To date, about 600 different carotenoids have been discovered. Carotenoids are fatsoluble nutrients that help give orange, red and yellow color to various plants and, in some cases, are associated with chlorophyll. Since these compounds were first isolated from carrots, they are called carotenoids. There are about 20 different carotenoids present in human plasma. The five most abundant in human plasma are lutein, lycopene, beta-cryptoxanthin, alpha- and beta-carotene. The best known member of the carotenoids is betacarotene. It is an antioxidaot that helps stimulate the immune system and protects against some types of cancer In addition to acting as an antioxidant on its own, beta-carotene has the ability to produce two molecules of vitamin A. Other carotenoids lack this ability. Alpha-carotene, for example, is only half as efficient in producing vitamin A as beta-carotene, while lycopene lacks the ability to form any vitamin A.