• Lacey Rivette

Fueling for Endurance Athletes: Carbohydrates 101

Updated: May 24, 2020

What are carbohydrates?

Carbohydrates aka "carbs" are the bodies preferred source of energy and includes the sugar, starch and fibers that are found in fruit, vegetables, grains and some milk products. Once eaten, carbs are broken down into the simple sugar molecules glucose, fructose and galactose (more detailed explanation here). These molecules then enter the bloodstream and are either used immediately for energy or are stored in the form of glycogen in the liver and muscle. Blood glucose (or blood sugar) and muscle glycogen serve as the bodies primary energy source during exercise, especially at efforts >75% of VO2 max. The graph below gives a good visual representation of the sources of fuel for exercise at various intensities.

Carbs are also are the macronutrient everyone loves to hate! Seriously though, how many diets, top-selling books, or celebrities have you seen promoting low carb diets? The majority of them boast the benefit of weight loss, but there are even some athletes who claim that fats are the superior fuel source and that a low carb or keto diet can improve athletic performance.

So what's the deal? Are those claims true?

Well, yes and no. While low carb diets can lead to weight loss and are proven to be better at eliciting long-term changes in body weight compared to say, a low fat diet. However, the claims that low carb diets are inherently better for endurance athletes are simply not true. Time and time again the scientific research shows that carbs are crucial for optimizing athletic performance. Furthermore while low carb diets have been shown to elicit favorable physiological adaptations (e.g. improving the bodies ability to burn fat), the research showing those adaptations translate into improved athletic performance is lacking. As is, a practical strategy for implementing this diet into an athletes training regimen without any negative side effects (more on those below). What the research DOES show is that base training (long endurance rides) along with the consumption of adequate carbohydrates promotes similar physiological adaptations and that those changes DO translate into improved athletic performance.

Note: There is growing evidence that multiple training sessions occurring in a single day without consumption of a carb heavy meal in between (which would leave glycogen stores depleted) may elicit beneficial training adaptations without nixing carbs from the diet completely. Again while this is a more practical approach, the long term research on this approach isn't available yet and can't be explicitly recommended.

Enough of my babbling though, clearly I could give an entire TED talk on the research behind this topic. Lets just get straight to the point. Here is a list of just some of the reasons...

Why athletes should include carbohydrates in their diets:

  1. Carbs are the bodies preferred source of energy during exercise.

  2. Carbs are the only source of fuel for intense/anaerobic efforts (VO2 max). Thus, low carb diets limit your ability to do the hard efforts required to drop your opponents, bridge a gap in a race or even just get that KOM/QOM on Strava (cause lets be honest, virtual trophies are important too).

  3. Carbs increase your ability to maintain intense efforts for longer. This is because fats require a higher volume of oxygen to produce the same amount of energy as carbs.

  4. Carbs help reduce recovery time between workouts, allowing athletes to achieve a greater training load. (eating adequate carbs post workout quickly replenishes muscle glycogen stores that are used up during exercise)

  5. Post workout consumption of carbs (along with protein) enhances muscle repair and growth. This is because insulin, an anabolic hormone that is released in response to consuming carbs, acts to increase muscle amino acid uptake and protein synthesis while decreasing protein breakdown.

  6. Low carb diets can lead to muscle loss & impair muscle growth. This is because they limit the types of food you can eat, which typically produces a calorie deficit. As a result, the body turns to burning protein as a source of energy.

  7. Consuming carbs regularly during training can improve gut tolerance of carbohydrates and in turn improve performance during longer events. It also helps you to understand the types and amounts of carbs you can tolerate under different circumstances (e.g. during hard efforts, in warmer weather conditions, or when dehydration has set in).

  8. Carb loading before events lasting >90 minutes improves athletic performance. P.S. did you know carb loading can effectively be done in just 3 days?!

  9. Consuming nutrient dense carbs reduces your risk of getting sick. Yep, low carb diets can compromise immune function.

  10. Diets that include carbs are more sustainable long term, are more affordable and are less likely to lead to nutrient deficiencies.

  11. Carbs increase mental focus. Can you imagine bombing a technical descent without being able to focus? I am not sure about you but I might end up in the ER!

So by now you are probably thinking...

“Okay, okay. I GET IT. Athletes need carbs! But how much do I NEED in order to perform at my best?

Well, here are some charts that are going to help answer that question.

And yes I know it’s obnoxious that this is all in kg, but this is how the recommendations are done and changing it to lbs results in some ugly decimals that are even more obnoxious. The calculation is pretty easy: lbs / 2.2 = kgs.

But to save you from having to do that math, there is kg to lb converter at the bottom of this post or you can just click here for an online converter.

It's important to note that these recommendations are not black and white and your daily needs could be slightly higher or lower than those indicated. For example an athlete who is doing a good amount of VO2 and threshold work will have higher needs per kg than those listed. Another is in the case of female athletes, who naturally have a slightly higher preference for fat as a fuel source during endurance exercise due to sexual differences in body composition and hormonal regulation. Hence, why I noted that females should aim for the lower end of these recommendations.

To give you an idea of how to calculate your needs based on your training load and body composition here is an example:

You can determine how many grams (g) of carbs are in a food by looking at the nutrition facts label (depicted below). Here is a simple example of what an athlete could eat in the first hour after exercise to meet the 64g of carbohydrates required for optimal glycogen replacement.

And for those who have poor appetite immediately after a workout, click here for the link to a smoothie recipe of mine that would be easier on the stomach and still meet those needs!

I hope this has been helpful! Stay tuned for more posts on the fueling needs for endurance athletes including: carbohydrates needs during exercise, the recommendations for protein and fat intake, as well as what a full day of eating for an endurance athlete could look like!


1. Burke, Louise. (2010). Fueling strategies to optimize performance: Training high or training low? Scandinavian Journal of Medicine & Science in Sports. 20 Suppl 2. 48-58.

2. Carbohydrate and fat utilization during rest and physical activity Melzer, Katarina. European e-Journal of Clinical Nutrition and Metabolism, Volume 6, Issue 2, e45 - e52

3. Gibala, Martin. Carbohydrate Availability and Training Adaptation, Exercise and Sport Sciences Reviews: October 2010 - Volume 38 - Issue 4 - p 151

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