Bitter asks who actually recommends 150g of carbs an hour
Brady Holmer's durability thread turned into an argument about where the top end of fueling guidance came from in the first place.
The carb number everyone is chasing has a ceiling, and now people in the sport are asking who set the top end at all.
It started with Brady Holmer, who pulled three cycling studies together on durability, meaning how well your physiology holds up as exercise drags on. The headline finding, covered here earlier, was that riders taking 100 grams of carbs an hour saw their time-trial power drop 6.4% after four hours, against 9.3% at 60 grams. Going higher did not keep paying. Moving from 90 to 120 to 150 grams an hour raised how much of the ingested carbohydrate got burned, but exercise capacity did not differ significantly between those doses. All of them beat 10 grams an hour.
eating more, and burning more of what you eat, doesn’t guarantee a larger benefit
Where does 150 come from
Zach Bitter replied with the question that moved the thread along. He asked which experts are writing guidelines in the 150 gram per hour range, noting his understanding that ACSM caps at 90 grams an hour and that ISSN mentions up to 90 plus, with specific delivery recommendations attached.
@LoreofRunning answered that it is the experts who draw up guidelines for elite athletes, then went further and said there is no reasonable evidence behind the number beyond the fact that the best athletes on the planet advise it. The account added that with so many of the best failing to finish at Kona, it may be time to question that.
That is two voices, not a consensus. But it reframes an argument runners have been having all autumn. The conversation has been about how high your gut can be trained to go. The question being asked now is whether the very top of the range was ever built on data or just on what fast people say they do.
What it means for your long run
Nothing in Holmer's thread says carbs do not work. The opposite. Burning through roughly 19% more internal carbohydrate roughly doubled the decline in power at the first ventilatory threshold, and feeding more of it back in preserved late performance. The 100 versus 60 result held even without detectable muscle glycogen sparing, which is to say the benefit showed up in the power numbers without a tidy mechanism to explain it.
As Holmer put it, eating more and burning more of what you eat does not guarantee a larger benefit. For most runners the practical gap is still at the bottom end. A 2025 study flagged by Jonah Rosner found non-elite marathoners averaged 21.7 grams of carbs an hour on race day. The fight over 150 is an elite fight. Almost everyone reading this has room to move before it applies.
no reasonable evidence to support this other than, well, it’s what the best athletes on the planet advise
Which experts are drawing up guidlines in the 150g/hr range?
Win the long run conversation
One email a day. Under three minutes. Marathon results, shoe fights and training arguments, settled.