Lutein is a nutrient found in leafy green vegetables like spinach and kale. It is also responsible for the yellowness of chicken skin, and fat, but is not fatty itself. In the body it’s employed as an antioxidant, but its most important function seems to be in the eye. Lutein concentrates in the eye and is responsible for some of its pigmentation. Its concentration there is hypothesized to keep the eye safe from light damage, and increased pigmentation has been correlated with a reduced risk of macular degeneration and cataract development.