It seems the consensus is that Moses’ fast was effected by God.
When it comes to the issue of Jesus’ fast, it seems we should be considering the fact that he was and is the God-Man which may well have affected how his human body could function. Yes he laid aside his divine attributes to accomplish his earthly assignment, but I believe the exact nature of the hypostatic union boils down to mystery, plain and simple.
The Word-Faithists claim he accomplished his miracles by virtue of Holy Spirit baptism which is untrue, and no such thing exists at any rate. He performed his miracles because he was God himself. E.g. his walking on water.
I believe he accomplished his fast either through the Providence of God as did Moses, or because he was and is the God-Man.
Lots of people all over the world have gone 40+ days without food on nothing but water. I'm one of them. All it takes is a reasonably pure diet beforehand and a comfortable bed....
And practice so we don't misinterpret symptoms we experience. That's easy. Just read books on water fasting. Its not very complicated.
Now there are a few people that claim they can go long periods with dry fasting (no water). Personally I don't believe them. I'm still curious if its possible somehow and even if there are benefits to it.
There's another factor that nobody has mentioned about Moses who went 40 days without food or water. Look at that region he was in. Not that we know exactly what it was like back then but have you ever seen a river near the top of a mountain? Where exactly would the water come from? I don't think there was any water up there available which would explain why God would have had to intervene if He wanted Moses to remain up there for an extended period and 40 days is a very extended period.
Most Biblical references to fasting imply that someone desired greater connection with God and didn't interrupt their prayer with food because it would break up their prayer time. This actually makes a lot of sense, just as much then as today. We all hate interruptions of any kind. They stop our mental flow, our concentration. And eating would definitely interrupt whatever they were praying about. Basically it gets in the way.
It also might tell us that their prayer wasn't just for a few minutes. It was long enough that it interrupted one or more meals. How often do you hear of anyone today praying for 6+ hours at a stretch doing nothing else? That takes strong commitment. (What is interesting is when you're fasting you're pretty weak and spend most of your time lying in bed daydreaming. This makes for a perfect opportunity to commune with God and pray. And to reflect on your life, both the positive and negative. After a few days though you tend to focus on the positive and it becomes very mentally uplifting. This hugely counteracts the mental boredom that naturally occurs when you don't have the energy to do much of anything! Our mental disposition just ramps up a lot after a few days.
Esther 4:16
Go, gather together all the Jews who are in Susa, and fast for me. Do not eat or drink for three days, night or day. I and my attendants will fast as you do.
Exodus 34:28
Moses was there with the LORD forty days and forty nights without eating bread or drinking water.
If anyone knows of any other examples of dry fasting or fasting with no water please let us know. Someone would have to be mighty well hydrated to go 3 days without water and food. Most medical people claim we can't live without water for 4 days but that's in situations with no preparation, like when you get buried in an earthquake. In the wilderness people usually ration their water so they were probably in a state of severe dehydration for many days before they died. This doesn't tell us much about how it would be if the person was well prepared. No salt intake for several days + lots and lots of water for several hours before they start. Almost everyone out there is not well hydrated.
