A side effect of a ketogenic diet has been a nose-dive in my ability to do distance running. Once a week, I try to run 10 or more miles in a single stretch and this week and last I’ve simply not been able to go more than about 8 before I reach a level of discomfort where I don’t want to continue. This isn’t exhaustion or muscle failure but simply not wanting to run any more. So I suppose the alternate explanation is that keto has not reduced my stamina, but turned me into a bitch, albeit a lighter one.