Fasting and veganism

How can people fast for weeks and months without food, and only water?  Jains have a tradition of fasting, from the one day fast that I observed yesterday, to the 8 day fasts that many are doing during paryushan, to the 32 day fast that one high-powered business person is doing in Boston, to the many months that some extraordinary sadhus and sadvhis and exceptional laypersons fast. Since modern medicine doesn’t have an answer to how people can fast for long periods of time,  we are left to conclude that the body must have some adaptive processes of which we are not aware.  Still, at some point, we all need to eat. If we can learn, from fasts or otherwise, to control our cravings and get away from a deficiency mentality, it may be easier to transform our usual diet, avoid dairy productsand eggs, and go vegan to more fully realize our ideal of ahimsa.