Free radicals cause a chain reaction of "electron stealing" because the minute they start taking away electrons from other molecules, those molecules become free radicals themselves. Massive destruction ensues, leading to such disorders as Alzheimer's, cardiovascular disease, cancer, senility, and more. Antioxidant enzymes like superoxide dismutase, catalase, and glutathione peroxidase prevent oxidation by reducing the rate of chain initiation. This time, instead of waiting for the free radicals to make a long chain of free radicals, antioxidants scavenge initiating radicals and destroy them before oxidation is set in motion. The result is a rapid chain reaction which when left unattended can lead to various degenerative diseases such as heart disease, stroke, cancer, Alzheimer's disease, Parkinson's disease, memory loss, etc. Natural antioxidants are primarily derived from plants. The human body cannot produce its own supply of natural antioxidants; that is why we have to depend solely on our diet to get the amount of antioxidants our body needs. Scientists point out that this might be because consuming antioxidant fruits in food may provide a combination of lesser-known but potent antioxidant substances, which may afford greater effect than that of any single nutrient or individual antioxidant supplement. In a recent issue of the Journal of Nutrition, the total antioxidant content of several antioxidant fruits, including fruits, berries, vegetables, cereals, nuts, and legumes, was analyzed. Today's medical science has led to several wondrous discoveries about our health and the food we eat. You might be familiar with the saying, "An apple a day keeps the doctor away." And it's true because recent studies show that there are certain substances found in fresh fruits and vegetables that can be very beneficial to our health. They are derived from molecular oxygen under reducing conditions, such as when a person breathes. However, because of their high reactivity, free radicals often participate in unwanted side reactions resulting in cell damage. Many forms of cancer are thought to be the result of reactions between free radicals and DNA, resulting in mutations that can adversely affect the cell cycle and potentially lead to malignancy.