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Comment by PaulDavisThe1st | Hacker News Reader

> could absorb and burn 100 calories per hour

burning a hundred calories an hour is trivial. Most people will burn 100 calories per mile when walking or running, and more if moving as fast as these athletes, and many, many humans can do this for far, far longer than 2 hours.

It's the absorbtion that's the challenge. Maurten is not somehow alone in the particular stuff they've developed - ultra runners are generally shifting up into the 90-120 gram/hr range (or beyond!), using a variety of different companies' products. The gut training protocols for this are widely discussed in the world of running for almost any distance above a half marathon.

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> burning a hundred calories

GP left out the units but is clearly talking about grams ("absorb ... 100 carbs per hour"), not calories (no one needs training to absorb 25g/hr). Carbs are 4 kcal/g. 100g of carb (400 kcal) an hour isn't replacement level for even casual athletic efforts, but it does mitigate the loss of glycogen in muscle somewhat.

Exogenous carbohydrate doesn't spare muscle glycogen, only liver glycogen.

I've read that even if you absorb it all, there's some question about whether it's useful. This Alex Hutchinson article suggests, among other things, that it may spare your fat stores rather than your muscle glycogen:

> Even if you can absorb 120 grams per hour, it might not make you faster. In Podlogar’s study, cyclists burned more exogenous carbs when they consumed 120 rather than 90 grams per hour, but that didn’t reduce their rate of endogenous carb-burning—that is, they were still depleting the glycogen stores in their muscles just as quickly.

https://www.outsideonline.com/health/training-performance/en...

https://archive.ph/Vpk0h

https://pmc.ncbi.nlm.nih.gov/articles/PMC9560939/

That may still be worthwhile if fat is harder to recruit than exogenous carbs.

What does 'harder to recruit' mean though?

Kejelcha is 6'1" and under 130lb.

What fat stores?

It doesn't take much. If an elite burns 1500-2000 kcal running a marathon, even ignoring glycogen and exogenous carb, that's only ~195-260g of body fat (~7.7 kcal/g). Even at an extremely lean 4% body fat, Kejelcha would have 2360g of body fat available. (He's probably in the slightly higher 5-10% range.)

(And obviously, the majority of those 1500-2000 kcal are coming from stored glycogen rather than fat.)

If we're only talking about the marginal difference between 90 and 120 g/hr of exogenous carb, then that's 60g over two hours or 240 kcal -- equating to 31g of stored body fat. That's nothing.

The last few years, cycling and triathlon have been experimenting with upto 120g carbs intake per hour. Last year, Cameron Wurf ate 200g carbs per hour when he broke the world record for fastest bike split ever in a triathlon (which was broken again a few months later).

a 2025 look at elite triathletes fueling at https://www.triathlete.com/nutrition/race-fueling/ironman-wo... shows that norwegian athletes are ingesting higher amounts of carbs (~180g/hr bike, ~120g/hr run - 2 males, ~150g/hr both run & bike - 1 female) especially for the bike portion.

Where does discussion on gut training occur? All I know is you need a 5:4 ratio of glucose to fructose? Then when you train, you use the gels and the more you do it, the more capable your gut gets at absorbing without distress.

Is that all the science to it?

AFAIK 5:4 is just the lowest ratio they've tested. Personally I use table sugar (1:1) and can sustain rates above 100g/h. Haven't hit the ceiling yet, don't really feel the need to explore where that is yet because exceeding the absorption rate comes with the risk of diarrhoea which is bad at any time but especially when you're in the middle of a training session and who knows where the nearest toilet is.

Gut training is consuming large amounts of carbohydrate (preferably in the same form you intend to use when racing), yes.

Eating the same amount of table sugar or of a commercial gel should have pretty much the same effect on performance.

However, for many people eating so much of a very sweet food becomes very unpleasant.

It is very easy and cheap to make at home a gel by boiling in water corn starch mixed with fructose in a microwave oven, for a few minutes. Swallowing such a gel should feel much less sweet than the same amount of a sugar solution.

As far as I know, the only difference between such a gel made at home and the commercial gels for athletes is that in the latter the starch is pre-digested with some bacterial enzyme, so that the long starch molecules are broken into short molecules of dextrine and maltose.

This processing shortens the time until the absorption in the gut, but I am not sure if this is really an advantage in all cases. A slower absorption will maintain an elevated blood glucose level for a longer time after ingestion, which may be preferable if you feed periodically, because it avoids wide fluctuations in the glucose level, while a faster absorption might be useful for an immediate recovery when the glucose level has been severely depleted by not feeding for a long time.

Yes but the science is actually achieving that and finding the limits. It used to be thought that 60g carbs/hour was the limit, then 100g, now it’s thought to be 120g.

It’s also about the methods of achieving that under stress without spewing it all back up. Ironman athletes would stuff their faces on the bike under the assumption that this volume of carb absorption wasn’t possible while running.

Some of the challenge in research will come from competitors not wanting to publish results to maintain an edge. It is mitigated by the visual of the race by (you can see athletes pounding carbs), as well as the nutrition companies wanting to sell more product. This will cause them to publish some information to convince us amateurs to quadruple our purchase volume ;-)

Wow so he was absorbing 400 calories per hour with this gel, but he was likely burning 3-4x that amount (or even more) while running 13.1 miles per hour!

In a two hour race that’s still 800 bonus calories, that’s something.

The race to tolerate lots of carbs is usually something you think of in 8 hour Ironmans. The good part is you can do most of it on the bike, which is much easier to eat as you go. As far as I know, many elite runners were doing like 50% water, 50% sports drink and consuming way under 100g.

> As far as I know, many elite runners were doing like 50% water, 50% sports drink and consuming way under 100g.

This used to be true, and is still true for many athletes up the marathon distance. Above that, however, the momentum has swung heavily to very high carb intake. Most (though not all) of the world's best ultra runners (we're talking 7:00 min/mile pace through mountainous terrain) are picking this up, with many getting to and beyond 100g/hr of carb consumption.

Your body stores roughly 2000 calories in glycogen. They are burning calories but nowhere near the amount a middle pack would be at this pace.

So ~2800 calories of carbs with some fat being burned.

Is there anything here a people who should be dieting could learn here? I’ve found when running, every 3-4km if I do t have sugars/gatorade my blood sugar gets so low I end up almost confused… running suburban streets is tough because I’ve got to cross the road when I’m midly delirious!

How far are you running total, both per run and per week?

Running will absolutely help your health, but on its own it's unlikely to get you thin. It's hard to burn enough to make a big difference without it chewing your body up in other ways - especially if you're overweight and out of condition to begin with, and so a bit more susceptible to injury than skinny runner types.

Thinking of it as a calories in/out equation is counterproductive for most people, if it boosts your cardio health, gets you more active and maybe converts a bit of body fat to leg muscle, that on its own is a win.

Certainly no harm in having a swig of Gatorade every couple of km if it helps you go further, anyhow.

Thanks for your comment!

Unfortunately time hasn’t been on my side for a while now, so my daily running has slipped back to no running in the past year!

I’ll get back at it, but yes… will need to improved diet too

I guess it's the classic case of one not being able to outrun a bad diet.

If fueling during the activity stops you from overeating afterwards and possibly allows you to exercise a bit longer it is worth it, even though it seems counter productive.

> not being able to outrun a bad diet

Dang… I was hoping for some cheat level wisdom :)

What are the long term effects of a lot of processed carbs on the gut?

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