Comment by kudokatz

As an example of this ...

At LT1 (via lactate measurements) at peak 100k fitness with elite economy (n=1) ratios were roughly 23% fat, 77% carb. FATMAX was near 28% at slower speed. This is via training using the now-standard (at elite levels), high-carb approach for fueling ultra marathons.

So many factors--including gut training and fueling--play into this. Most aren't even aware of the details, and the "we don't need no carbs for performance" folks still generally bury their heads in the sand. For performance, we're seeing huge skews to carb-based energy for endurance that were considered "wild" just 5 years ago.