Keep in mind that just because an advanced athlete has success with something does not mean you can run out and do it today.
I love the concept of metabolic flexibility and the harder and faster you go from one end of the fuel spectrum to the other – the more advanced you need to be to pull it off.
Going from ketosis to higher carbs is about as far from one end to the other as you can go.
It can be done, just do NOT start there. In my experience, most people will never get there nor do they need to be there.
Research has shown (1,2) that those are on a very low carb diet for prolonged periods of time demonstrate a reduced ability to fully use carbs during high intensity exercise, even when glycogen (stored carbs) are back up to par. When you cut carbs to very low levels (under 50 grams per day), the gate keeper enzyme (PDH) to the glycolytic pathways gets altered. Once carbs are brought back in, this enzyme stays altered for some time no allowing full access to the use of carbs, despite their presence.
Start simple and then get as advanced as needed.
1) Burke LM, Angus DJ, Cox GR, Cummings NK, Febbraio MA, Gawthorn K, Hawley JA, Minehan M, Martin DT, Hargreaves M. “Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling.” J Appl Physiol (1985). 2000 Dec;89(6):2413-21
2) Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, Burke LM. “Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration.” Am J Physiol Endocrinol Metab. 2006 Feb;290(2):E380-8. Epub 2005 Sep 27.