You’ve probably heard 90 grams of carbohydrate per hour talked about in the endurance space as though it is the golden number every athlete should stick to.

The truth is it does vary athlete to athlete. 90g per hour might work for some, but it could be unnecessary for others. Depending on what you are training for, how long you are exercising and what your gut is used to, the right amount may be considerably lower than 90g.

Carbohydrate fuelling works best when the intake matches the demands of the session. So rather than starting with a number, it helps to understand what those carbohydrates are actually doing.

Why carbohydrates matter during exercise.

Carbs are an important fuel source when exercise intensity is high enough that the body needs to make up more energy quickly. We store carbohydrates mainly as glycogen in the muscles and liver, but those stores are limited.

As exercise continues, particularly in an endurance setting, glycogen availability falls. Consuming carbs during prolonged exercise provides another source of fuel, helps maintain blood glucose and can support an athlete’s ability to sustain their intended pace or power output for longer. 

With that in mind, don't make the mistake of thinking every training session needs the support of gels or a carbohydrate drink. For shorter sessions, there is usually enough stored carbohydrate available to get the job done, particularly when the athlete has eaten appropriately beforehand.

The need to fuel during exercise becomes more relevant as duration and intensity increase.

So, how many grams per hour?

Sports nutrition guidelines have traditionally broken carbohydrate intake down roughly according to exercise duration.

Exercise duration	Carbohydrate target
Under 60 min	Usually little or no carbs required during exercise
~1 - 2.5 hours	Around 30-60g per hour
Longer than 2.5 - 3 hours	Up to ~90g per hour

Note: these are starting points rather than flat rules. The commonly used recommendation of up to 90g per hour for prolonged endurance exercise comes from research showing that higher carbohydrate delivery can support performance when exercise continues for several hours.

More carbs isn't automatically better.

Some athletes can be misguided in thinking that if 60g carbs is good and works for them, then surely 90g must be even better. More carbs, more energy, better performance, right? Not exactly, no.

Higher carbohydrate intakes become most valuable when an athlete is exercising long enough, and hard enough, to actually benefit from the additional fuel. Someone heading out for a 75-minute easy run does not have the same requirements as someone going for a 3 hour marathon.

There is also a practical limit to how much carbohydrate the gut can comfortably absorb during exercise. When intake exceeds what you absorb, excess carbs can remain in the intestines and, for a lot of athletes, that contributes to bloating, nausea, cramping or an urgent search for the nearest bathroom.

This is one reason high carb targets should be trained, rather than introduced for the first time on race day.

Where does the 60g per hour limit come from?

Your intestine uses transport proteins to move carbohydrate from the gut into the body. Glucose primarily relies on a transporter called SGLT1, but at higher glucose intakes, this pathway starts to become saturated. Research has shown that a single carbohydrate source such as glucose is generally oxidised at rates around 60g per hour. 

Conversely, fructose uses a different intestinal transporter, GLUT5. By combining glucose and fructose, athletes can use more than one absorption pathway at the same time. This allows carbs to be absorbed and used at rates above what glucose alone can provide, which is why endurance fuelling products often contain a combination of carbohydrate sources.

We go deeper into glucose-to-fructose ratios and why newer formulas are moving away from the traditional 2:1 ratio in another article →

How do you actually take 60 - 90g carbs per hour?

An endurance gel might provide roughly 20 - 30g carbs, while a carbohydrate drink can contribute additional carbs depending on its concentration and serving size.

That means a 60g-per-hour plan might involve, for example, carbohydrate from a combination of drink and gels rather than trying to consume everything from one source. If your drink provides carbohydrate, it needs to be included in the hourly calculation along with gels, chews, food or anything else you are consuming.

This becomes particularly important at higher targets. An athlete aiming for 90g per hour who drinks 30g of carbohydrate and then consumes three 30g gels has actually reached 120g, not 90g. Once again, don't go overboard thinking it will automatically been longer, better performance.

Your race target and your training target don't always need to match.

You probably don't need to fuel every training session exactly like race day. An easy 60-minute run and a three-hour marathon-specific session place very different demands on the body, so fuelling can be adapted alongside your training so that carbohydrate availability better reflects the purpose of the session.

That said, it can be extremely valuable to practise the intended race day nutrition strategy. It gives you an opportunity to test quantities, timing, flavours, fluid intake and tolerance (while there is still time to modify the plan).

What about younger athletes?

Fuelling for younger athletes should take into consideration their development and overall daily nutrition. Sports Dietitians Australia recommends that young athletes adjust carbohydrate intake according to their training demands, with whole foods forming the foundation of their nutrition. Sports drinks and sports foods can play a role during prolonged or vigorous exercise, particularly for competitive athletes, but they do not need to become an everyday replacement for normal food.

Chasing 90g of carbohydrate per hour for a young athlete is unlikely to be an appropriate starting point just because it is common in adult endurance racing. When training volume becomes high, sessions become prolonged, or an adolescent is competing seriously, start at  a lower carbohydrate intake and seek guidance from an Accredited Sports Dietitian.