I started 16-18 hour intermittent fasting 4x/week about three weeks ago as recommended by Dr Mercola (he recommends daily intermittent fasting however). And my primary care provider is a big advocate of intermittent fasting. I may experiment with Mercola's "keto-fast" protocol once I read his latest book, or maybe not. He also recommends carb cycling, which I just started implementing. I don't consider myself "keto" but do eat much lower carb than I used to eat (usually ^50-150 g/day now , which is more in-line with Primal eating than keto).). Eliminating most grains, vegetable oils & sugar has helped with weight loss, digestive & gastrointestinal issues, knee pain, & has reduced general inflammation. I am currently on Meso 2 of Cathe's STS, alternating with one day of steady state cardio (step, walking, biking), one day of a hiit or interval, and usually one kickbox workout (sometimes substituting lawn work/gardening as it is that time of year ). My rest days are sometimes complete rest, sometimes I include a stretch or short yoga, a walk or low intensity bike ride. I have had no issues with fatigue, nor have I experienced increased appetite that some people say they experienced with STS. The intermittent fasting is pretty easy for me due to having been lower carb for almost two years now & believe my metabolism is very flexible (being able to utilize fat or glucose for energy) as I can workout easily while fasted as long as I'm well hydrated. HTH, Deb