re: Study: fasting results in complex metabolic changes

For an expanded science-based view of both fasted and keto diets and endurance training take a look at these videos from Dylan Johnson who is a cycling coach:

Fasted training

Keto training

Anecdotally I have tried both this year since due to COVID there are no races so I didn't have anything to screw up, if nothing else it has been a good time for my wife and I to try different approaches without any real repercussions.

Neither of them work for us, we are both demonstrably slower fasted and in ketosis. Fasted my body was screaming for carbs within 30 minutes and it was clear my glycogen stores were tapped out. The Keto diet left me feeling sluggish an bloated after 45mins to an hour and I could feel the oxygen deficit I was paying to digest the fats. I did feel better in intervals but overall FTP and anaerobic efforts still suffered both in max power and speed.


For context I am 53yo 6' 170 low body fat and race at ~162 with a FTP of just over 4 watts per kilo. So I am not interested in losing weight. I also average 16 hours on the bike a week and my daily intake is roughly 4000 calories mostly meat and white/beige carbs. I found fasting the worst of the two for me. Keto didn't impact my power as much but it was a PITA compared to my normal diet and fasting just made eating a chore to get in the calories inside the window. My experience has no bearing on their use for weight lose since it wasn't my goal, I did drop 4 quick pounds of water weight as expected with keto. Both took a week to 10 days before my power numbers normalized after I resumed my normal diet. My wife saw similar impacts but was less patient than me, pretty quickly saying frick it when her power dropped and went back to our normal diet.