Holmer finds a carb ceiling, 120 and 150 grams look the same
Zach Bitter asks which experts are actually writing fueling guidelines in the 150 grams an hour range.
Brady Holmer put three recent studies on carbs and durability side by side and came away with a ceiling. More carbs an hour helped, up to a point, and then the numbers stopped moving.
carbs aren't a performance-enhancing drug. They let you use the fitness you've built.
In the first study, cyclists took in either 60 or 100 grams of carbs an hour over a four hour ride, then did a 15 minute time trial. Power dropped 9.3 percent against fresh on 60 grams and 6.4 percent on 100 grams, a gap Holmer puts at about nine extra watts. Glycogen (the carbohydrate stored in your muscles) fell a lot in both groups, with no detectable difference between them.
The second study pushed higher, comparing 90, 120 and 150 grams an hour. Athletes burned more of what they ate, but whole body carb oxidation was identical at 120 and 150, and exercise capacity did not differ significantly. The third study artificially raised how much of the body's own carbohydrate was being used, and the drop in power at the first ventilatory threshold after two hours of riding almost doubled.
What Holmer takes from it
His read is that the usual story, eat more carbs, spare your glycogen, go faster, is incomplete. "carbs aren't a performance-enhancing drug. They let you use the fitness you've built," he wrote. He also suspects the brain is involved, that sensing fuel is available is part of why you can keep pushing.
That lines up with what he has argued earlier, that stacking more grams per hour does not guarantee a bigger payoff.
Bitter questions the 150 gram talk
Zach Bitter pushed on where the very high numbers in the online fueling conversation are coming from. He asked which experts are drawing up guidelines in the 150 grams an hour range, and said his understanding is that ACSM caps at 90 grams an hour and that ISSN mentions up to 90 plus grams an hour with specific delivery recommendations.
What this actually is, is cycling research. The time trial numbers come from riders on bikes, not marathoners at mile 20, and nothing here says 150 grams an hour is harmful. It says the measured gain over 120 did not show up. For a runner who is still working out whether they can hold 60 or 90 grams an hour without stomach trouble, the ceiling argument is a long way off.
Which experts are drawing up guidlines in the 150g/hr range?
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