If you want beautiful healthy hair you have to feed it! You're hair on your head is very dead, but your follicles are alive. If you decide to eat badly, your hair may become deprived of it's much needed nutrients. Iron deficiency is one of the most common causes of hair thinning in  healthy women. If you decide to crash diet be prepared for the hair to start clogging the sink. It may actually fall out in clumps — a condition called telogen effluvium, you can even develop bald patches. Eat plenty of iron and protein rich foods.