I have only done a few fast days when I have really restricted my calories to the recommended 500. When I have tried to exercise on these fast days or even the day afterwards I find it really difficult and lacked my usually performance. I went for a simple run and I was so slow, usually I can keep to about 5min per km or less and this run I wasn’t even able to run at 5:15min per km. Does your body take awhile to adjust to be able to exercise when you have no ready carbs to burn?

Exercising in the fasted state preferentially burns visceral fat – hence why it is recommended. They key here is what you eat the rest of the time.. so if you live on “carbs” then exercising fated will be problematic because once you have burned the sugar stored in the liver (as gylcogen) and in muscle, you’ll struggle. But if your background diet is “plant-slant” and healthy (omega-3-rich) fats you’ll find it much easier. Or too put it simply avoid sugar(s) and carbs, especially high-GI carbs.