Carb Loading Explained

Published on June 21, 2017 by Contributing Author

You've probably heard the term carb loading thrown around, especially around athletes right before a big race as they stuff their faces with mountains of bread and spaghetti.

Carb loading (or “carbo loading”) is when endurance athletes, bodybuilders and fitness competitors eat a high number of carbs in a single day (or over series of days) in preparation for a competitive event.

Conceptually, carb loading is the same for endurance athletes and bodybuilders.  It's about planning periods of high and low CHO intake to balance energy stores. However, each group has a drastically different reason for loading up on carbs.  

Endurance competitors carb load to increase the amount of fuel available to their muscles. According to the theory, this helps them improve performance during a long run, bike ride, or swim.

On the other hand, bodybuilders go through a carb loading cycle as part of their pre-competition routine. Why?

Because they believe carb loading (at the right times and with the right balance of macronutrient and electrolyte consumption/depletion) can lead to a bigger, stronger, tighter looking physique.

But what does the science say about carb loading? Does it work? Is it safe?

In this article, we’ll explore those topics in more detail.

Let’s get started.


Why carb load?

First, a little primer on carbs:

Carbs, aka carbohydrates, are macronutrients that serve a very important function in your body: They are the body’s main energy source.

Your body breaks down carbs into sugar that enters your bloodstream and gets stored in your muscles and liver as glycogen.

Your muscles usually only store small quantities of glycogen. And when you exercise, you deplete these stores. 

In men, a carbohydrate-loading diet can raise glycogen storage levels in your muscles from 25 to 100 percent of their normal amount. Studies on carbohydrate loading in women have showed mixed results … women may need to take in more calories than men during carbohydrate loading to experience the same benefits.

So theoretically, the reasons certain people carb load are either because they want to a) “build up” stores of glycogen so they can endure long bouts of exercise and/or b) fill their muscles with glycogen so they pull water into the muscle, making it appear larger and more toned.

Let’s scrutinize each of these a bit further.

Who is carb loading for?

As we mentioned, carb loading is a strategy employed mainly by two groups of elite athletes:

  1. Endurance athletes, who use it to help them store more energy for long runs, bike rides, swims, etc. For these types of athletes, when timed effectively, carb loading has been shown to increase muscle glycogen, which can in turn lead to improved performance. Carb loading has been shown to help cyclists improve performance.
  2. Bodybuilders and fitness competitors, who use carbo loading to gain size and mass before competitions. However, some researchers advise exercising caution. A paper published in the Journal of the International Society of Sports Nutrition stated that “If carbohydrate loading is utilized, a trial run before competition once the competitor has reached or nearly reached competition leanness should be attempted to develop an individualized strategy.” In other words, the timing and efficacy of a carb loading varies greatly from person to person.

How to carb load (and what to eat)

How you carb load will depend on what you’re trying to accomplish.

Bodybuilders and fitness competitors

If you’re a bodybuilder or fitness competitor who is prepping for a contest or photo shoot, try carb loading roughly 2-3 days before your event. (again, it may take some trial and error to get the timing right, depending on your current body composition and metabolism).

Shoot for 3-4 grams per pound of bodyweight, according to Jim Stopanni, Ph.D. 

Also, bodybuilders looking to attain that “shredded” look right before a competition are known to stick with low fat, high-carb sources like potatoes and sweet potatoes, as opposed to oatmeal and pasta, which retain more water and may decrease vascularity (bodybuilders avoid water right before a show to achieve a tighter, more toned looking appearance).

Endurance athletes

If you’re an endurance athlete prepping for an event, increase your carb consumption to about 4 to 7 grams of carbohydrates per pound of body weight at least a couple days before your race. Endurance athletes, unlike bodybuilders, can load up on pasta and grains. Other good sources of low fat, carbohydrate-rich foods for marathon runners, triathletes, or endurance competitors include fruit, sports drinks, quinoa, beans, lentils, oats, corn, and potatoes (although be careful with the fiber-rich carbs like beans and lentils if they cause digestive discomfort … you don’t want to be racing toward the toilet on game day).

 Researchers have also found that eating a high carbohydrate meal 3 hours before exercise, increases muscle glycogen levels by 15% with high glycemic carbs.

Also, for endurance athletes it’s still important to replenish your body's energy during the actual event to maintain your blood sugar levels (any triathlete can attest to this).

One easy way to do this is by periodically eating and drinking sports drinks, gels, or bars, fruit, or candy (30 to 60 grams an hour should suffice).

Eating a carb-rich meal after your race is important too to replenish those glycogen stores.

Don’t underestimate the importance of rest either.

The combination of carb loading and decreasing activity appears to improve your body’s ability to store muscle glycogen leading up to an endurance event.

Foods High in Carbohydrates

Here are some nutritious foods high in carbohydrates:


Portion Size

Carbs (grams)

Oatmeal, cooked

½ Cup



½ Cup



½ Cup


Pasta, cooked

1 Cup


Rice, cooked

1 Cup


Potatoes (hashed, mashed)

½ Cup


Squash (winter type: acorn, Hubbard, etc)

1 Cup


Sweet Potato/Yams-plain cooked




Cow’s milk (fat-free, 1%, 2%, Whole)

1 Cup


Rice Milk

1 Cup


Soy Milk

1 Cup


Yogurt (plain)

1 Cup



4-8 oz



6” – 9”


Blackberries, Blueberries

1 Cup


Cantaloupe, Honeydew Melons

1 Cup






½ Large



15 small



1 small



1 medium



6 oz



1 Cup



1 Cup



1 Cup



1 Cup



Side effects and risks of carbo loading

As we’ve seen, carbo loading may help you feel less fatigued and experience an improvement in your performance. However, carb loads aren’t effective for everybody.

Whether you’re a triathlete or aspiring bodybuilder, other factors come into play that may impact your athletic performance and/or the effectiveness of your carbo-load strategy (e.g., your current fitness level, how much water you drink, and the intensity of your exercise sessions).

Carb loading isn’t a silver bullet against muscle fatigue … if you run/bike/swim for over 2 hours straight you’re going to get tired.

There are some inherent risks that come with eating mass quantities of any macronutrient, including carbs. You may experience side effects such as GI discomfort, cramping, and gas. Temporary weight gain is also another side effect. Carbohydrate loading can also affect your blood sugar levels, which may be troublesome for those with pre-diabetes or diabetes.

The bottom line: carb loading isn’t for everyone.


Carb loading is a dietary strategy that can yield better results for endurance athletes, bodybuilders and fitness competitors.

However, we should note that carb-restricted, high protein diets have been shown to be the most effective for decreasing fat mass while simultaneously increase lean muscle mass (which is the goal of most of our readers).

 If weight loss or fat loss is your goal, this might not be the best diet for you.

Regardless, carb loading may be an effective approach if you’re into endurance exercise or bodybuilding.


Scott Christ is a health and wellness entrepreneur, writer, and website strategy consultant. He's also the creator of the world's healthiest plant-based protein powder.

Tagged: Body Composition › Nutrition ›

Contributing Author
Contributing Author | Author
This article was written by a contributing author not affiliated with InBody. The views and opinions expressed here are those of the author alone and may or may not reflect those of InBody. If you have any questions about this article, please contact

Sign up for weekly blog updates