The term carotenoids describes a group of fat-soluble pigments that are responsible for the orange, yellow and red colors of many vegetables and fruits. Carotenoids serve as antioxidants in humans, playing an important role in protecting cells from free radical damage. They also act as precursors to vitamin A, which is necessary for normal vision. The three most common dietary carotenoids include beta-carotene, alpha-carotene and lycopene. Each one has unique properties that promote optimum health in humans.