Some say that you need fast-digesting carbs after a workout to replenish glycogen, spike insulin and gain muscle.
But, you may also come across claims that taking in carbohydrate after exercise will stop you burning fat.
Making the Case for Carbs After a Workout
If I wanted to make a case for the importance of taking in carbs after a workout, it would go something like this:
After a tough workout, your body is depleted of glycogen – the name given to carbohydrate stored in your body – which needs to be replaced as soon as possible. Failure to do so is cheating your muscles and putting the brakes on recovery.
Stored glycogen in muscle cells will also pull water into those cells. This increases cell volume, triggering changes in the muscle that will ultimately lead to faster growth.
The best way to do this is with a rapidly digested carbohydrate with a high glycemic index. Dextrose, maltodextrin, waxy maize starch or Vitargo will all do the job.
The carbs also jack up your insulin levels, which helps to shuttle nutrients into muscle cells, as well as blocking the post-exercise rise in cortisol levels, which would normally have a catabolic effect on your muscles.
In short, to truly maximize recovery and muscle growth, carbs after a workout are essential.
Insulin will be spiked, cortisol will be shut down, and glycogen will be restored as the post-workout gods deliver you directly to recovery heaven.
Or will they?
Actually, they won’t.
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Post-Workout Carbs and Glycogen
It’s true that muscle glycogen is synthesized more rapidly if you take in some carbs immediately after a workout rather than several hours later.
In fact, delaying the consumption of post-workout carbs for just two hours has been shown to slow the rate of muscle glycogen resynthesis by as much as 50% .
Put differently, the speed of post-exercise glycogen synthesis is not important as long as the total carbohydrate need for the day is met.
Unless you’re doing multiple daily workouts, a decent muscle-building diet will provide enough carbohydrate to restore glycogen regardless of whether or not it’s taken immediately after training.
Think of it like putting fuel in your car.
Unless you were taking part in a race, the rate at which the pump dispenses the fuel into your car is of very little practical significance.
What’s most important is the amount of fuel that gets into the tank, rather than the speed at which it gets in there.
It’s a different story if you’re involved in a sport or activity where the length of time between exercise is relatively short.
The training practices of some athletes, for example, will often demand multiple bouts of exercise targeting the same muscle groups on the same day.
In this case, speeding up the rate at which glycogen is replenished takes on a much greater importance . You want those muscles ready for action again as soon as possible.
In other words, the speed of glycogen restoration is important for some people in certain circumstances.
But for most of us, it isn’t.
Do You Need Post-Workout Carbs to Build Muscle?
The idea that you need carbs after a workout to “spike” insulin levels and gain muscle is also a myth.
But this has little to do with changes in blood sugar levels. Rather, the amino acids in whey trigger insulin secretion directly in pancreatic beta cells. The branched-chain amino acids, leucine in particular, appear to be the most potent insulin secretagogues.
Whey also stimulates the release of a couple of gastrointestinal hormones known as GIP and GLP-1, both of which have the effect of raising insulin levels .
In one study, taking 50 grams of carbohydrate with 25 grams of whey protein after exercise failed to stimulate muscle protein synthesis or inhibit protein breakdown to a greater extent than 25 grams of protein alone .
The rise in insulin from protein alone is enough to inhibit the increased rate of muscle protein breakdown that normally happens after training with weights .
In other words, if you’re taking in a reasonable amount of protein after training, the addition of carbohydrate isn’t going to help you gain muscle any faster.
Dig through the research, and you’ll find very little evidence to show that the addition of post-workout carbs to a protein shake has any additional muscle-building benefits compared to the protein shake alone [4, 14].
How Do Carbs After a Workout Affect Fat Loss?
You may have heard that taking on board fast-acting carbs after a workout will sabotage your attempts to get lean.
The research on the subject is a bit of a mixed bag. Some studies show that taking in carbs after a workout puts the brakes on fat burning, while others show that it has no effect.
One trial, which looked at fat metabolism for three hours after a post-workout meal or plain water, shows little difference in the number of fat calories burned .
A study published in the British Journal of Nutrition shows that fat oxidation remains high even when a large bowl of pasta is eaten after exercise .
On the flip side, Colorado State University researchers found a marked drop in fat oxidation when a carbohydrate-rich mixed meal was consumed immediately after exercise .
A Canadian team also found that replacing the calories burned during exercise with a post-exercise milk shake limits the normal rise in fat metabolism that occurs after a workout .
However, all four of these studies have limited practical application, and here’s why.
If you really wanted to establish the effect of carbs after a workout on fat loss, you’d need to look at changes in body composition over a period of 2-3 months. Measuring fat metabolism during a narrow window of time immediately after exercise gives you a very limited picture about what’s going on.
To lose fat, all you need is an energy deficit. As long as a post-workout meal/shake doesn’t reduce or eliminate that deficit, it’s not going to slow your rate of fat loss.
In summary, there’s nothing wrong with taking in carbs after a workout.
It’s not going to stop you losing fat.
But nor will it make a great deal of difference to the speed at which you gain muscle, and is not as vital as was once believed.