[sambeau]

When I fasted I remember the feeling of energy kicking in around day 2-3. I had moments of supreme clarity but also moments of fuzziness. The energy boost was real though. I continued to exercise quite heavily so didn't't see any muscle loss. I'm quite a big guy so there were a lot of fat reserves to melt—my skin became very greasy as if I'd eaten a very fat-heavy meal, I could even taste the oil in my mouth.

I wonder if, if you are not a big eater, then the difference might be less than if you tended to be full of food, digesting away all day and night. Similarly, if there's not a lot of fat on you maybe, rather than burning fat with an energy boost, you end up burning muscle and feel tired?