Carbohydrate Loading for Improving Muscle Thickness

Let’s talk bodybuilding!

When you’re on stage showing off the physique you have trained and dieted so hard for so long to attain, you obviously want to impress the judges by looking the best you can at that very moment.

Not only does this require you to be lean enough, you also want your muscles to look as full and thick as possible. This is not a simple combination: to get as lean as possible, you can’t eat enough to maintain full-looking muscles.

A common practice to tackle this problem is for competitors to carb load the days before getting up on stage. This process usually consists of a depletion period followed by a loading period, where the competitor loads up on 8 to 12 grams of carbs per kilogram of bodyweight over a 24–48 hour period.

How much does carbohydrate loading actually improve muscle thickness and physical appearance, and are there any side effects? That’s what a new study set out to discover.


The researchers followed 24 top-level male amateur bodybuilders competing in the Amateur South American Arnold Classic in 2016. During the four days before the competition, the participants recorded everything they ate. The researchers then analyzed these records for energy and macronutrients.

Self-reported food intake is usually quite unreliable, but if there is one exception, it’s when it’s a competitive bodybuilder doing the reporting. Bodybuilders are notoriously meticulous about everything they put into their mouths.

Nine of the bodybuilders did not carb load in preparation for the contest. The remaining 15 did, the preparation consisting of at least 3 days of depletion (less than 5 grams of carbs per kilogram of body mass and day) followed by a carb intake of at least 8–12 grams per kilogram of body mass and day after weighing in up to the contest itself.

The researchers measured muscle thickness using ultrasound and took circumference and skinfold measurements of the bodybuilders before and after the carb loading (or at the same points in time for the subjects who had chosen not to carb load). In addition, they took silhouette photos of the participants, at the weigh-in and at contest day. Contest judges agreed to evaluate these photos. The judges were blind to the nutritional manipulations of the contestants. Lastly, the bodybuilders self-assessed their mood and gastrointestinal reactions to the carb loading.


The results showed that carb loading improved both physical measurements and visual impression. The judges gave improved photo silhouette scores to the contestants who carb loaded, but not to those who opted out. Both groups reported constipation as a major side effect of the last few days of contest dieting. Seven out of the 15 carb loading athletes reported diarrhea, 4 of them severe. Mood didn’t change depending on carbohydrate intake.

What about muscle thickness? Across the board, the bodybuilders who had carb loaded showed significantly improved muscle thickness everywhere except in the waist area, while the other 9 looked the same the last day leading up to the contest.

This study shows that, if you are planning to enter a bodybuilding contest, carbohydrate loading the last day before getting up on stage might be a good idea if you want to look your fullest and thickest in front of the judges. Just be prepared to experience some stomach problems.

More reading:


Journal of Sports Science and Medicine ( 2019 ) 18, 772-779. Carbohydrate Loading Practice in Bodybuilders: Effects on Muscle Thickness, Photo Silhouette Scores, Mood States and Gastrointestinal Symptoms.

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Andreas Abelsson

Andreas is a certified nutrition coach with over three decades of training experience. He has followed and reported on the research fields of exercise, nutrition, and health for almost as long and is a specialist in metabolic health and nutrition coaching for athletes. Read more about Andreas and StrengthLog by clicking here.