Blog Post

Why Are Carbohydrates Important for CrossFit?

CrossFit is a branded fitness program that involves ‘constantly varied functional movements performed at high intensity.’ In a nutshell, the answer to why carbohydrates are so crucial for CrossFit comes down to human physiology and the energy systems predominantly involved in this type of training. 


Carbohydrates are made up of starches, sugars and cellulose. Once digested, they are broken down into single sugar molecules in the form of glucose. This can then be stored in the muscle and liver as glycogen, ready to be used as a quick energy source. 

Examples of carbohydrate-rich foods:

  • Bread, bread rolls, wraps
  • Pasta, rice, quinoa, quinoa, couscous
  • Starchy vegetables e.g. potato, sweet potato
  • Fruit 
  • Jam, honey, sugar

Energy Systems 

Different energy systems of the body prefer different sources of fuel. Human energy systems refer to the specific mechanisms by which energy is produced and used by the body.

We generate energy via three systems:

  • Phosphagen system (ATP-PC)
  • Glycolytic
  • Oxidative 

“The Effect of Exercise Intensity on Fuel Sources” by Allison Calabrese is licensed under CC BY 4.0

Why are Carbs Essential for Optimal Performance in CrossFit?

With CrossFit being a high-intensity style of training, it is predominantly a glycolytic* sport, meaning it will use carbohydrates as its preferred energy source. 

*Glycolytic refers to glycolysis, which is a metabolic process involving the breakdown of carbohydrates. 

Carbohydrates will provide the body with a rapid and efficient energy source. This is because it can be broken down quickly enough by the body to meet the fuel demands of that high-intensity exercise, ultimately supporting optimal performance

Why aren’t Fats the Preferred Fuel Source for CrossFit?

When we eat fat-rich foods (salmon, avocado, nuts, seeds and oils) they are digested and broken down by a process called fat oxidation. During high-intensity activity like CrossFit, the body’s demand for oxygen increases significantly, making oxygen a limited resource. 

Since fat oxidation requires more oxygen compared to carbohydrate metabolism, fats can’t be broken down quickly enough during high-intensity training to meet the immediate energy demands of that exercise.

With a higher fat and lower carbohydrate diet, the power output of a CrossFitter can be negatively affected. Whilst they may still be able to complete high-intensity workouts, the athlete won’t be able to sustain their highest level of intensity for as long as if they had more carbohydrates on board.  

Secondly, quick and powerful muscle contractions often rely on immediate sources of energy like creatine phosphate and carbohydrates. Whereas, fat as a fuel source is largely used for aerobic training and lower-intensity efforts.

It’s important to note, however, that energy systems do not work one system (or fuel source) at a time. They work alongside each other with varying contributions from each system depending on the overall intensity and duration of exercise, i.e. all systems are working at once. 

However, depending on the type of training, there may be a significant portion of energy being generated from one system in particular, e.g. glycolysis (the breakdown of carbohydrates to form energy) during a CrossFit ‘WOD.’ 

So, even though fats are an efficient source of energy (providing a higher yield of energy per gram than carbohydrates), there are limitations to their energy production when it comes to high-intensity training such as CrossFit.

Other Reasons Why Carbs are Beneficial for CrossFit

When carbohydrates are available as a fuel source, the body can spare protein. This means that the body will prioritise using carbohydrates instead of breaking down your muscle tissue for energy during exercise.

Carbohydrates consumed immediately post-workout when training twice within 24 hours can also contribute to a more rapid recovery in between sessions. 

What Do We Recommend for Carbohydrate Intake for CrossFitters? 

All types of carbohydrates play an important role for competitive CrossFit athletes who are looking to optimise their performance. As a rule of thumb, carbohydrate needs increase as an athlete’s training load increases.

It is a good idea to choose higher quality, nutrient-dense options most of the time. However, pre-training we want to improve gut comfortability – a situation when higher sugar products would be more suitable.   

Overall, aim to have a relatively higher carbohydrate diet, including mostly complex (low GI) and nutrient-dense options in your meals. This could look like:

  • Oats for breakfast
  • A wholemeal grain bread sandwich for lunch
  • Brown rice or sweet potato with dinner 

These sources of carbohydrates take longer to digest as they contain mostly starches and fibre.

Having a source of simple (high GI) carbohydrates that are easier to digest pre-training, will mean that you have sufficient fuel on board to train optimally while minimising gut symptoms at higher intensities. For example:

  • Crumpet with honey
  • Fruit bar
  • Juice

These sources of carbohydrates are quicker to digest as they are low in fibre and contain mostly sugars.


  • Carbohydrates are the preferred fuel source for high-intensity training such as CrossFit
  • Having a relatively high carbohydrate diet will support the energy and fuel demands of this sport
  • To optimise performance, ensure that you have enough carbohydrates available in your diet, particularly pre-training
  • As training volume increases, so does carbohydrate requirements
  • Choose a variety of types of carbohydrates specific to the timing of the meal or snack pre or post-workout
By Monica Cvoro

Monica is a supportive dietitian that has a passion for performance-focused nutrition. She enjoys strength & conditioning training and CrossFit. While performance focused nutrition is a strong interest of hers, Monica also loves helping people improve their relationship with food by encouraging people to nourish their bodies with nutritious & delicious food. Qualifications: Bachelor of Science (Nutrition & Metabolism) Masters of Nutrition & Dietetics