Why? Melanin gives hair its pigment, and copper is crucial in melanin production. Walnuts are rich in copper.
Why? Zinc helps keep color in your hair, so presumably foods that are rich in zinc will keep you from going gray. In addition to shellfish, zinc-rich foods include sunflower seeds, cashews and yogurt.
Why? If you don't get enough vitamin B12, it can cause your hair to become dry, thin and prematurely gray. Chicken, as well as eggs, cheese and milk, are packed with vitamin B12. Some claim that large doses of certain B vitamins -- B6, B12 and folic acid -- will reverse the process of graying in three months. (Before you take massive doses of any vitamin or mineral, do consult your family doctor.)
Why? Folate (or folic acid) has been linked to better hair health, while lack of it has been linked to premature graying. Folic acid is found in broccoli, asparagus, beans, peas and lentils. Many foods in the United States, such as pasta, bread, rice and cereals, have been fortified with folic acid.