High-Carb Fuelling: When to Use It and How

Most leading research shows that for athletes who engage in endurance sports, consuming up to 90 grams of carbohydrate per hour and maintaining a 2:1 glucose to fructose ratio is ideal for performance. However, this may not always be the case.

We now know that a high-carb fuelling plan of 90 to 130 carb grams per hour can have its benefits, but you must follow certain guidelines if you plan on adopting this approach so you can avoid issues with carb absorption and GI discomfort.

When to Use High-Carb Fuelling

Before you consider implementing a high-carb fuelling strategy, it’s important to ask yourself a few important questions:

• How many calories will you be burning an hour? Is it enough to warrant using a high-carb fuelling strategy?
• Are you racing in hot or humid environments where hydration may be more of a concern?
• What is the length of the race?

With regards to the first question, you are likely burning enough calories. Even if you are working at a relatively low intensity, you’ll likely be using enough of your carbohydrate stores to consider upping your intake. For example, if your average power is over 123 watts, you can benefit from consuming 100 grams of carbs per hour while you’re racing or training. Holding 123 watts per hour burns around 440 kilocalories, which is roughly the equivalent of 100 grams of carbohydrate. If you average over 160 watts, you may benefit from consuming up to 130 grams of carbs per hour while you’re racing or training.

Climate considerations also matter due to dehydration, which will reduce cardiovascular capacity, limit your performance, and also get in the way of gut absorption. High-carb fuelling requires more concentrated (hypertonic) drinks, which slow down the absorption of fluids. This can increase the risk of dehydration. So, if you are racing in an environment that’s humid or hot, sweat loss may happen faster than your ability to replace fluid and electrolytes. If you are training or racing in an environment that’s 26 degrees or over or greater than 75% humidity, your carb consumption should stay at or under 90 grams per hour.

Lastly, it’s important to consider the length of the race. For longer events (6+ hours) you probably won’t be able to replace the fluids you lose over the course of the race. As dehydration becomes more severe this can further restrict gut absorption and cardiovascular performance. High-carb fuelling for events of this kind means you have to strike a balance between sodium, fluid, and carb intake. The safest bet for events like this is to go with 60 to 90 grams of carbs per hour. Push your consumption of carbs as much as possible without restricting fluid absorption caused by highly concentrated drinks.

If the race is less than 2 hours long, your carb consumption can stay towards the lower end of the spectrum, from 30 to 90 grams of carbs per hour. That will be enough to meet your energy requirements and increasing your consumption of carbs is not likely to increase your speed. Generally, a target of over 90 grams of carbs per hour is best suited to events that range between 2 and 6 hours in duration.

How to Use High-Carb Fuelling

Before you target a very high-carb fuelling strategy, make sure you have also addressed the following points:

• Start and stay hydrated. If you have a 2% or greater reduction in body weight due to water loss (ie sweat), you are asking for gut issues and reduced performance. Using a well-rehearsed pre-race fluid and sodium consumption protocol to ensure optimized hydration allows gut absorption rates to begin high, and so hydration does not become a higher priority than carb consumption rate.
• Practice in training. It’s recommended you try high-carb fuelling in your training for by gradually tweaking your consumption upwards from your current tolerable limit during one or two hard sessions per week over a 4-6 week period to improve your gut’s ability to absorb carbs.
• High-carb diet. If you’re not consuming enough carbohydrates in your day-to-day nutrition, your absorption ability will be limited, which means you won’t be able to maximally utilise the carbs that you consume. Sports nutrition experts generally recommend that athletes aim for getting at least 60% of their daily calories from carbohydrate.

When the event comes, you want to follow these guidelines if you’re using a high-carb fuelling strategy:

1. Get started right away and make sure to consume carbohydrates as part of your warm-up.
2. Keep your stomach as full as comfortable. The fuller your stomach is, the faster the gastric emptying rate. Consume frequently; recency of consumption also speeds gastric emptying.
3. Maintain your hydration status. Consuming 500ml to 1 litre of fluid per hour is recommended and usually well-tolerated, and is necessary to allow for maximum carb absorption.
4. Make sure your carbs and fluids include sodium to maximise gut absorption. When there’s sodium, sugar is absorbed more efficiently, so make sure you’re consuming 500 to 1000 mg of it per hour and litre of fluid. The use of sodium citrate will help reduce your beverage osmolarity, which will help to keep your gut comfortable.

When different types of carbohydrates are combined—most commonly glucose and fructose—the rate at which your gut can absorb carbohydrate into the bloodstream is increased by almost 50 percent increase. This is because fructose and glucose use different transporters to absorb into the bloodstream, delivering energy to your muscles quicker. Consuming a mixed carbohydrate sports drink or gel rather than a glucose-only drink allows you to use carbohydrate at a faster rate, and the sugar blend reduces feelings of stomach discomfort. Most sports products will use a mix of carbohydrate sources. Something to note is that even though the 2:1 glucose to fructose ratio is known as the gold standard for maximum carb usage when you’re training, a ratio closer to 1:1 may be better tolerated by some people. We recommend experimenting with different carbohydrate sources and ratios in training to find what works best for you.

Conclusion

So far, there appears to be increasingly solid evidence underpinning the idea that more than 90 grams of carb per hour can be tolerated by some athletes, some of the time, and indications that it may be beneficial to performance. However, consumption of really high levels of carbs must be built up slowly to give your gut time to adapt. It’s also important to recognise that just because carb intakes of greater than 90 grams per hour can sometimes be tolerated, it doesn’t necessarily mean that they should be. Your fuelling strategy should be optimised for you as an athlete and cater to your needs and physiological characteristics. A lower consumption (30-60 grams per hour) may be a more appropriate approach for some people or in specific environments.

If you want to give high-carb fuelling a try to see if you can benefit from this approach, our tips to get the most out of it are to stay hydrated, be on a high-carb diet in and out of training, begin fuelling right away, keep your stomach full, keep your fluid and electrolyte consumption high, and use a combined carbohydrate source in the ratio that works best for you.