I’d like to share my experience with a few fasting regimes. For reference, I’m male, 40s, 5’9”, \~135 lb, highly active, average 25,000 steps a day, does body weight strength and running.
This is easy. IMHO, most people can and should do this. I’ve been eating one meal a day for years. Meal time is usually in the afternoon, taking a little over an hour, i.e., fasting time of \~22 hours. I’ve never really felt hungry and achieved my best running performance under this regime.
This is slightly more challenging than OMAD, but I’ve had a few months stretch under this regime with no issues. Same meal time as OMAD, slightly longer duration, \~ 2 hours. The fasting time is \~46 hours. I think most people will have a hard time with this if they follow the typical description on the web, i.e., eat reduced calories on the fasting day. My experience is that when the body is on complete fasting, it does not crave food, but as soon as you eat something, hunger strikes. Now you need to fight the body’s natural instinct and you will fail. That’s why I don’t eat anything on the fasting day. As far as athletics, no issue with endurance. A slight loss of explosiveness on the second day. There were many days when I ran a solothon (solo marathon) the morning of the eating day, i.e., after \~36 hours fasting with no issues. If you want to get into ketosis but fret about what to eat, this regime is guaranteed to work regarless of what you eat. My mouth always has a strong ketone taste on the morning of eating days.
This is more difficult, but still doable. I had a few months stretch under this regime as well. Again, same meal time as OMAD, no longer than OME2D. You can only eat so much in one meal. The fasting time is \~70 hours. You’ll be in deep ketosis for at least two days. Most people shouldn’t be doing this over the long term. I had to stop because I kept losing weight. Even under this regime, the body can still function perfectly fine. A few years ago, I ran a solothon in the morning of each of the three days, i.e., three solothons during fasting. This was around Christmas and I felt perfectly fine afterwards. Under this regime, I do notice that on the eating day, prior to the meal, the body feels colder and needs extra layering.
I don’t do any of these for weight loss because I’m already lean.
As stated above, when I fast, I eat/drink zero calories. I don’t supplement with any salt or electrolyte. I only drink water or tea and only when I’m thirsty, not those arbitrary recommendation of 8 glasses a day. For me, perhaps 4 or 5 glasses max and this is with me exercising daily. Even when I run a solothon, I only drink water when the weather is hot. When it’s cooler, I don’t drink at all. In terms of body weight, for OME2D or OME3D, on the fasting days, I notice the body weight will drop 1-2 pounds from morning to evening, most likely because the body metabolizes glycogen and the bounded water gets released.
You seem rather light, but that could also just be a product of running a lot. How active are you outside of your typical exercise regimes?
How much are you eating per day (even if you aren’t eating per day, I imagine you just scale it up for how many days you go without) roughly in calories?
I know a lot of active people who struggle to do OMAD and get enough food in for the day. I really think healthy bodyweight people, OMAD is the lowest you can go for prolonged/indefinite periods of time.