Testing the limits of my (new) metabolism today with 2 hours near marathon intensity on rolling hills, fueling with ~11 grams of carbs per hour.

Yep, no missing zeros there, just eleven grams. Why so little for a hard session?

Now that fat oxidation is quite high (see all the details here: marcoaltini.substack.co…), even near these intensities, I am curious to test an hypothesis I put together following recent research from Andrew Koutnik and others, as well as what we know already about the performance benefits of carbohydrate intake.

In particular, research has shown that performance is not impaired when we provide carbohydrate amounts as low as what is required to avoid hypoglycemia. I think that if I can push fat oxidation quite high and maintain metabolic flexibility (which is what I have done so far by heavily periodizing my diet, without going low-carb all the time), then I can perform at my best with a minimal - as opposed to maximal - dose of carbohydrate.

A certain amount of carbohydrates is a must for performance as it 1) avoids hypoglycemia 2) tricks “brain chemistry”, for lack of better words. With this second point I’m referring to studies showing we can perform better just rinsing with a carb-based solution - a sign that we don’t need them to reach our muscles, but simply to convince the brain there’s availability.

Minimizing carb intake at this point for me is an attempt to find a minimum effective dose that allows me to 1) perform at my best, 2) avoid gastrointenstinal issues and 3) avoid the potential negative long term health implications.

As training is the best time to try new things and test, today I went out with only one gel, for 22 grams of carbohydrates in total. Hence, I had 11 grams per hour, pretty close to the 10 grams per hour that Koutnik and co-authors found to allow their athletes to perform optimally, by avoding hypoglycemia. My take is that avoiding hypoglycemia is only part of the picture, and the brain allows us to do more if we keep a steady (but possibly quite low) flow of carbs coming - especially during higher intensity efforts. The more the better, didn’t work for me.

How did the session go?

Personally, I had not performed this well in almost two years, and I am looking forward to more testing and training in the next months. I might eventually decide to race using a higher rate of carb intake, but understanding the limits of what I can do after improving my metabolism is an interesting part of the process

Happy training!