The official advice to eat less fat to avoid dying of heart disease isn't backed up by the long-term studies of large groups of people.

The studies used in this review mostly involved men, so we can't be sure the results apply to everyone, like women or different ethnic groups.

Some big studies that looked at lots of people who ate less saturated fat didn’t find that they lived longer or had fewer heart attacks, which makes people question why we’ve been told to avoid foods like butter and cheese for so long.

For people who haven't had a heart attack yet, how much fat they eat doesn't seem to affect their chance of dying from heart disease, according to combined data from several long-term studies.

Eating less saturated fat—like butter or fatty meats—doesn’t seem to lower the risk of dying from heart problems or other causes, even after years of doing it, according to a review of nine big studies.

There isn’t strong enough proof to say that eating less saturated fat and more vegetable oils will definitely prevent heart disease, according to this big review.