From plate to muscle: how do carbohydrates actually end up in your muscles? | DEEP DIVE

On this blog, I've written a lot about carbohydrates and energy: when to eat them, how much you need, and which types work best around your training. But there's one thing I've never really explained: what happens behind the scenes happens. How do those carbohydrates actually get from your plate to your muscles?

It's a complex chemical process, but I'm trying to explain it as understandably as possible. For those who have always wanted to know: this is your deep dive.

From bite to glucose: the journey begins in your mouth

As soon as you take a bite of pasta, rice, or bread, the party starts. Your saliva already contains a substance that immediately begins to break down carbohydrates. Carbohydrates are actually long chains of sugar molecules linked together, a bit like a string of beads. Your stomach and intestines keep breaking down that chain further, until only loose beads are left.

In your small intestine, those chains are completely broken down into the smallest building block: glucose. That is the form in which your body can actually use carbohydrates. Everything begins and ends with that one small molecule.

What this means for your training: The better you digest, the faster glucose becomes available. Stress or a sensitive gut can affect digestion, which can slow glucose availability. Therefore, eating calmly before a workout is not an unnecessary luxury.

Glucose in your blood, and your body already responding

Once broken down, glucose is absorbed from your small intestine into your blood. Your blood sugar level rises, and your body picks up on that signal immediately. An interesting detail: your body actually starts to react even before the glucose is in your blood. Just seeing and smelling food sends a signal to your pancreas. By the time the glucose actually reaches your blood, your body is already ready to process it.

The reaction involves the creation of insulin, a hormone that can be seen as a key. This key is needed to open cells for glucose. Without insulin, glucose is as it were waiting outside a closed door, no matter how full your blood is.

What this means for your training: The speed at which glucose reaches your blood depends on what you eat. Fast carbohydrates, such as white bread or sports drinks, cause a rapid spike. Slow carbohydrates, like porridge or brown rice, provide a more gradual supply. Depending on the timing and intensity of your training, you make a conscious choice about this.

The muscle cells take up the glucose

Muscles have special “doors” that let glucose in, called GLUT4 transporters. When at rest, those transporters are hidden deep inside the muscle cell, but insulin pulls them to the outside. The door opens and glucose flows in.

What makes this extra interesting is that exercise does exactly the same thing. So your body has two ways of opening those little doors: via insulin and via exercise itself. That's also why exercise is so beneficial for your blood sugar levels. Your muscles absorb glucose from your blood during exercise via their own, independent mechanism, separate from what insulin does.

What this means for your training: Movement opens the doors, but the fuel itself must already be in there from your earlier meals. For a short, gentle workout, you don't necessarily need to eat carbohydrates just before. If you've eaten well the rest of the day, your glycogen stores are probably already sufficiently filled. However, for longer or more intensive exertion, the supply from your blood becomes increasingly important.

Filling the fuel tank

Once in the muscle cell, glucose isn't immediately burned. If you're not exercising, your body first stores it as glycogen: a type of starch that your body produces itself. You can compare it to a compressed battery ready for use. Your muscles can store around 300 to 500 grams of glycogen, and your liver adds another 80 to 100 grams on top of that.

Your glycogen stores are your personal energy reserve for your next training session. The fuller that tank is when you start, the longer and harder you can perform before you feel it in your legs.

What this means for your training: Your glycogen stores aren't replenished from one meal to the next. It's a process of hours. Anyone who trains daily and structurally eats too few carbohydrates is always riding with a half-full tank, and that's precisely what you want to avoid.

During training: the tank opens

As soon as you start moving, your muscles tap into those glycogen stores. Glycogen is broken down step by step into glucose, and that glucose enters the furnace: the mitochondria of your muscle cell. There it's converted into ATP: the direct energy source for every muscle contraction. Without ATP, your muscle simply cannot contract.

During intense exercise, such as high resistance on a spinning bike or a heavy set in the gym, this process happens extremely quickly. With sustained high intensity, you can completely deplete your glycogen stores in 60 to 90 minutes. And you'll certainly feel that.

What this means for your training: The familiar heavy legs, the dip halfway through a long endurance run, or the feeling that your strength suddenly gives out. This is often not a lack of motivation, but simply an empty glycogen tank. Sound familiar? Then your nutrition around training is the first thing worth looking into.

What does this mean for your training?

Now that you understand how the system works, the logic behind sports nutrition advice becomes much clearer. Eating carbohydrates before a workout isn't just a habit. It replenishes your glycogen stores, ensuring you start with a full tank of energy. During prolonged exertion lasting more than 60 to 75 minutes, that tank slowly depletes, and topping it up along the way with a gel, sports drink, or a ripe banana helps maintain your performance.

After training, something else interesting happens. Those little doors in your muscle cells are still fully active and wide open. In the two hours after exercise, your muscles absorb carbohydrates faster than normal, with uptake being greatest immediately after training and gradually decreasing. So, eating quickly after a workout isn't a myth, it's simply biology.

Carbohydrates as an ally

Carbohydrates aren't the enemy. They are your muscles' primary fuel, and if you understand how the system works, it also becomes easier to make smart choices. Which carbohydrates you choose, when you eat them, and how many you need, depends on your sport, your intensity, and your goals. That's precisely what sports nutrition is all about.

Would you like to delve deeper into this? Then sign up for the free Masterclass Sports Nutrition Basics.