Why CrossFit Athletes Need Carbs

Why CrossFit Athletes Need Carbs

05 Mar

Why CrossFit Athletes Need Carbs

The athlete and the goal will always dictate the training and nutritional program

Each athlete is unique, and their program and nutrition should reflect that. However to simplify this discussion, we are going to be only looking at those who have aspirations to compete in the sport of CrossFit. We need to look at the tasks and training that go into competing in that sport to dictate what type of fuel sources will serve them best.

The sport of CrossFit includes a wide range of tasks that include but are not limited to: absolute strength lifts, strength speed maxes, extended aerobic power, barbell cycling work at low and high loads, high power glycolytic work, middle zone glycolytic/threshold work, varying muscle endurance contractions, CP-battery contractions to name a few. When looking at these, we see a broad spectrum of energy demands on the athlete.

Defining a CrossFit Athlete

To clarify what we are calling a CrossFit Athlete for the context of this discussion, we define one as someone looking to compete at an elite level in a Sactional Event or the CrossFit Games, who is training at high volume several times per day (see below for an example of the 1st day of a 3 day weekend simulation in preparation for the CrossFit Games and/or Sanctional Event).

Without going down a rabbit hole of what defines high intensity, and how that varies for everyone, it's suffice to say the sport of CrossFit presents tasks that demand ample amounts of energy and output from athletes. Thus CrossFit athletes need specific nourishment to fuel those tasks and recover from them effectively so we can do them again tomorrow.

Carbs are optimal fuel for CrossFit Athletes

Now, what is the most optimal fuel source for the body when output is high? Well, let’s recall biology 101, ATP is the energy currency of the body that drives things like muscle contractions. The faster we can break down and rebuild ATP the more fuel we will have available and for longer periods of time. We can manipulate ATP production by manipulating the fuel or macronutrients (carbohydrates, fats, and proteins) we give our bodies.

In an overly simplified description, looking at only one aspect of fatigue (as there are arguably 9 different components that go into fatigue -- see James FitzGerald’s fatigue model in Mixed Modal), when athletes feel like they need to slow down it's because their muscle tissues are not able to utilize, recycle, and produce enough ATP to sustain the output they are currently demanding on the working muscle tissues. One of the ways we can speed up this process is through optimal fuel intake to ensure we have the supporting pieces to fuel the processes needed to derive energy for the body.

The maximum rate of ATP synthesis, the body’s ability to produce more energy, from fat oxidation (breaking down fat via oxygen) is about 0.40 mol of ATP per minute. In comparison, ATP synthesis from glucose oxidation can generate 1.0-2.0 mol per minute; roughly a 2 to 5-fold difference (1). During CrossFit style training, the rate of ATP synthesized from free fatty acids cannot match the rate of ATP needed to fuel muscular work.

Further, if an athlete became fat-adapted, where the body was preferential to utilizing fat for fuel, there would be a decrease in pyruvate-dehydrogenase activity. This enzyme is the first step in the process of linking the glycolysis metabolic pathway to the citric acid cycle (TAC) which is the step before oxidative phosphorylation (electron transport chain) where we create the largest amount of ATP (30 to 36 ATP’s yielded from 1 glucose molecule). Why is this important? Decreased levels of pyruvate-dehydrogenase will impair rates of glycogen breakdown (2). This will reduce glucose availability to fuel training (3). As Alan Aragon states, “Becoming fat-adapted results in being carb-impaired; it’s not an ideal physiological trade-off” and continues, “This is why low-carb/ketogenic diets can be detrimental to sports that require continuous or intermittent high-intensity efforts” (read: CrossFit).

During CrossFit style training, the rate of ATP synthesized from free fatty acids cannot match the rate of ATP needed to fuel muscular work.

Why Carbs?

Knowing now that carbohydrates are the most preferred and efficient source of fuel for the body for the sport of CrossFit, let’s look at prescriptions around carbohydrate fueling. It’s worth repeating, all training and nutritional prescriptions need to be individualized as everyone is unique and will have differing demands. So, don’t take these as gospel but as general ideas for prescription.

All training and nutritional prescriptions need to be individualized as everyone is unique and will have differing demands.

Before adjusting macronutrient intake, the pieces you always want to be monitoring are: sleep quality and quantity, training quality and results, mood, digestion, arousal, energy throughout the day, bodyweight, and inflammation. These KPI’s (key performance indicators) or Basic Lifestyle Guidelines (BLGs) will ensure the athlete is moving in the right direction and the fuel they are intaking is actually going to make a difference in their athletic performance. 

General Calorie Recommendations for CrossFit Athletes

First, we want to find out what the caloric demands are for the athlete. That will give us an idea of how much food they will need to be intaking, first, before we start to give percentages of macronutrients. Below are the equations Big Dawgs Coaches use (as a starting point) to calculate the calories necessary for athletes depending on their goals:

Very Active Athletes (8-12+ sessions per week)

Calories needed to maintaining bodyweight = BW x 18-20

Calories needed to gain bodyweight = BW x 22-24

Active Athletes (5-8 sessions per week)

Calories needed to maintaining bodyweight = BW x 16-18

Calories needed to gain bodyweight = BW x 20-22

For each athlete, it would be prudent to start on the lower end of caloric intake to see how the body handles that amount of food. From there, if the athlete needs more calories, a titration of calories over a week -7 days- period would be the best approach to avoid excess.

General Carb Recommendations for CrossFit Athletes

When looking at amount of carbohydrate intake per day, this can vary drastically depending on a multitude of factors: how lean are they, how much training are they doing on a weekly basis, how much training are they doing per day, what type of sessions are they doing the most in their week, how old are they, what gender are they, what’s their heritage/background (just to name a few).

All of these questions are going to dictate how much and how well they will handle carbohydrate intake. Let’s remember, we are discussing this with the CrossFit Athlete in mind, who for the most part, will be training twice a day multiple times per week.

45-55+% of daily caloric intake coming from carbohydrates  -or-  Daily Carb Intake = BW x 2-2.4

EX.1) 205# male = 410 grams per day (as a starting point)

EX.2) 150# female = 300 grams per day (as a starting point)

While that may seem high for some people, that’s just a starting point. The athlete mentioned in the beginning of the blog post, is an example of an athlete who would need to be consuming over 300-400g of carbohydrates per day (depending on sex). We would consider this the higher end of the spectrum with regards to training volume and amount of carbohydrates consumed per day.

Worth noting:

“When the period between exercise sessions is less than 8 hours, the athlete should begin carbohydrate intake as soon as practical after the first workout to maximize the effective recovery time between sessions.” (4)

“During longer recovery periods (24 hours), the athlete should organize the pattern timing of carbohydrate-rich meals and snacks according to what is practical and comfortable for their individual situation. There is no difference in glycogen synthesis when liquid or solid forms of carbohydrate are consumed.” (4)

Wrapping Up

We need to understand the goal and the athlete before we start to think about what fueling will be necessary. Once that is known, we can then look at what goes into that sport. With the CrossFit Athlete in mind, we know the sport demands a broad range of metabolic tasks that will require adequate resources to fuel and recover from.

We know from research that ATP synthesized from glucose is roughly a 2 to 5-fold increase in ATP per minute (1-2.0 mol per min) compared to fat oxidation (0.4 mol per min). We know from research that becoming fat-adapted results in being carb-impaired, which becomes a poor physiological trade-off when considering the demands of the sport.

We know the daily caloric demands for these athletes will be higher to promote recovery and growth. By extension, carbohydrate intake will be making up close to half, if not more, than their daily caloric intake.

Before we blindly add more carbohydrates, remember to monitor the major KPI’s or BLGs. These pieces will give direct feedback on how the body is responding to the stress it is imposed and how well it is recovering. This will dictate the direction fuel utilization needs to go for the athlete.

Lastly, everyone is unique and their prescriptions must reflect that.


1: https://www.ncbi.nlm.nih.gov/pubmed/24979615

2: https://www.ncbi.nlm.nih.gov/pubmed/26553488

3: https://www.ncbi.nlm.nih.gov/pubmed/29619799

4: https://www.amazon.com/Food-Nutrition-Sports-Performance-International/dp/0415339073

Additional Sources:

Alan Aragon’s Research Review

Precision Nutrition

Not sure where to start? Contact us about working with a coach. 

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CrossFit® is a registered trademark of CrossFit, Inc. Big Dawgs' uses of the CROSSFIT® mark are not endorsed by nor approved by CrossFit, Inc., and Big Dawgs is in no way affiliated with nor endorsed by CrossFit, Inc.

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