In addition to my previous references to Alan Couzens and Dan Plews, an interesting article from Tim Reed about training 12 / 15h a week instead of 30h :
https://rpgcoaching.com/how-im-going-to-try-to-win-races-on-half-pro-training/


more specifically this part about increasing fat ox with limited training time :


Achieving metabolic flexibility without long training sessions will be tricky as nothing stimulates fat burning like being out there for a bloody long time. The Norwegians, Cam Brown and many other big milage trainers would never be categorised as ever doing low carb sessions, at least from what I hear and read. However, if you’re doing 40 + hours of training a week you’re doing a lot of long sessions, can never replace what you’re burning in carbs and will almost inevitably become a good fat burner regardless of diet.
So how do I improve my now fairly poor fat burning on 12 hours a week training? The answer is an approach I’m not a fan of for athletes doing 25 hours a week plus but tends to work really well on low volume. It includes a lot more carbohydrate deplete/fasted sessions (I can still take in calories from fats and to a lesser degree protein). The goal of training with less muscle glycogen available is it stimulates a greater production of ‘lipase’, the enzyme that mobliises fats for fuel more quickly during shorter duration sessions. The other way I’ll do it is nearly always front loading my training day. Not only does this tend to help with better recovery at night but by pairing more sessions back to back the total duration of that training session will force my body to become more dependent on fats for the fuel the longer it goes on.

This explain why Gustav eat pizza in the morning (35h training per week) while I comfortably perform most of my training fasted (7h to 15h a week) with small carb (natural food, not gel) ingestion if long session (> 2h) ...

I tried only 14/10 intermittent fasting and I felt great. Now I'm going to try 3-day fasting (this article https://betterme.world/articles/fast-for-3-days/ persuaded me to give it a try) but I can't figure out how I should train. Since I am not eating, exercising during such a period may tend to have some health risks. Is it better to take a break in training for these 3 days?

Just go easy. Do you have any reason NOT to just do easy Z1-2 stuff? I’m assuming that you want to stay busy as much as anything, and I think you need to prioritize your goals. Workouts take a back seat to the fast, although I don’t see why they have to be sidelined.

Not speaking from experience here, just seems like “common sense” not to stress about quality higher intensity stuff.

How long does it take to flip this metabolic switch?

I realize it’s silly to think that I’m making much change happen after only 6 days, but it’s exciting nonetheless. I’m currently at 18/6 every day except one this week, and that was 16/8.

I’m also bumping up my run times tomorrow, to 40 min from 30. I feel like I am running “easier” and making decent progress chilling away at my average pace.

Would you please make an appearance at my family Holiday get togethers please?

Listened for hours about how amazing IF is for curing everything from lice to cancer

😂

I have not seen any serious research about multi.day fasting in sport. Maybe some exist.... maybe not.
The only thing I read in serious articles is that after 2 to 5 days (depending on fat ox), you catabolyse your own muscles.... not sure it help.

When you are trying to increase your fat ox with what I call NKATC+LI attitude (Non Ketogenic, Adapted and Timed Carbs + Low Intensity), so in simple words training at low intensity at least 4 hours after ingestion, with well timed and adapted level of carbs, using IF or not (personnally i do IF because it ensure my morning/noon sessions are far from any ingestion), there is no "switch".
There is progressive adaptation.
Moving from low fat ox to high fat ox with this method can take several month, but it is done easily, and in a sustainable way. You can do that for years, hopefully until the end of a long life.

A ketogenic approch (Ketogenic LCHF) far more radical in term of approach (drastic reduction of CHO) and consequences, will make you really "switch" in a few weeks to nutritional ketosis. But this is very different, as you need to be much more carefull in term of health, medical monitoring.... this is a much more "controversial" approach.

So, no switch, but progressive improvments. Patience and regularity :-)

I hear you. Makes sense. I am not trying to reach ketosis in the "keto diet" sense. I'm not changing how I eat although I do feel that I'm making better choices - when you only have 6 hours to eat, I think I tend to not want to waste it on garbage, for the most part.