Deuteronomy 9 records that Moses stayed on top of Sinai for 40 days and nights and he claims: ‘I neither ate bread nor drank water’ (Deut. 9:9). That reminded me of an article I read about Jesus having to build up to fasting for 40 days and nights. It is such an arduous task to fast for that long that he would have required regular fasting on the build up. You cannot simply decide to fast for 40 days and nights from scratch. Dizziness, headaches and all kinds of mental struggles would kick in early in the process, unless you trained yourself in advance.