Yes, fasting effects my hair every time. Shorter fasts can make hair healthier, but my two longer fasts (28-30 days) had very negative effects on the hair. But it depends on what weight you drop to. I got extremely thin. Skin and bones. So obviously the body will sacrafice sending nutrients to the hair follicle, but when you reach a certain low weight will grow creepy fine down all over the body, common in annorexia - as well as hair loss. It all depends on how thin you get, not the length of fast... For eg, when I fever for anything over 3 days I drop weight fast and half my hair usually falls out. Joy! Just the body responding to shock.
It will go into a severe shedding phase for three months then some of the follicles will lay dormant, for a while and after about 6 mnths your hair will start to get body, shine and movement. It might be a bit thin and limp in the 6 months.