this is not true; I do extended bikepacking trips nutrionally similar to the GP's experience and you feel amazing. Maybe your first time or the first day can be tough but the human body loves to move and consume. I think a good frame of mind is you're a high efficiency furnace pumping out the heat on a very cold day. but this machine actually heals & improves the more it's used!

That’s only true over a relatively short period.

Stuff you can do for a week doesn’t automatically extend to maintaining that over the next 50 years.