acids found in olive oil, avocados, nuts, and fatty fish, have the opposite effect: they raise HDL cholesterol, reduce inflammation, and are associated with lower rates of heart disease, diabetes, and certain cancers.

MUFAs — monounsaturated fatty acids — are the best-studied of the beneficial fats. The Mediterranean diet, which is unusually rich in MUFAs through olive oil and nuts, has been associated in multiple large studies with significant reductions in cardiovascular events and all-cause mortality. The populations that consume it, studied over decades in places like Crete and southern Italy, remain among the longest-lived in the world.

The practical implication is that the low-fat diet advice was not just unhelpful but probably harmful. When people reduced fat intake, they typically replaced those calories with refined carbohydrates — white bread, white rice, sugar — which have a worse metabolic profile than the fats they replaced. The obesity epidemic accelerated during the low-fat era.

Olive oil on your salad is not the enemy. It may, in fact, be part of the solution.