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Ultimate guide on: Triathlon carbohydrate intake

People metabolize carbohydrates differently. You must find a combination and frequency of intake that works for you.

During a triathlon race, you should consume 1,2 grams of carbohydrates per kilogram of body mass (0,55 grams per pound) each hour of the race. This typically amounts to between 60 – 90 grams of carbohydrates per hour. 

It’s generally not recommended to go above 100 grams per hour. It can cause stomach cramps. If you do go above this threshold, make sure you test it beforehand during training sessions. 

The type of carbohydrate you eat is also essential. The body is only able to absorb 60 grams of glucose every hour. If you need to absorb more than 60 grams (and you usually do), you should mix up the type of carbohydrate you eat. Typically a blend of glucose and fructose is used. Most commonly, you’ll find a ratio of 0.8: or 1:1 of fructose:glucose.

It’s often said that nutrition is the fourth discipline of an Ironman. And you should treat it as such during training. Just as you practice your swimming strokes, you should practice your fueling strategy. We recommend you integrate the fueling plan into your workout. Use the same products you would on race day and test what frequency works for you. 

A quick summary of the article

  1. Consume 1,2g of carbohydrate per kg body mass. Every hour.
  2. You should use mixed carbohydrates. A 1:1 ratio of fructose:glucose is recommended. On the back label of your products, glucose will be described as dextrose or maltodextrin.
  3. You should always test your nutrition strategy in training before a race.
  4. Stay below 80% of Maximal Heart Rate to use the Aerobic metabolism of glucose. This will ensure a steady stream of energy throughout the race.
  5. Use carb-loading to increase your glycogen levels to provide more energy on race day. Gradually increase the number of carbs you eat for five days. Drink water and reduce the number of fibers you eat during the period. 
  6. To properly recover, you should consume 1.1 – 1.5 grams of carbohydrates 30 minutes after your race/training session to refuel your body’s glycogen stores. Your meal should also include protein to further stimulate insulin.

The Importance of Consuming Carbs

When you’re racing at an aerobic pace or high-intensity pace, for that matter, your body will metabolize carbohydrates for energy. 

The carbohydrate you metabolize is glucose. Glucose is what we call simple sugar. As the name indicates, Simple sugars are simple carbohydrate molecules with one (Monosaccharide) or two sugar molecules (disaccharides). Because glucose is a simple molecule, it’s easily broken down and utilized for energy. 

It’s important to understand that glucose isn’t very easily stored due to the simple nature of the molecule structure. Instead, it’s stored as glycogen in the muscles and liver. Glucogen is just a large polysaccharide with several glucose molecules attached. 

During the first minutes of physical exercise, the body uses glucose stored in the blood. These molecules are quickly used up. Then, the body begins breaking down the glycogen molecule to free the glucose. Glucose is oxidized in the muscle cells to produce ATP (Adenosine triphosphate), the body’s main energy source. 

Simply put:

  • Glucose is the fuel.
  • Glucogen is the tank storing the fuel.
  • ATP is the energy (in its purest form) that needs fuel to be produced. 

What carbs you should eat during a race or a training session

Considering that the body uses glucose as fuel, one might conclude that athletes should only consume food, gels, and drinks containing glucose. But this is not correct! Conventionally, this was why, a few years ago, the conventional wisdom was to take a maximum of 60 grams of carbohydrates and not 60 – 90 grams.

Let me explain to you why.

You absorb carbohydrates in the gastrointestinal tract. You can approximately absorb 60 grams of carbohydrates an hour during physical activity. Usually, you need much more than that during a race, especially an Ironman race. 

The gastrointestinal tract can maximally absorb 60grams of glucose every hour. To absorb more than that, it’s possible to mix up the type of carbohydrate. Fructose, for example, uses a different transporter protein which allows it to be absorbed simultaneously.

To conclude: Mixing up the carbohydrate type you use is essential if you need more than 60 grams of carbohydrates an hour. 

A mixture of 1:1 fructose and glucose appears to be the best. If you use any modern gels or sports drinks, this is undoubtedly thought of. But to be sure, always look for fructose and glucose (in the form of dextrose or maltodextrin) on the back label.

Tracking carbohydrate intake

Every athlete’s stomach and metabolism are different. Furthermore, the temperature and humidity in the area you train or the area you plan to race also plays a part in your metabolism. 

Therefore, it’s advised that you track your nutrition consumption in a training journal. Note down what type of nutrition you used, down the detail. 

  1. Total carbohydrate consumption per hour.
  2. Frequency of carbohydrate intake. Did you consume carbs every 20 minutes? Or 100 carbohydrates one time an hour?
  3. What type of carbohydrate did you eat? Primary glucose? Or a 1:1 ratio of fructose and glucose?
  4. And most importantly: How did you feel? Energized? Tired? Did you experience brain fog, or were you clear-minded? 

The best data come to your carbohydrate intake strategy from training sessions as close to race condition you can come. If you plan to compete in an Ironman event, you know that you surely will paddle for +4 hours. Therefore, it’s crucial to base your strategy on data obtained from training rides of +4 hours where your body had the chance to use up the same amount of energy.

Carbohydrate intake during the marathon

Many triathletes rely on fluids such as sports drinks or gels for their carbs during the marathon instead of bars. It’s much easier to digest and much easier for the stomach. 

I always bring a small 650 mL (22 Oz) bottle in a running belt. In the bottle, there is a highly concentrated sports drink. This allows me to take regular sips and therefore give my body a constant flow of carbohydrates. Lionel Sanders, one of the world’s bests triathletes, does this as well. 

But again, this cannot be stressed enough; experiment and figure out what works for you. Training sessions allow the best testing opportunities you’ll need to find what kind of carbohydrate source works for you.

Course nutrition during a triathlon run

During an Ironman race (Or half Ironman race), you’ll typically find Sports drinks, water, gels, and bananas. But you can also bring your own nutrition. 

Carbohydrate intake on the bike

You’ll have to calibrate your carbohydrate strategy depending on how far your race is. Let’s take the Ironman Race as a starting point.

The bike leg of the IRONMAN, or for any triathlon race for that matter, is the longest and offers an excellent opportunity to take in some fuel. Since your heart rate will be lower during this portion of the race, it’s the perfect time to absorb what you need.

You should find what works best for you. But because your heart rate is lower and your stomach works better at this point, you can allow yourself to consume harder-to-digest foods. That could be solids such as energy bars or fruits. It’s essential to stay hydrated and keep your energy levels up. Always wash down solid carbohydrates with water. This will help you digest your food and keep you going strong.

If you eat solid foods during the bike, be sure to consume your last bar at least one hour before transitioning to the run. This allows for gut emptying. The last gel should be consumed 20 minutes before transitioning. Make sure to continue to drink water and sports drink to the end. 

Remember: It is best to eat a combination of carb sources because they are absorbed through different mechanisms and break down into blood glucose at different rates.

Course nutrition during the bike segment

During longer triathlon races, you’ll typically find Sports drinks, Redbull, water, gels, bananas, and bars at aid stations. There will be volunteers handing you everything you need so you don’t have to get off your bike.

Carb loading days before race day

Carbohydrate loading (or carb-loading) is a technique that helps endurance athletes store more glycogen (glucose storage) in their liver, giving them energy for extended periods. By gradually increasing your carbohydrate intake in the days leading up to your event, your body will have more power to draw on when you need it most.

If you want to start carb-loading for a race, you can do so five days before by gradually increasing your carb intake. Then, in the two days leading up to the race, eat lots of carbs to give yourself the best chance of success. The best way to carb-load is by eating carbohydrate-rich foods at every meal and snack. This means bread, pasta, rice, cereal, potatoes, and fruit should be mainstays.

There are a few things you should be aware of when carb-loading:

  1. You’ll gain weight, and that’s good! For every gram of glycogen, you’re storing another 4 grams of water. This simply means your body is better hydrated – and ready for a hard race.
  2. Make sure to drink a lot of water while carb loading. 
  3. During a carb-loading period, make sure to reduce the amount of fiber you’re eating. It will reduce the chance of stomach upset on race day. Chose the white bread over whole wheat.
  4. Do not over-eat or consume too many carbohydrates. You shouldn’t replace everything with carbs for five days. This will indeed be taxing on the GI system. Instead, you should gradually increase the number of carbs during the five days. And make sure to still get greens for vitamins and minerals. 

Carbohydrate intake before the race

Source: wikimedia

The importance of consuming carbohydrates after exercise

During exercise, and especially during a race, your body’s glycogen stores are used op. Consuming carbs will naturally replenish them.

You should consume between 1.1 -1.5 grams of carbohydrates for every kg of body mass (0.5-0.5 grams per pound) within 30 minutes of training. This will refuel your body’s glycogen stores. 

Insulin secretion is better stimulated when protein and carbohydrates are consumed together. Therefore your pre-training or race meal should consist of carbs and proteins. A 3 to 1 ratio of carbs and proteins is recommended. 

What does 60 or 90 grams of carbohydrates look like?

ProductCarbohydrate content
Coca Cola (375ml can)40g
Red Bull (375ml can)37,5g
Most Energy Chews (100g)80g
Most sports drinks (500 ml)~35g
Most energy gels~20-30g
Most energy bars (50g)~35g
Medium banana~25g

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