Skip to content
Shop our Father's Day Gift Guide - click here
Shop our Father's Day Gift Guide - click here
Why Triathletes Need Carbohydrates, Part 1

Why Triathletes Need Carbohydrates, Part 1

For peak athletic performance, triathletes need to consume carbohydrates during training, racing, and throughout the day. Although there has been conversation over the years about endurance athletes eating low carb diets, there is really no way around consuming carbohydrates. Since carbohydrates play such an important role nutritionally, this is a two part article. Part 1 will be about why triathletes specifically need carbohydrates in their training and racing nutrition, while part 2 will focus on carbohydrates in day-to-day nutrition. What you will read in this article are principles that we here at Playtri Coaching have been applying with our athletes for almost 20 years. What you will read works for 99% of all the athletes we coach. (The exception being athletes with underlying medical conditions that require different dietary approaches.)


The human body is an amazing piece of engineering. We put food (plants, animal products, etc.) into our bodies, chew, swallow, our digestive system breaks it down, and uses macronutrients (carbohydrates, fats, proteins) and micronutrients (vitamins and minerals) to fuel, repair, grow, and sustain the body. What we eat becomes a part of our body and what we eat impacts the way our body functions in sport. We need a balance of macronutrients and micronutrients for our bodies to thrive. How balanced our fueling is has a direct impact on the body’s ability to perform in training and racing as endurance athletes. No matter your current training focus it is still important to consume protein, fats, and carbohydrates, because each macronutrient plays a role in training and racing. Generally, protein is for repairing the body in-between our athletic endeavors and fat and carbohydrates are used for fueling. However, the mix of fat and carbohydrates varies based on intensity.


At lower intensity efforts, fat is the primary fuel. This is great news because no matter who you are you have an abundant amount of fat available to fuel low intensity efforts (think long slow runs or bike rides at conversational pace). Even the lightest, leanest marathon runner has approximately 80,000+ calories available for fueling, while their carbohydrate stores have only 1,600-2,500 calories available. At lower intensities, many athletes burn a mix of fat and carbohydrates upwards of 400 calories per hour, while they can burn over 800 calories (mostly carbohydrates) per hour at higher intensities. Now you can see how important carbohydrate consumption is. Even at lower intensities you will run out of carbohydrate stores or “hit the wall” or “bonk” in a workout or race.


If you have ever run out of carbohydrate stores, then you have experienced the physiological equivalent of running out of gas in your car. Your body begins to shut down, it’s hard to turn the legs over, you need to sit and rest and consume some carbs right away. Although you still have enough fat calories available, you cannot continue unless you consume carbohydrates. Under-fueling or not fueling with carbohydrates during your training and racing can have negative impacts on your ability to perform to the best of your abilities.

Additionally, the importance of carbohydrate ingestion becomes more noticeable as the intensity of your efforts increases. Carbohydrates are your body’s quick energy source and as you do harder efforts your body utilizes more carbohydrates than fat until you hit max effort and are burning only carbohydrates.


This is the reason why I like my athletes (particularly 70.3, 140.6, marathon, ultramarathon, gravel cyclists, or RAAM cyclists) to do a Vo2 Calorie Expenditure test  for the bike and run. With this test we can see how efficient your body is at utilizing fat and carbohydrate stores, and then make adjustments in your training to improve that efficiency, and set a race strategy that includes Heart Rate goals and nutrition/hydration goals so you can complete and/or compete at the race distance.


To recap: your body needs all three macronutrients to function properly. However, when it comes to training and racing, carbohydrates reign supreme. Even at lower intensities when your body relies more heavily on fat, your body still utilizes carbohydrates. As intensity increases, your body utilizes more carbohydrates. As the length or intensity of a race or training session increases, you are more likely to “hit the wall.” A Vo2 Calorie Expenditure Test can help you determine your current efficiency and then make adjustments to your training and racing strategies.


In Part 2 of this article we will look at why carbohydrates are important for day-to-day nutrition.

Jim Rowe is a Playtri Level 4 Coach and Coach Education Lead, a USAT LI Certified Coach, and NASM Certified Personal Trainer who works with adult athletes of all abilities from beginners to IRONMAN World Championship qualifiers. Learn more about Jim at

Previous article Gear Recommendations For New Triathletes & Those Who Wants To Excel
Next article Why Triathletes Need Carbohydrates, Part 2