You get hungry and you start eating; in the words of Kant, that is not autonomy, but heteronomy. All non-human animals are heteronomous and submit their will to instincts, impulses and empirical desires. Humans, have the ability to shun the slavery to instincts, impulses, empirical desires, socio-cultural constructs etc. and become truly autonomous. That, I believe, is what fasting teachings us with the practice of not eating, when you get hungry. The lesson should not end here. Fasting should equip us with the ability to look beyond established paradigms, social norms, cultural bindings, conditioned desires and make us autonomous individuals who abide by laws that they have themselves inspected and accepted. Fasting is a journey from heteronomy to autonomy.