Carbohydrate Metabolism - Where your Workout Energy Comes From!

Carbohydrate Metabolism

Now that we’re all experts on what carbohydrates are, it's time to dive into carbohydrate metabolism - or how carbs work in the body. It’s probably easiest to do this with an example...

So let's pretend you had toast for breakfast this morning. You did have breakfast...didn't you?

The first part of digesting that toast begins when you wake up and think about having breakfast. That's right, you're body prepares itself for a meal! Your parotid gland secretes saliva and your stomach produces HCl with a truckload of digestive enzymes...all waiting to feast on your toast.

healthy carbs Your saliva contains an enzyme called amylase that breaks down starches and carbohydrates into smaller sugars. Along with your chewing, this system breaks it down far enough so that it can be transferred to the stomach through the esophagus.

Once the toast reaches your stomach, all those digestive enzymes break it apart, forming a liquidy mixture, called chyme. Your stomach contracts and pushes the chyme into your duodenum (upper part of the intestine) where the carbohydrate metabolism begins.

The carbs are completely broken down into simple sugars (like glucose and galactose) and absorbed through the intestine. Easy enough, right? Right!


So what happens to those simple sugars that are absorbed into the blood? There are actually several things that happen, but I'll just give you the lowdown on the important stuff.

Let's use glucose (a simple sugar) as our example. When glucose enters the blood from the digestive tract, it then enters the liver's portal circulation.

In other words, the liver is the first place your ingested glucose ends up. In the liver, glucose is taken up into the liver cells where it is then converted into long polymers, or chains, of glucose. A similar thing happens in muscles when there is "extra" glucose.

And viola! You now have storage for glucose! This is where you're going to harvest the energy for all of your workouts - your glycogen stores!

When you begin a workout, your liver and muscle cells have already begun to break down that high-energy glycogen right back into glucose. Glucose then enters the cells that require more energy. When it enters these cells, it runs down a long series of reactions known as glycolysis, the tricarboxylic acid cycle (TCA cycle) and oxidative phosphorylation.


This is a process in the mitochondrion that forms the end product - energy in the form of ATP. In other words, ATP is the major product of carbohydrate metabolism and is the main energy source for all muscle activity and bodily functions. So, remember, the mitochondria (below) produce all of your energy from glucose, which come from carbohydrates!

It's been shown recently that individuals with active lifestyles have a larger number of mitochondria in their muscle cells. This is another mechanism for the body to increase its energy production due to the increase in demand.

Remember, when your muscles increase the demand for energy, they also increase their demand for carbs! The more you workout, the more you need to supply your body with carbs in order to maintain muscle tone. Carbohydrate metabolism is the key!

Remember when we stored glucose as glycogen in the liver and muscle cells? What do you think happens when your glycogen runs out?

The answer is that you'll begin to break down your muscle proteins and use them for energy.

Fat deposits are actually the last form of stored energy that is broken down for energy in the body.

This has evolved as a survival mechanism throughout human history - we want to save all of our fat so that we can survive for longer periods of time without food. This probably occurred because of the lifestyles of prehistoric humans who would go days, even weeks without much food. Then, when they finally caught that buffalo, it was a feast!

Prolonged survival and endurance - this is what carbohydrate metabolism is all about! strength training exhaustion

Don't get the wrong idea! - it's not helpful to run yourself to exhaustion thinking that you're burning fat. The fact that you've been conditioning your muscles means that the amount of mitochondria in your muscle cells will increase (to produce more energy, since you've increased the demand for energy). And that only means one thing...

You'll burn fat and carbs when you're resting!

Remember, the purpose of glycogen storage is to prepare for physical activity. Your body won't metabolize carbohydrates quite as efficiently when you're resting. This is mostly a job for fat!

This is another key concept. It's not necessary to run yourself to the bone - just enough to feel good about yourself when you’re finished. It's easy to think that you'll burn a lot of fat if you exercise vigorously. Erase this thought!

The fact is that you burn stored glucose (aka glycogen) while you're exercising, and more fat while you're resting.

This is why strength training can be so satisfying! You work out, feel good about yourself at the end, go home and burn fat while you're reading a book! Of course, this assumes you're not following one of those low-carb/high protein fad diets...stay away!

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