One can eat as little as one can tolerate provided enough minerals and vitamins are taken - for instance, one multivitamin pill a day. This should also contain iron, selenium, cobalt and magnesium. If all protein and fat are excluded, there could eventually be a danger of damage to several organs including vision and liver function, but this varies with individuals. Obviously, famous dieters such as Gandhi did very well on very restricted diets and on periodic fasts. However, he was not doing this for personal or exaggerated health reasons, whereas many extreme dieters are, and they may lack the psychologic balance to have insight into whether they are going too far in their asceticism.