Also, can your body really efficiently utilize all of the micro/macro nutrients it needs in a day when it's handed them all at once?
I agree that IF can be a good little mental trick for a quick cut, but I'm skeptical on one meal a day for a life time and if there's any negative effects that could come up.
FWIW, it takes getting used to. If you drop everything and do a 24-hour fast after years of "6 meals a day", you will feel cold, irritable, and unproductive.
Also, coffee is a powerful thing.
The more involved answer involves talking about the sympathetic and parasympathetic nervous systems (SNS vs PSNS). The SNS is activated when doing things like going for a run, focusing on a specific problem, fight-or-flight, and other generally short-term "do things or have issues" situations. It does large systematic things that make your body better at overcoming the short-term obstacles in your life.
The PSNS, on the other hand, is responsible for more long-term survival goals. Sleep, digestion, relaxing, general awareness, etc.
Another important fact is that activating one of the circuits tends to deactivate the other. Eating activates the PSNS. Having "high energy" and not feeling tired/lethargic is basically a high SNS activation state.