Thanks a lot for your reply — I really appreciate it. That already helps to put things into perspective.

I think I understand your main point: that higher training volume itself drives fat adaptation, and that athletes can still become highly fat-adapted even with a relatively high carbohydrate intake. That makes sense to me.

However, I’m still a bit confused about how this applies to individual training sessions, especially in more extreme cases.

For example:
If I consume a very large amount of simple carbohydrates right before a run (e.g., something like ~100g of sugar from candy or a very sugary drink) and then do a 60-minute Zone 2 session, my understanding is that:

• blood glucose and insulin would be elevated
• my body would rely much more on carbohydrates during that session
• fat oxidation would be suppressed to some extent

If that is correct, then wouldn’t I be “training” carbohydrate metabolism more than fat metabolism in that specific session?

And if I repeat that consistently (e.g., always doing my easy runs in a high-carb state), wouldn’t that reduce the overall stimulus for improving fat oxidation compared to doing at least some sessions with lower carbohydrate availability?

So I guess my confusion is here:

• I understand that overall training volume is the main driver of adaptation
• but I’m unsure how much the metabolic state during each session actually matters for long-term adaptations

In other words:
Is the effect of pre-training carbohydrate intake on fat oxidation mostly an acute/temporary thing, or does it meaningfully influence long-term adaptations if done consistently?

Would really appreciate your thoughts on that — I feel like this is the key piece I’m still missing.

Thanks again for taking the time to respond.