Mark Macdonald: The Myth of Carb Loading

Growing up as an athlete the majority of my coaches recommended carbohydrate loading the night before a match.

The thought process behind this is that by eating complex carbohydrates (that huge bowl of pasta or plate of mashed potatoes) the night before your competition, your muscles will fill up with stored sugar (stored glucose is called glycogen).

This is then supposed to provide your muscles with more fuel during your competition, allowing you to have better endurance and more energy as you enter the later sets in a match.

From the surface, it seems to make sense and many still think this way of fueling will give them the edge during the crucial points and games.

However, this is why myths are created. They all look good on the surface, that’s why they have survived over the years.

Once you begin to pull back some layers and dig a little deeper, the holes begin to appear and the reality is carb loading actually hurts your performance on the court!

Let’s dive into the 3 reasons why:


Your body doesn’t store glucose (glycogen) efficiently, triggering excess carbs to be stored as body fat

In the first blog of this series – How to Eat like a Tennis Champion you learned that your body needs to be consistently fed to have consistent fuel and you do that by eating PFC Every 3.

The reality is the only thing your body is efficient at storing is fat, because it provides so much energy.

Your body stores glucose (sugar) primarily in two places: your liver and your skeletal muscle (the muscle you use to play tennis.)

At best, your liver can store about 100-120 grams of glucose. That’s only 400-480 calories (4 calories per gram of glucose)!

This is crucial to understand because the glucose stored in your liver is your body’s source of blood sugar.

Here’s an illustration showing the two places glucose is stored in your body and how it’s used for energy:

When your blood sugar drops; your liver releases glucose into your blood to keep your blood sugar stable. When your liver runs out of glucose, it begins to convert amino acids (muscle) into sugar.

This is how low blood sugar triggers your body to consume its muscle.

Here’s an illustration showing what happens when your Blood Sugar crashes:

Your skeletal muscles can store more glucose than your liver.

However, when you carbohydrate load, you spike your blood sugar. This causes your body to store fat as well as glucose.

Whenever there is an excess of glucose in your body, most likely some of it will be stored as fat.

In addition, anytime you spike your blood sugar, you create unstable blood sugar levels. This goes against the science of eating PFC Every 3.

Here’s an illustration showing what happens when your Blood Sugar spikes:


The stored sugar (glycogen) in your skeletal muscle cannot be used as blood sugar, causing your body to convert amino acids (Your Muscle) to glucose. Which means you are losing muscle!

This philosophy also came into being because people have always thought that all of the stored glucose in your muscle can be utilized by your body for energy.

There’s one big problem with this philosophy: it’s impossible!

As you saw in the “where glucose is stored” illustration, your skeletal muscle lacks the enzyme glucose-6 phosphatase. Without this enzyme, your skeletal muscle cannot pass glucose into your blood, which prevents it from providing the rest of your body with needed glucose.

The stored sugar in your skeletal muscle can ONLY be used by that muscle.

During a tennis match your body will utilize certain muscles more than others, which means that once your more active muscles (legs, glutes, calves, arms) run out of stored sugar, they have no more fuel.

This lack of fuel is the feeling you get when your legs feel extra heavy or your swing loses it power.

These energy deprived muscles are now panicking and becoming reliant on your liver for energy.

Most likely, if your muscles are out of fuel, then your liver is out of its stored glucose. This triggers your liver to begin converting amino acids (muscle) into sugar in order to provide your muscles with fuel (as you saw in the “where glucose is stored” illustration).

This entire process will greatly negatively affect your performance on the court especially later in the match when every point counts!


You will experience energy drops during competition which will negatively affect your performance and recovery

The first two reasons will cause you to have energy crashes during your competition because the lack of available glucose in your body triggers low blood sugar.

Low blood sugar is always accompanied with low energy.

In addition, carbohydrate loading the night before will ensure that you begin your competition with unstable blood sugar, which will lead to energy challenges throughout your match and make your recovery for the next match that much harder.

Optimal recovery is created by consistent fuel during your training and your match.

There you have it! You now possess the knowledge why you should never carb load. It’s time to throw that faulty concept out!

The facts are that your body needs to be fed consistently before, during and after your competition, which is exactly what you’ll learn in the remaining three articles in this series:

- Part 1: Eating Like a Tennis Champion

- Part 3: Optimally Fueling Before Your Match

- Part 4: Maximizing Your Recovery After Your Match (coming June 30, 2017)

- Part 5: Winning the Final Set - How to Fuel During Your Match (coming July 5, 2017)

And the next time a friend tells you to carb load, you can educate them on the real facts!


About Mark

Most important, Mark Macdonald is a husband to his wife Abbi and father to their 12-year-old son Hunter and 2-year-old baby girl, Hope.

Professionally, he’s a world renowned nutrition & fitness expert, best-selling author, television personality, international teacher and speaker, and entrepreneur who has coached everyone from celebrities to athletes to business executives to busy moms on how to permanently get their body back with cutting edge nutrition, fitness and lifestyle strategies.

He is the founder of Venice Nutrition and the IBNFC: International Board of Nutrition and Fitness Coaching, author of the New York Times Bestselling books Body Confidence and Why Kids Make You Fat and How to Get Your Body Back, as well as a featured health expert for many national media outlets, a few being: Dr. OZ, CNN, HLN, Access Hollywood, NBC, FOX and Chelsea Lately.

Mark is also a sought after keynote health speaker and continually speaks throughout the world.

You can learn more about mark @ as well as read his full bio @

- For Adults - Our 8 Week Plan - it's a powerful plan that has helped a couple million people rock their health, it's a global plan and featured in my why kids make you fat and how to get your body back book. Here is the website -

- For kids, we have a powerful Kid Athlete program that supports the info in the 5 Part series and connects perfectly with the 8 Week Plan so tennis families can rock it together - all the info about that is on

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