Cholesterol, a fatty substance mostly made by the liver and used by the body to build cells and produce hormones, has become a heart-health bogeyman. There are several types, but high levels of LDL (low-density lipoprotein) cholesterol increase the risk of heart attack and stroke. Often labelled “bad” cholesterol, LDL builds up over time on artery walls, narrowing them and restricting blood flow.

High LDL cholesterol is not confined to people who are overweight. “Genetics are the main driver of higher LDL cholesterol levels,” says Naveed Sattar, professor of cardiometabolic medicine at the University of Glasgow. “Diets have smaller effects and it’s not necessarily the total calories that count; it’s the amount of saturated fat.” (Found in cakes, biscuits, chocolate and many ultra-processed foods, saturated fat can raise LDL levels.) All of this means someone relatively lean can still have high cholesterol, either because of their genetic profile or dietary pattern.

“Obesity per se has minimal effect on LDL cholesterol levels,” says Sattar. “But it affects other blood lipids [types of fatty substances, including cholesterol] much more.” In particular, excess body fat is linked to higher levels of triglycerides and remnant cholesterol, both of which increase the risk of cardiovascular disease. Obesity is also closely tied to conditions such as type 2 diabetes and high blood pressure, which can also make LDL more harmful.

Worried about cholesterol? From the age of 40, people in the UK are eligible for an NHS health check, which includes a cholesterol test. “Your GP can easily assess your overall cardiovascular risk,” says Sattar. “Because it’s not just about LDL – factors such as diabetes, weight and blood pressure all play a part.” Before then, it’s worth finding out if you have a family history of early heart disease.