planning a 7 day fast next week, also planning on walking 7-10 miles a day. anyone have experience exercising every day during a long fast?
Yes, I do it daily. My ability to do moderate exercise is much, much higher when fasting (after day 1 usually). This includes light hiking, uphill walking, or cycling in flat terrains. This makes sense: after your body switches to keto, it has a very large energy reserve to draw from (one kg of fat is almost 8000 kcal, which is a good 16 hours of moderate cycling).
However, exercises that require a peak of energy (uphill cycling, running, rowing, etc) are almost impossible for me. This also makes sense: the usual energy source used by your body, glycogen, breaks down extremely fast, while fat takes much longer. The feeling I get when I try these type of exercises during fasts is one of complete exhaustion, like barely being able to walk and having to sit down for a good 15 minutes before moving. This is well-known in the cycling community (they call it bonking). Their solution? Eat a cereal bar or sour patch: heavy in sugar, which is transformed into glycogen extremely fast.
Let me just add something: You have to take additional precautions. Have a good serving of electrolytes before, during and after your exercise, sweating will lead to dehydration, and your body will need even more electrolytes. Another thing is that some people take BCAA before and during the workout, if you buy a keto brand this shouldn’t have any effect in your fast, and I have personally felt much better during and after the exercise when I do take it.