An antioxidant is a lipid or water soluble molecule that slows down and in many cases even prevents the oxidation or break down of other molecules. Antioxidants are specific nutrients and enzymes found naturally in many foods including fruits, vegetables, and nuts. Unstable molecules and free radical damage can occur inside and outside the body. Metal rusting is a clear example of what can happen when oxidative stress occurs outside the body. When it occurs within the body, it can lead to cell dysfunction and the onset of problems like heart disease and diabetes.