It is interesting. Especially as you get older! At 43 now I still fluctuate 3-6 lbs overnight easily and my biggest fluctuation was 12 lbs in 24 hrs. And that's without any weird supplements/pills or whatever the fuck else is out there. I'll hit 230-232 after a weekend of snowboarding, drinking and eating garbage then back down to 225 within a day and a half with minimal effort. On my off days I usually really ease off on the carbs until the night before my next 4 on.
It took me roughly 8 months of a Nazi eating regime where I literally counted every grain of rice and tracked every macro, then gradually eased off of that to the point where I still prep and weigh my portions but if I want a slice of pizza one night I'm not gonna get all upset about those extra calories. Earn to burn, and burn to earn. Nothing like bro bodybuilders who think cardio is 15 minutes on a stationary bike yet get all upset when they can't "afford" a couple hundred extra calories that day. Gimme a break lol
That's why I say fuck all the science behind it because everybody is different and there's no trainer or nutritionist that can do for anybody what that person can do for themselves if they piece together the knowledge from dozens of sources but above all learn what their body needs and how it reacts, as opposed to throwing money at someone to tell them what to eat and how to lift, with their fingers crossed lol