gut training: how to train your body to handle more carbs

Cycling performance is not only about how much power you can produce.

It is also about how much fuel you can deliver to the muscles — and how much of that fuel your body can actually handle.

For years, endurance athletes were told to consume relatively modest amounts of carbohydrate during exercise.

Today, things have changed.

90 g/h has become common.
100 g/h is no longer unusual.
And at the highest level, some athletes are training and racing with 120 g/h or more.

But there is a problem.

Your legs might be ready for more carbs before your gut is.

This is where gut training comes in.

Your gut is part of your performance system

When you consume carbohydrates during exercise, they have to pass through the gastrointestinal tract before they can become useful fuel.

The process is not as simple as “eat carbs → produce energy”.

Carbohydrates need to be:

• emptied from the stomach

• digested

• transported across the intestine

• absorbed into circulation

• delivered to the working muscles

• oxidized to produce energy

At low carbohydrate intakes, this process is relatively easy.

But as intake increases, the gastrointestinal tract can become a limiting factor.

Bloating. Nausea. Stomach fullness. Cramps. Diarrhea.

The result is familiar to many endurance athletes:

You have enough energy available — but you cannot physically consume it.

Gut training is the process of progressively exposing the gastrointestinal system to higher carbohydrate intakes during exercise, with the goal of improving tolerance and reducing gastrointestinal problems.

Research has shown that repeated carbohydrate feeding during exercise can reduce gastrointestinal symptoms and carbohydrate malabsorption after a period of training.

In other words:

Your gut can be trained too.

Why can't you simply absorb unlimited carbohydrates?

One of the key pieces of the puzzle is that different carbohydrates use different transport mechanisms in the intestine.

Glucose and glucose-derived carbohydrates such as maltodextrin primarily use the SGLT1 transporter.

Fructose primarily uses GLUT5.

This matters because the transport capacity of a single pathway can become a bottleneck.

If you consume a very large amount of glucose or maltodextrin alone, you can eventually reach the capacity of the main glucose transport pathway.

Some carbohydrate remains in the intestine. Water follows. Fermentation can increase. And gastrointestinal symptoms can appear.

Combining carbohydrates that use different transporters effectively creates another pathway for carbohydrate absorption.

This is the fundamental reason why glucose/fructose combinations can support higher carbohydrate delivery than glucose alone.

Maltodextrin vs glucose vs fructose

Not all carbohydrates behave exactly the same way.

Maltodextrin

Maltodextrin is a glucose polymer.

Although it consists of chains of glucose molecules, it is rapidly digested and ultimately provides glucose for absorption.

It is widely used in sports nutrition because it allows a high carbohydrate concentration without making a drink excessively sweet.

For cyclists, it is particularly useful as the main carbohydrate source in high-carb bottles.

Glucose

Glucose is absorbed primarily through SGLT1.

It is rapidly available and has a well-established role in endurance fueling.

However, relying exclusively on glucose means relying heavily on one intestinal transport pathway.

That becomes increasingly relevant as carbohydrate intake rises.

Fructose

Fructose uses a different intestinal transporter: GLUT5.

This is why adding fructose to glucose or maltodextrin can increase the amount of carbohydrate that can be absorbed and oxidized.

The goal isn't simply to consume more sugar.

The goal is to use different transport pathways to move more carbohydrate through the gut.

The ratio matters

For years, the classic recommendation was approximately:

2:1 glucose/maltodextrin : fructose

For example:

80 g glucose/maltodextrin + 40 g fructose = 120 g/h

This remains a perfectly valid strategy.

But more recent research has increasingly focused on ratios closer to:

1:0.8 glucose/maltodextrin : fructose

At 120 g/h, that would mean approximately:

67 g glucose/maltodextrin + 53 g fructose

Research comparing different ratios has found that around 0.8 parts fructose for every part glucose/maltodextrin can produce high exogenous carbohydrate oxidation and, in some studies, better gastrointestinal tolerance and performance than other ratios.

This does not mean that 1:0.8 is universally superior.

The optimal ratio depends on total carbohydrate intake, concentration, exercise intensity, individual tolerance and the specific athlete.

But it explains why many modern endurance products have moved away from the traditional 2:1 formula.

60 g/h is not the same as 120 g/h

This is where gut training becomes particularly important.

If you currently consume 50–60 g/h, jumping directly to 120 g/h is unlikely to be a good idea.

The target is not simply to force more carbohydrate into the digestive system.

It is to progressively teach the body to process it.

A practical progression could look like:

60 g/h → 70 g/h → 80 g/h → 90 g/h → 100 g/h → 110 g/h → 120 g/h

You don't necessarily need to increase every ride.

Instead, spend several sessions at each level and only progress when the previous intake is comfortable.

The training stimulus should be repeatable.

That means practicing the same strategy during training rather than experimenting with a massive carbohydrate intake for the first time on race day.

Studies using repetitive carbohydrate challenges over approximately two weeks have reported reductions in gastrointestinal symptoms and carbohydrate malabsorption.

Your race nutrition should be trained, not improvised.

120 g/h: the new performance target?

The answer is: sometimes.

Current sports nutrition guidance has historically centered around up to approximately 90 g/h for prolonged endurance exercise when using multiple-transportable carbohydrates.

More recent research is investigating intakes around 120 g/h, particularly in highly trained athletes.

Studies in trained cyclists have demonstrated that 120 g/h of mixed carbohydrate can be tolerated and can increase exogenous carbohydrate oxidation compared with lower intakes.

More recent work has also shown a dose-dependent relationship between carbohydrate intake up to 120 g/h and the preservation of performance-related measures during prolonged cycling.

But there is an important distinction:

120 g/h is a capability, not a requirement.

A two-hour ride does not automatically require 120 g/h.

For many athletes, 60–90 g/h may be entirely appropriate.

The longer and harder the event, the more relevant high carbohydrate availability becomes.

And the higher the intake, the more important gut training becomes.

The real objective: carbohydrate oxidation

There is a difference between consuming carbohydrate and using carbohydrate.

You could theoretically put 120 g of carbohydrate per hour into a bottle.

That does not mean your body will successfully absorb and oxidize all 120 g.

The objective of gut training is therefore not simply to increase the number on your nutrition plan.

It is to improve your ability to:

consume → absorb → tolerate → oxidize

high amounts of carbohydrate during exercise.

This is why the combination of carbohydrate type, concentration, timing and progressive exposure matters.

A recent study in elite marathoners found greater exogenous carbohydrate oxidation at 120 g/h compared with 60 and 90 g/h, reinforcing the idea that trained athletes can utilize progressively larger carbohydrate intakes.

Carbohydrate is now part of the training plan

For a performance-focused cyclist, nutrition should not begin on race morning.

It should be trained alongside the bike.

Think about it in the same way as intervals.

You don't suddenly decide to ride 5 × 10 minutes at threshold after never training above endurance pace.

You build the capacity progressively.

The same principle applies to carbohydrate.

Start with what you tolerate

If you comfortably consume 60 g/h, start there.

Increase progressively

Add approximately 10–15 g/h when your current intake is consistently comfortable.

Practice under realistic conditions

Train your gut during:

• long endurance rides

• high-intensity sessions

• hot conditions

• race simulations

• long climbs

• events where drinking and eating become difficult

Use the same products

If you plan to race with a particular combination of drink, gels and food, train with it.

Your gut needs to become familiar with the actual strategy.

Don't forget concentration and hydration

Carbohydrate intake cannot be considered separately from fluid.

A very concentrated carbohydrate drink can behave differently from the same amount of carbohydrate spread across drinks and gels.

Similarly, consuming large amounts of carbohydrate without enough fluid may increase gastrointestinal discomfort.

There is no single perfect strategy.

Some athletes perform well with a carbohydrate drink.

Others prefer a combination of drink, gels and solid food.

Research suggests that 120 g/h can be tolerated across different delivery formats when using multiple-transportable carbohydrates, including drinks, gels and solid carbohydrate sources.

The best strategy is therefore the one that delivers the required carbohydrate without compromising the gut.

Gut training is another marginal gain

Cyclists spend enormous amounts of money trying to save a few watts.

Aerodynamic equipment. Carbon wheels. Optimized positions. Fast skinsuits. Low-friction drivetrains.

But there is another way to improve performance:

make sure your body can actually use the fuel required to produce those watts.

If your nutrition strategy limits you to 60 g/h while your competitor can comfortably process 100–120 g/h, the difference isn't theoretical.

It becomes particularly important late in a race. When glycogen stores are falling. When intensity increases. When repeated climbs accumulate.

When the final hour becomes a fight between what your legs can produce and what your body can fuel.

Gut training doesn't make your FTP higher. It doesn't make your VO₂max higher. It doesn't make you stronger overnight.

It simply increases your ability to deliver one of the most important performance resources available to an endurance athlete:

carbohydrate.

The takeaway

The next generation of endurance performance isn't only about training harder.

It's about becoming better at using everything you put into the system.

Glucose and maltodextrin provide one major absorption pathway.

Fructose provides another. The right combination can allow substantially higher carbohydrate delivery.

But the gut still needs to adapt. So don't wait until race day. Start at a level you can tolerate. Build progressively. Test different carbohydrate sources. Find your ratio. Train your gut.

Because when you're riding for hours, fuel availability can become just as important as fitness.

Train your legs. Train your engine. And train your gut.