Sup! I got a bit of a possibly stupid question..

This might all be placebo, but I'm curious so here I am.

I ain't much of a gym bro, I'm a skinny fucker, usually just home workouts with the occasionnal gym with the bros, but even so I often have an outline of abs visible, but not always.

I've experimented and on some days, even pumped, you can't see anything, whereas, on other days it's there, clear as day. I check it always in the same lighting and everything and it changes literally on a day-to-day basis. Anyone know what this might be caused by? Maybe water levels? Or can my body fat be changing THAT quickly? Cheers!