Cholesterol is a fatty molecule in the blood and, generally speaking, having too much is bad: it can stick to the walls of your arteries and increase the risk of heart disease. Most foods, with the exception of offal, eggs and shellfish, don’t contain any cholesterol, but many contain saturated fats, which are turned into cholesterol by the liver. However, cholesterol itself isn’t unhealthy – in fact, you wouldn’t be able to live without it. The body uses cholesterol as a kind of padding, coating the outer membranes of all our cells and insulating nerve fibres, helping signals travel properly to and from the brain. It’s also a fundamental part of the endocrine system, as all steroid hormones (eg oestrogen) are synthesised from cholesterol. A good diet and regular exercise can keep cholesterol within a healthy range for most people.