Moderate carbs beat extreme fueling
- Sports nutrition guidance still points endurance athletes toward 30–60 g/hour for 1–2.5 hours and 60–90 g/hour for longer events — not a new 40 g/hour rule. - The real hinge is gut tolerance: glucose alone tops out near 60 g/hour, while glucose-fructose mixes can reach 75–90 g/hour, but GI issues rise fast. - That matters because the “90 g/hour standard” is being oversold online; newer reviews push individualized fueling and gut training instead.
Carb fueling for endurance sports is having one of those internet moments where a useful guideline gets flattened into a slogan. The slogan is 90 g/hour. The backlash slogan is closer to 40 g/hour. But the actual science is less dramatic than either camp makes it sound. Basically, moderate carb intake is not “beating” high carb intake across the board. What’s happening is simpler — a lot of athletes perform better on the highest intake they can actually absorb without gut trouble, and that number varies a lot by event, intensity, and practice. Older and newer reviews still land in roughly the same place: around 30–60 g/hour for sessions lasting 1–2.5 hours, and 60–90 g/hour for longer events, especially when intensity stays high. ### Where did 90 g/hour come from? It came from transport limits in the gut. A single carb source like glucose is usually absorbed at about 1 g/minute — roughly 60 g/hour. Add fructose, which uses a different intestinal transporter, and total uptake can climb into the 75–90 g/hour range. That is why high-carb race fueling usually means mixed sugars, not just “eat more gels.” ### So is 40 g/hour wrong? No — but it is not a universal sweet spot either. For many runners and cyclists doing shorter or steadier efforts, 30–60 g/hour is already within guideline range and may feel much better than pushing upward. If an athlete can hold pace, avoid stomach distress, and finish strong at 40–50 g/hour, that is not underfueling by definition. It may just be the right dose for that athlete on that day. ### Why do people struggle with the higher numbers? Because the gut is part of the race. Exercise reduces blood flow to the digestive tract, and concentrated carbs, big boluses, dehydration, heat, and race intensity can all make absorption worse. That is when nausea, bloating, reflux, cramping, and the classic “sloshy stomach” show up. The catch is that a fueling plan only works if it survives contact with your intestines. ### Can athletes train for 90 g/hour? Yes — at least sometimes. Gut-training studies show that repeated carbohydrate exposure during exercise can reduce malabsorption and lower GI discomfort in some athletes. One systematic review found average gut discomfort reductions around 47% in some short protocols, with carbohydrate-feed to elite-race levels. ### What about the flashy 120 g/hour studies? They exist, but they are niche. The best-known examples involve elite trail or mountain runners who had already done nutritional gut training, and the comparisons were usually 60 vs 90 vs 120 g/hour in hard, long events. Those studies are interesting, but they do not mean a recreational marathoner will run better by copying an elite ultra protocol. ### So what should athletes actually do? Match intake to the event, then to your gut. For a hard 90-minute session, moderate intake may be plenty. For a 4-hour race, aiming higher often makes sense — but only if the carb type, concentration, fluid, and feeding pattern are rehearsed in training. Think of 90 g/hour as a ceiling many athletes can work toward, not a floor they are failing to hit. ### What’s the bottom line? The science did not suddenly discover that “less is more.” It keeps saying something more annoying and more useful — carbs help, but the best dose is the most you can reliably use, not the biggest number you can post.
