You can figure out whether you need a post-workout meal pretty easily. Let’s start by estimating about how much storage carbohydrate energy you have on board to start with. Your maximal carbohydrate storage is approximately 15 grams per kilogram of body weight [15 grams per 2.2 pounds]. So a 175-pound athlete could store up to 1200 grams of carbohydrate [4,800 calories]; enough energy to fuel high intensity exercise for quite some
time.
So let’s say this 175lb person eats a bowl of oatmeal with some peanut butter (~600 calories), then goes on a 2 hour bike ride at 600 calories per hour. They arrive home at a 600 calorie deficit. Meaning they have 4200 calories of storage carbohydrate STILL ON BOARD.
Now, they hear about this post-workout need, and rush off to eat so they can have a “good workout the next day”, but is that really necessary. Let’s look at how long it would take to replace glycogen, or storage carbohydrate.
Unfortunately, in the scientific literature, glycogen restoration rates are measured in funky units like glycosol per gram or mumol.g wet wt-1.h-1, or mmol/kg – tough to translate into actual real world numbers for us normal folks. But I’m going to try.
5mmol of glucose is 1 gram. Assuming the glycogen is cleanly broken down into glucose, then 5.5mmol of glycogen is 4 calories, since there’s 4 calories in a gram. Post-exercise glycogen re-synthesis rates fall right around the 10mmol/kg/hr range, which is 4.5mmol/lb/hr, so for a 175lb individual, you looking at 785mmol/hr, which is 157g/hr, which is 630 calories per hour.
In other words, a conservative rate of glycogen re-synthesis for you is 630 calories per hour, for up to 2 hours after exercise. So why the heck would you be trying to replace glycogen stores by shoving 800 calories of carbohydrate down the hatch just 20-30 minutes after exercise?
Your goal after a typical workout should instead be to A) re-hydrate and B) elevate amino acids to limit muscle catabolism by consuming 0.25g protein per lb of body weight, with a small amount of sugar to elevate insulin levels. So, for example, the 175lb person could eat about 45g of protein power mixed into 100-200 calories carbohydrate (i.e. a couple bananas with a couple scoops whey protein).