60 Grams an Hour Isn't the Limit Anymore: How Many Carbs Should Age-Groupers Start With?

For years, the textbooks listed 60 grams an hour as the most carbohydrate the human body could absorb.^[1] Now athletes at the level of Kristian Blummenfelt and Mathieu van der Poel routinely take in 90 or 100 grams an hour, and some go as high as 120.

Try those same numbers on an age-grouper, and the usual result is an upset stomach. In bad cases, it all comes right back up. Same 90 grams. Why such a big difference?

It comes down to whether your gut has been trained.

1. Why Does High Intensity Have to Run on Carbs?

Once intensity climbs past lactate threshold, or somewhere around FTP, your body gets much less efficient at burning fat for fuel and leans on glycogen instead. Your glycogen stores are limited, about 400 to 500 grams, and when they run out, you hit the wall.

At high intensity, carbohydrate is your power.

Pros eat more because they burn more, faster. Running the numbers once makes it click:

• Pros: Hold 300 watts for a long time and that's 1080 kJ of mechanical work an hour. Working backward from the 20% to 24% gross efficiency of a human on a bike, total energy cost comes to about 4500 to 5400 kJ, or 1080 to 1290 kcal. If all of that came from carbohydrate, it would mean burning 270 to 320 grams an hour.
• Age-groupers: Using the same math, a rider at 150 watts burns sugar at only about half that rate.

However well you train your gut, you won't absorb 270 grams. The gap can only come out of the 400-some grams of glycogen in your body, and that store keeps shrinking as you burn it. That's also why you can't just copy a pro's fueling plan.

The point of taking in more carbohydrate during a race is to make your stored glycogen last longer, so you still have something left to push with late in the race.

2. How the 60-Gram Limit Was Broken: Two Pathways

The old 60-gram ceiling came from SGLT1, the transporter protein in your gut that carries glucose. It can only handle about 60 grams an hour.^[2] Anything beyond that piles up in your gut, and that's where bloating and osmotic diarrhea come from.

Later, researchers noticed that fructose takes a different route, through a transporter called GLUT5. With both pathways open at once, the oxidation rate of ingested carbohydrate went from around 1 gram per minute with a single sugar source up to 1.75 grams.^[3]

• Glucose pathway: maxes out at about 60 g/h
• Fructose pathway: maxes out at about 30 to 60 g/h

As long as your fueling products use a glucose-plus-fructose blend, you can safely push your total to 90 grams an hour or more. 2:1 was the first ratio to be tested. In a 2008 time-trial study, cyclists drinking a 2:1 mix were 8% faster than cyclists drinking glucose alone.^[4] A lot of products have since moved to 1:0.8. That ratio only wins by a little on oxidation rate, but subjects had noticeably less bloating, stomach cramping, and nausea.^[5]

Can you push it even higher, to 120 grams? A 2022 study compared them head to head. 120 grams an hour (fructose:maltodextrin 0.8:1) did oxidize more ingested carbohydrate than 90 grams (1:2), but the amount of stored glycogen it spared was no different between the two.^[6] Your body being able to do it is one thing. Whether it turns into faster race times is another, and nobody has tested that directly yet.

3. Your Gut Is an Organ You Can Train

"Your gut is an organ that needs training, too."

You'd never wear brand-new running shoes for the first time on marathon day. By the same logic, you can't decide on race morning that today's the day you take in 90 grams. The gut tolerance pros have was built up over years.

Training your gut works on three things:^[7]

• Faster gastric emptying: less of that sloshing discomfort from food sitting in your stomach.
• More transporters: once your body adapts to a high-sugar environment, it makes more carriers, and absorption improves with them.
• Less perceived discomfort: your brain and your gut get used to working hard with something in your stomach.

4. How Age-Groupers Can Build Up, Step by Step

First, how far to go. You don't need to chase 120 grams. Going from 40 to 70 grams an hour is enough to make a real difference in races longer than 3 hours.

Step 1: Figure out how much you're taking in now.

• Pull up the record from your last race or your last long session. Add up the carbs from every gel and sports drink you took in, and divide by the number of hours.
• Most age-groupers who do this find they're only getting 30 to 40 grams an hour, and they thought they were eating a lot.
• Set your target after you've done the math. If you're at 30 grams now, your next stop is 45 to 50. Don't jump straight to 90.

Step 2: Test it in training.

1. Pick products with two sugar sources: the ingredients should include glucose or maltodextrin, plus fructose.
2. Add 10 g/h each week: when your gut starts to feel some pressure, hold there until you've adapted, then keep going up.
3. Always test in sessions with intensity: your gut handles food fine in Zone 1 and Zone 2, and gets worse in Zone 3 and Zone 4. No problems at low intensity doesn't mean no problems on race day.

Step 3: At higher amounts, drink it.

Once you're over 90 grams an hour, chewing solid food the whole way gets hard and tiring. Most pros switch to high-concentration carbohydrate drinks and drink most of their calories. Try swapping "gels only" for "a high-carb drink plus a few gels." It's usually easier on your gut.

Pros can take in more because they practice fueling as part of their training. And most age-groupers aren't eating too much at all. They've been underfueling for years.

That 60 grams is the limit of an untrained gut. You'll only find out where your body's real ceiling is by building up week by week. Before your next race, go back and run the numbers: how many grams an hour did you actually take in last time? Once you can put a number on it, you've got something to train.

References

1. Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 44(Suppl 1), S25–S33. https://doi.org/10.1007/s40279-014-0148-z
2. Jeukendrup, A. E., & Jentjens, R. (2000). Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research. Sports Medicine, 29(6), 407–424. https://doi.org/10.2165/00007256-200029060-00004
3. Jeukendrup, A. E. (2010). Carbohydrate and exercise performance: the role of multiple transportable carbohydrates. Current Opinion in Clinical Nutrition and Metabolic Care, 13(4), 452–457. https://doi.org/10.1097/MCO.0b013e328339de9f
4. Currell, K., & Jeukendrup, A. E. (2008). Superior endurance performance with ingestion of multiple transportable carbohydrates. Medicine & Science in Sports & Exercise, 40(2), 275–281. https://doi.org/10.1249/mss.0b013e31815adf19
5. O'Brien, W. J., & Rowlands, D. S. (2011). Fructose-maltodextrin ratio in a carbohydrate-electrolyte solution differentially affects exogenous carbohydrate oxidation rate, gut comfort, and performance. American Journal of Physiology: Gastrointestinal and Liver Physiology, 300(1), G181–G189. https://doi.org/10.1152/ajpgi.00419.2010
6. Podlogar, T., Bokal, Š., Cirnski, S., & Wallis, G. A. (2022). Increased exogenous but unaltered endogenous carbohydrate oxidation with combined fructose-maltodextrin ingested at 120 g/h versus 90 g/h at different ratios. European Journal of Applied Physiology, 122(11), 2393–2401. https://doi.org/10.1007/s00421-022-05019-w
7. Jeukendrup, A. E. (2017). Training the Gut for Athletes. Sports Medicine, 47(Suppl 1), 101–110. https://doi.org/10.1007/s40279-017-0690-6