Gut training for athletes - carbohydrates: 6-week protocol to 90g per hour

Training your gut for sports is a physiologically adaptable process. Systematically increasing your carbohydrate intake from 30 to 90g per hour enhances your gut's absorption capacity and prevents stomach discomfort. This protocol achieves that in six weeks. If you first want the complete framework on carbohydrates and endurance sports, read the complete guide to energy bars and endurance sports.

Why can you train your gut for sports?

Your small intestine uses two separate transport channels to move sugars from the intestinal wall into your blood. One channel processes glucose, the other fructose. Both are trainable: the more frequently you stress them during training, the greater their absorption capacity becomes. This is not theory. Jeukendrup described in 2017 how you train your nutrition, systematically increasing your carbohydrate intake during exercise, and thereby enhancing the functional capacity of your gut.

The practical limit for glucose alone is around 60g per hour. The glucose channel becomes saturated. Every gram above that remains in your intestine, draws water, and causes cramps, diarrhea, or bloating. This is the classic stomach problem in endurance sports. The solution is a 2:1 glucose/fructose ratio: two separate routes work in parallel, allowing your total intake to increase to 90g per hour without saturating either route. If you want to know why more and more cyclists are switching to clean carbs, read why cyclists are swapping gels for clean label fruit energy bars.

My fruit performance bar provides precisely that 2:1 ratio in a solid, doseable form. Each bar weighs 25g and provides 20g of carbs, based on 80g of carbohydrates per 100g.

What does the research say about the trade-off at 90g per hour?

Pfeiffer and colleagues (2012) investigated the relationship between carbohydrate intake, performance, and gastrointestinal problems in athletes during actual competitions. The finding was twofold. Higher intake was associated with better performance, but also with more gastrointestinal problems such as nausea in athletes who had not prepared their gut.

The trade-off is clear. 90g per hour provides more fuel, better performance, and spares your internal sugar reserves. But only if your gut is trained. King and colleagues (2019) also confirmed that 90g per hour in a 2:1 ratio is the optimal dose over three hours of exertion, and that more is not better: higher doses impaired performance. Starting untrained at 90g is a sure path to stomach cramps. Starting trained at 90g is an advantage.

What happens if you consume too few carbohydrates?

Cox and colleagues (2010) showed that daily training with sufficient carbohydrates available increases the processing of external carbs. The downside: those who consume too little during intensive exercise deplete their glycogen reserves faster and experience a measurable loss of power. Not because the muscles fail, but because the fuel supply falters. This is the classic "bonk": your internal reserves drop, your blood sugar drops, your output drops.

Under-fueling is at least as problematic as over-fueling. The protocol below solves both: a gradual buildup prevents stomach discomfort and ensures that by week 6 you are actually delivering 90g per hour to your muscles.

What does the 6-week protocol look like?

The protocol is based on the principle that you train your nutrition (Jeukendrup, 2017). Each week you increase your carbohydrate intake during longer sessions. Your gut adapts, its absorption capacity grows, and your tolerance improves. Important: you don't get those carbs from bars alone. The basis is always sports drink, supplemented with 1 to 2 bars per hour.

Use the protocol exclusively during endurance training sessions of at least 90 minutes. Shorter sessions train your gut less effectively, as the exposure is too brief.

Week	Target carbs/hour	Build-up (combination)	Focus
1	30g	Sports drink (6-8%) as base + learn to tolerate 1 bar	Acclimatization to solid food during exercise
2	45g	Sports drink + 1 bar per hour (20g)	Solid food alongside drink, stimulating both channels
3	60g	Sports drink + 1 bar per hour	Reaching glucose limit, 2:1 becomes critical
4	70g	Sports drink + 1 to 2 bars per hour	First exceeding glucose limit, testing fructose route
5	80g	Sports drink + 2 bars per hour	High flux on both routes, consolidating tolerance
6	90g	Sports drink + 2 bars per hour (+ possibly 1 gel in the finale)	Race-specific intake, full gut capacity

Let's do the math for week 6: sports drink provides 50g per hour, two bars provide 40g, totaling 90g. Never three or four bars in an hour, as that overloads one texture and one source. The combination is what works.

What practical rules apply during the protocol?

Gut training only works if you mimic the conditions you expect in a race. Train with the same products, at the same intensity, in the same conditions. Four concrete rules:

• Eat and drink on schedule. Don't wait until you're hungry. Hunger during exercise means you're already behind. Set an alarm. Fuel preventatively.
• Drink water or sports drink with each bar. Carbohydrate absorption requires fluid. Dry intake slows absorption and increases the risk of stomach discomfort. At least 150ml with each bar.
• Never increase two variables at once. Increase either the amount or the intensity. Doing both at the same time masks the cause of any discomfort.
• Note your gastrointestinal complaints per training. Write down: what did you consume, when, at what intensity, what complaints. Patterns become visible, adjustments become targeted.

What role does the 2:1 ratio play?

The 2:1 glucose/fructose ratio is not a marketing claim. It is the functional key above the 60g limit. Glucose and fructose use separate transport channels in your intestinal wall. By stressing both routes simultaneously, you double the effective throughput. With a 2:1 ratio, your processing can increase to about 1.5g per minute, or 90g per hour. If you want to see the difference between drink and solid food clearly, read energy bar vs energy gel: when to use what.

I designed my fruit performance bar precisely on that principle. Each 25g bar provides carbs in the 2:1 ratio, without artificials, without lactose, without gluten. That makes the bar a clean, doseable training instrument. Not as a snack, but as fuel during exercise. The difference between clean and artificial is most sharply seen when you compare a fruit energy bar to classic candy.

How do you know your gut training is working?

After six weeks of consistent protocol, you will notice three concrete changes. First: higher intake without stomach complaints. What felt heavy in week 1 feels normal in week 6. Second: better performance in the last hour of long sessions. Less fatigue, more stable output, the direct result of more available carbohydrates as described by Cox and colleagues (2010). Third: you can refuel faster without feeling full. Your gut is trained to process carbs at pace.

These are measurable, functional improvements. Not a matter of feeling. Performance is the yardstick.

What if you experience stomach problems during the protocol?

Stomach problems are signals, not stop signs. Mild cramps or a full feeling in the first two weeks are normal; your gut is adapting. Severe cramps, diarrhea, or vomiting means you went too fast. Step back to the previous week, consolidate there for two weeks, and then proceed.

Common mistakes: too little fluid with intake, starting at too high intensity (above 75% of your VO2max slows intestinal absorption), switching products in the middle of the protocol, or fueling too close together without fluid. Address one variable at a time per adjustment.

Do you have a sensitive gut? Start week 1 at 20g per hour and extend the protocol to eight weeks. Slower is more sustainable. The end goal remains 90g per hour.

How to use the fruit performance bar in this protocol?

My bars are fuel during exercise. Not a snack. Each bar weighs 25g and provides 20g of carbs in the 2:1 ratio. Vegan, gluten-free, lactose-free, without artificials, made by a certified Belgian production company (BRCGS Food Safety, ACS). This makes them suitable as a solid component alongside your sports drink in this protocol. For a regular training ride, the same logic applies just as well: the ideal fuel for your bike ride.

Practical use per phase, always on top of your sports drink:

• Week 1-2: sports drink as base, 1 bar per hour in addition. Focus on timing and hydration.
• Week 3-4: sports drink + 1 to 2 bars per hour. Gradually increase the amount.
• Week 5-6: sports drink + 2 bars per hour, possibly 1 gel in the finale. Test the exact combination you will use in competition. No new products should be introduced.

No gel. No brick. Fuel.

Training your gut is not a detail. It is the foundation of your race nutrition. Most athletes get stuck at 60g per hour, not because their body can't handle more, but because their gut isn't prepared. That's solvable. Six weeks, a protocol, sports drink as a base, and a clean fruit performance bar with 2:1 carbs as a solid component. No gel. No brick. Fuel during exercise that still hits the spot at hour five. Fuel your flight.

Choose your fuel