but is there really any truth to this? calories in vs calories out in the day VS meal timing??
Yes there is some truth to this, caloric balance is #1 priority, but the science can not be denied that there are biological differences surrounding training that give favorable nutrient partitioning effects. Does this effect total calories consumed, no but it definitely effects whether they are stored in the muscle as glycogen, burned in general daily use or are converted and stored as fat.
I think most estimates I have seen regarding what each of the factors have to do with composition tend to follow along these lines.
Caloric Balance 90%
Macros 5%
Meal Timing 5%
So if looking at that you can still get an A = 90% just off of caloric balance, that says a lot! The others have a pretty minimal effect, but an effect nonetheless. If an A is good enough no need to tweak things but if you want an A+ then I would say it is worth the extra effort.
Insulin Sensitivity, and Glut 4 reaction during and following resistance training are really the tweakable factors when it comes to macros and meal timing. Adding up to around 5% a piece and that is a generalized estimate based off of anecdotal evidence from what I have read. I would say that is probably immeasurable due to personal difference, but we all know that each macro requires different amounts of energy to digest, as well as having different hormonal reactions to their ingestion. So those things are measurable and proven and definitely have an effect on what happens to the calories consumed.
Think of it like this, if nutrients were cars at a busy intersection you are going to get more cars through to the appropriate places if you employ a traffic cop to direct traffic more efficiently. The only time that police officer is on duty directing nutrients more efficiently is postworkout.
It is definitely going to have a positive effect but yeah it is nothing compared to caloric balance.