Fasting works because it naturally creates a calorie deficit.
Keto works because it removes an entire macro of food, which naturally creates a calorie deficit.
Keto can make fasting easier since you’re already in ketosis amd not yo-yoing back and forth constantly storing and shedding water weight and throwing your electrolytes out of whack.
If you’re no longer losing weight, it’s because you’re eating too many calories.
Experiment and see if something works. No harm as long as you pay attention to your body and stop if things feel off and build up slowly. Keep in mind you’re looking for something -you- can stick with and feel good about so play around
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For me, I’m mostly OMAD (keto) then a couple extended (past 80h) fasts a month. Works for me and makes me feel really good. Certainly doesn’t work for everyone, though