I get this question a lot from clients - Should I have a different set of macros or calorie intake for my non-training days? But the answer may not be as simple as most think. To understand better, it helps to know how glycogen works in the body through what you eat.
What is glycogen?
Glycogen is a polysaccharide (a sugar) which is the body's main way of storing energy in the muscles. When carbohydrates are present in the diet, the liver converts the glucose (sugars) of the food into glycogen to be stored in the liver and muscles for exercise use. These are our energy stores for movement. When we exercise, we deplete our glycogen stores over time. Think about doing a large amount of push ups - at some point you can no longer push yourself of the ground and your muscles begin to fail. This is glycogen depletion. Your muscles no longer have the energy needed to perform the movement.
When it comes to macronutrients in athletes, carbohydrates are our main source of fuel for energy in our workouts. It can, of course, become far more complicated by introducing nutrient timing, though we won't touch on that right now.
The common misconception is that for days where you aren't using as much energy in the form of exercise (aka rest days) you don't need to eat as much energy in the form of carbohydrates.
If you're doing this for physique purposes ONLY, this ideology works. If you're looking for performance improvement or to simply be fueled for your workout (i.e. CrossFiters and most of my clients), however, this does not work.
The human body functions on mildly deficient stores regularly. Glycogen is synthesized and re-synthesized within a 24-36 hour window. This means that what I eat today with my synthesized into glycogen in the next day to day and a half.
So let's say Thursday is your rest day. If you eat less carbs on Thursday, when you go to workout the following day on Friday, you will be very glycogen deficient, likely performance poorly, and well like crap through your workout. So now you're thinking, in order to have lower glycogen levels on rest days, it would benefit you to have lower carbohydrate intake the day prior to your rest day (Wednesday). This however can also directly effect your workout that day and not allow you to recover properly from your workout if you're not refueling your muscles directly following your workout.
The best option is to have the mindset that your rest days are re-feed days and treat these as recovery days where you are not lowering your caloric intake, but ensuring that you have sufficient glycogen stores for training in the upcoming days.
For this reason, I don't prescribe my performance-based athletes training day macros and rest day macros. For personalized nutrition plans, including macronutrient profiles to incorporate nutrient timing to fuel your workouts, click here or email me at firstname.lastname@example.org