Below is a really nice study by Podlogar and co-authors, looking at exogenous carbohydrate oxidation rates, i.e. how much of the carbs you are eating during exercise are just sitting in your stomach, and how much are used by your body?

While quite a few people are able to tolerate high amounts of carbs (are they really though? I do recall a few elite triathletes throwing up on the course while attempting this feat..), there is very large individual variability in how much we can actually use.

Yep, what you eat, is not what your body can use.

In the study, eating 60 vs 90 grams of carbs per hour resulted in the same rate of utilization.

Pushing things to 100-140g/hour (or more!) because “we can tolerate it”, when the body cannot actually use these carbs, might not be the best way to set us up for success in our next endurance event.

I had this same conversation recently with Dr. Sam Impey, who has also put together a (I believe commercially available) kit to test our exogenous carbohydrate oxidation rates. He’s the one that brought to my attention this issue, when I discussed how I’ve reduced my exogenous carbohydrate intake rates (i.e. having fewer gels) dramatically for marathon pace workouts (see this note here on Substack: substack.com/@marcoalti…)

As it often happens, we need to appreciate individual variability, and we need to test. No point following what’s trendy when it could simply be the best way to sabotage ourselves.

Please don’t confuse what I just wrote with “fewer carbohydrates is better”. Understand individual variability, intake vs oxidation rates, and strive to find what’s optimal for you (or the people that you coach). There are athletes who can oxidize more than the typical recommendations, and there are athletes who can oxidize less. Check out the article to learn more.

Train (and fuel) smart.