Nutrients are broken down and converted into energy for normal metabolic function. Energy metabolism is generally divided into two types, aerobic and anaerobic. In aerobic metabolism, oxygen is used to produce energy, with carbon dioxide and water as a by-product. However, 1-2 percent of this oxygen is not used, resulting in the formation of free radicals, or reactive oxygen species (ROS). These free radicals can damage DNA and lipids and contribute to degenerative changes throughout the body. Antioxidants are responsible for removing and inhibiting the formation of ROS.