I’ve been on a journey loosing 37kg with the help of intermittent fasting and I went on the road extreme as I usually do. Meaning I was fasting Monday and Thursday and also only eating between 12:00 - 20:00. So basically I did my Tuesday HIIT-sessions without having eaten since Sunday at 20:00. And Thursday sessions without eating since Wednesday 20:00. I didn’t have any problems executing these sessions. But we’re all different and we respond differently. In my case the whole fasting part wasn’t very difficult. However not eating carbs at all would most likely not lead to anything positive. Sorry but endurance sports and keto-diets aren’t friends.