This question has bothered me a lot.
I have never quite understood it, and have spent years pondering and changing my diet because I was preoccupying myself over this; I didn’t want to put on any more fat than I needed to and wanted to gain pure, lean muscle.
The idea behind this is that on workout days your body is utilizing more energy and your muscles are more fatigued, so you need to eat in a surplus to make sure that you muscles repair and grow.
However, on non-workout days you are not working out, so there is no need to eat extra calories, as presumably the extra calories will just turn into fat as you are not fatiguing your muscles.
A lot of us forget that our muscles grow whilst we are resting; if we think of it this way we should be eating more on our rest days… however some studies indicate that the rate of growth is highest straight after a workout – so what should we do?
Stop sweating the small stuff
To keep it simple, to gain weight and build muscle we need to maintain a surplus in calories on average over a period of time.
Unfortunately, we will never truly find the ‘perfect’ answer to the exact rate that your muscles are growing at particular times after a workout, so we can’t precisely measure exactly how many calories to consume to only gain lean muscle.
Also, is it really worth the effort?
The most important lesson I have taken away from fitness is that if you could get 90% of the results whilst only using 25% of your effort, is it really worth using that other 75% for that final 10%?
Furthermore, worrying about things like this normally does more harm than good mentally… in fact, the obsession to only gain lean muscle was the reason I gained no muscle for a whole year – I actually lost weight.
Please, just keep it simple. Do not overcomplicate things and just eat in a surplus each day – this way you can almost guarantee that you will be building muscle without letting fitness take complete control over your life.
Got any questions about eating on rest days? Contact me at firstname.lastname@example.org or @Unigains on Twitter