Seriously though, I did a 5 day fast last week after doing a ton of research/reading about them as regards longevity/improving metabolism/health/etc... Felt great. Wasn't hungry at all, never light-headed, felt I could have gone a lot longer. Worked out as usual and felt as strong, but my stamina definitely took a dip. My fasting blood glucose has averaged 76 b/c keto since January 1st, and it only dropped to 65 during the fast. My ketones, however, skyrocketed -- which is what's supposed to happen when you're not eating while in ketosis. All in all it was a pretty interesting experience.