Found it. This post highlights why for long rides you need to have robust fat metabolism. Awesome post by the way - thanks @konradkowara for sharing.
I love the TR product and podcast, but this is something I think the TR crew have not given enough credence to. A sugar and carb approach is great for 1-2 hour rides, and absolutely should carb load and eat during long rides, but to make it through long rides, you need robust fat metabolism. And the ways to train this don’t always align with just getting the highest FTP.
Take a look at the 2017 vs 2018 fat vs carb profiles for the person who posted this. It’s very telling. Imagine trying to do the LT100 with a profile like the 2018 one.