Fwiw food and lack thereof modifies behaviour too.

If I fail to eat regularly for about 3 days I sink into a deep funk which takes a few days of regular eating to come out of.

I used to/have a problem where I just don't have the energy to eat due to being hungry and its a viscious cycle.

What happens when you fast?

Isn’t that failing to eat regularly?

No, because it's done intentionally.