The amino acid L-lysine plays a part in the absorption of iron and zinc. Among plant foods, L-lysine is only found in high amounts in legumes, and a vegan who doesn't eat many legumes could find themselves falling short on lysine. In some women, iron supplementation does not lead to an increase in iron stores. But in one study, adding L-lysine (at 1.5 - 2 g/day for 6 months) to iron supplementation in such women did increase iron stores and decreased hair loss by one half.