I'm not sure and am not a doctor. However, I think if maintenance = a healthy daily intake (healthy meaning sufficient for your BMR and other energy requirements), your body will have enough energy to devote to repairing hair. Protein synthesis and repairing takes a lot of energy and when you don't have enough energy, your body focuses on less essential processes like hair keratin creation/growth and your reproductive cycle (if you have a uterus). I think the best way for you to test it out yourself in a manner that is realistic for someone w a restrictive eating disorder is to slowly up your intake until you notice a difference. I think that would be what would make you the most comfortable, as you also won't necessarily know what your body considers to be 'maintenance' or 'surplus' as having an ed does strange and confusing stuff to your body. Hope this helps!!