Dear doctor; I keep hearing people talk about cholesterol or even read but no one ever seem to exhaustively explain what it is. What are cholesterol and what do they do in the body? Anonymous M. Dear Anonymous M, Cholesterol is one of the natural fat substances of the body and is a soft waxy substance. Cholesterol is used for lining the cells of the body, for carrying hormones and is also useful for various metabolic processes in the body. It also provides calories to the body. Cholesterol is moved in the body by binding with proteins known as lipoproteins. These can be high density (HDL) and low density (LDL) proteins. Liver is the main organ to produce cholesterol in the body. Food items like animal fats, milk products, eggs, deep fried oily substances are rich in cholesterol. Whereas vegetables, fruits and nuts have no cholesterol. Though an essential substance for the body, excess of cholesterol (which is not disposed off by body) contributes to obesity and related problems. It blocks blood vessels of the body by forming fat deposits inside and increases risk of heart diseases, cramps in legs, orange discoloration around eyes. HDL cholesterol is healthy and higher levels protect the heart whereas LDL cholesterol is unhealthy and contributes to heart diseases. Smoking lowers protective HDL levels in body. Therefore, it is advisable to take a low cholesterol diet to avoid these problems. Good amount of physical activity also helps in keeping cholesterol levels low.