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.

Carbohydrate loading (commonly known as carb loading) is when bodybuilders and endurance athletes eat a high number of carbohydrates in a single day or over a series of days in preparation for a competitive event.

Conceptually, carb loading is the same for endurance athletes (runners, cyclists, etc) and bodybuilders.  It’s about planning periods of high carb and low carb intake to balance energy stores. However, each group has a drastically different reason for loading up.

Endurance competitors carb load to increase the amount of fuel available to their muscles. According to the theory, this extra energy storage helps them improve their endurance 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?

multigrain bread

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

Your body breaks down carbohydrates into sugar that enters your bloodstream and gets stored for energy use in your muscles and liver as glycogen.

Your muscles usually only store small quantities of glycogen. And when you exercise, you deplete your energy storage.

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 shown mixed results … women may need to take in more calories than men during carbohydrate loading to experience the same gains in glycogen.

So theoretically, the reasons certain people carb load are either because they want to a) “build up” stores of glycogen so they can use this extra energy storage to help improve endurance during long sessions and/or b) fill their muscle with glycogen so they pull water into the muscle, helping them gain mass and tone.

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 increase their energy storage 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.
  2. Bodybuilders and fitness athletes, who use carbo-loading to gain size and mass before bodybuilding 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 vary greatly from person to person. Make sure experiment before the next big bodybuilding competition.

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

powerlifting male

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 body weight, according to Jim Stopanni, Ph.D.

Bodybuilders looking to attain that “shredded” look right before a competition are known carb load with foods that are low fat, and high carb, 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 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 athletes include fruit, sports drinks, quinoa, beans, lentils, oats, corn, and potatoes (although be careful with the fiber-rich foods 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 carb meal 3 hours before exercise, increases muscle glycogen levels by 15%.

Remember, 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 meal rich in carbohydrates 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 retention of glycogen leading up to an endurance event.

Foods High in Carbohydrates

Here are some nutritious foods high in carbohydrates:

Food Portion Size Carbs (grams)
Oatmeal, cooked ½ Cup 15
Beans/legumes/lentils ½ Cup 15
Hummus ½ Cup 10-15
Pasta, cooked 1 Cup 45
Rice, cooked 1 Cup 45
Potatoes (hashed, mashed) ½ Cup 15
Squash (winter type: acorn, Hubbard, etc) 1 Cup 10-30
Sweet Potato/Yams-plain cooked 10oz 60
Cow’s milk (fat-free, 1%, 2%, Whole) 1 Cup 12
Rice Milk 1 Cup 20
Soy Milk 1 Cup 8
Yogurt (plain) 1 Cup 12
Apple 4-8 oz 15-30
Banana 6” – 9” 30-45
Blackberries, Blueberries 1 Cup 20
Cantaloupe, Honeydew Melons 1 Cup 15
Cherries 12 15
Grapefruit ½ Large 15
Grapes 15 small 15
Kiwi 1 small 15
Orange 1 medium 15
Pear 6 oz 20
Pineapple 1 Cup 20
Raspberries 1 Cup 15
Strawberries 1 Cup 12
Watermelon 1 Cup 12

Side effects and risks of carbo loading

As we’ve seen, carb loading may help you, increase your glycogen levels, increase endurance and mass, and improve 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 carb-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 carbohydrates. 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, a low carb diet might be better for you.

But if you are a runner looking for a boost in your next race or a bodybuilder looking to make noise in the world of bodybuilding, carb loading may be right for you.


Editor’s Note: This post was updated on October 1, 2018for accuracy and comprehensiveness. It was originally published on April 20, 2016

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.

Article provided by InBody