I broke my fast with b-vitamin complex supplement, Omega-3 supplment, liver, ground beef, leafy greens, olive oil, and butter. It seemed to work well enough. I had a bit of a head rush and felt a little bit more lethargic, during digestion. However, I had no real problems with re-feeding. I don't have any means to measure ketones, but I think I have managed to remain in Ketosis after refeeding. However, it is hard to be sure.
Honestly, it was hard for me to notice much benefit to fasting, beyond ketosis and weight loss. I really have no way of directly measuring the effects of autophagy, which is one of the main reasons for my fasting experiment. I currently plan to try a schedule of fasting 5-7 days per month for the next 3 months to see how it goes, but I have no plans for longer-term fasts.
From my past keto-adaptation experience, it takes about 3 weeks of being in ketosis for my endurance to start surpassing my previous levels of endurance. I only have 10 days of keto-adaptation time prior to my climbing trip. Hence the reason why I may need to break out of ketosis, to maximize performance / fun.
If you are a serious athlete, I would definitely recommending benchmarking your performance during the keto adaptation period, to see how long it takes.
I also recommending trying daily intermittent fasting (i.e., 16 hour fast period / 8 hour feeding period). I generally eat two meals from 12:00 to 20:00. My initial impression is that daily intermittent fasting is preferable to multi-day fasting for maintaining and building muscle. I will probably drop the multi-day fasts, once I am no longer working an office job.
I hear you about the lack of noticeable benefits to fasting (can't "See" benefits of autophagy etc.).
The science behind it makes sense in my mind (the articles I've read etc.) so we are going to continue to conduct personal experiments with it.
I will say, fasting for days gave me a tremendous amount of control over cravings/diet/nutrition. I've learned to ignore a desire for something I don't consider healthy (haven't had fast food in months). Moving into the keto realm has made that control even better, reducing desire for carbs/sugar even more.
I don't blame you for breaking a fast or dropping out of keto. We have to LIVE first and our diet/nutrition should support that over all other things. Wife and I are going on a quick trip later this month, things are likely to get UGLY from a nutrition perspective but that's three days, out a month, we'll survive of course.
I wouldn't say I'm a serious athlete but I do run/lift in an endurance methodology (no desire to bulk etc.) on a very regular basis. I am going to start tracking glucose and ketones as I continue my journey (keto blood meter and breath meter on the way....).
***EDIT*** I forgot to add, one thing I'm going to closely monitor is the impact of beer on ketosis. I'll take measurements during the week and prior to consumption, then have beer as usual (A couple on Sunday afternoon, usually when grilling out) and then see how long it takes to get back into ketosis. I can't wait to get the monitors and run several weeks of experiments. ***END EDIT***
I was out on my 12 miler yesterday and I hit a slight wall at mile five/six. Last meal was 15 hours prior. I kind of think it was a "switch-over" and I've gone through this before, start running, feel ok, legs get very HEAVY about an hour in (start fasted, no gels, no sports drink intake) and pace slows, breathing gets labored, keep running and 15-20 minutes later, something happens (endorphins?) and my legs "pick-up" and I can continue the run. The first time I went through this, I was on a 20 miler (similar conditions, fasted, no gels etc...) and it was the biggest ass kicker I've ever had running. At that time I was consuming carbs the day before long runs, I told my wife that I hit the roughest rough patch ever on that run, I almost turned around and went home. I think I ran out of carbs at that point and since I was not re-feeding on the run, I had to swap to body fat stores, which I was not used to.
So, now I'm going to keep carbs very low (except beer on Sundays!) and try to stay in ketosis and see how that works.
I have a crazy idea to maybe do an upcoming 30 miler either fasted or at the end of a 5-7 day fast.... I'm working the plan over in my mind.
I've been doing IF since FEB, that's how I started down this "road". I prefer an appetizer plat between 1600-1800 followed by one "meal" no later than 2000.
I LOVE not taking food to work and "dealing with that". It's not a huge thing but I don't have worry about forgetting lunch at home etc. We don't get antsy about food anymore. Traveling for the day, no issue, we just roll with it and eat whenever we are getting somewhere etc...
Like you, I'm over the monsters/energy shots/etc. We've been slowly reducing sugar all year and that's going to stay low pretty much for the rest of our lives. A little ice cream on Christmas Eve maybe and other major holidays and that's going to be about it for us. The rest of the time we plan to use replacement strategies.
Wife and I were chatting this weekend and the hardest thing about something like this is that you are working to overcome (in our case) 35+ years of diet/eating/nutrition habits since most of them form from a very young age. It takes that long for them to form, it takes a lot of effort to overcome them and put new habits into place.
For instance, growing up we drank sweet tea in my house, when we first got married, we started drinking sweet tea, just because. Once we thought about it, we switched to other drinks (this was YEARS ago). It took some time to get used to not drinking sweet tea but we eventually "got over it" and moved on. A glass of sweat tea today would put me on my ass from the sugar crash. I don't plan to go "back" to monsters either (one of those things that sneak up on my in times of stress/lack of sleep/lack of alternatives), your example being yet another great reason for that.