One of the things Iām looking into in my own n=1 experience with fasting is where iodine fits in. If youāre supplementing with iodized salt this may be a non-issue for you. My last extended fast, I ended up very cold and feeling crappy, so I ended the fast early, and it appears given some testing I had done that the cold in my case may have been driven by low triiodothyronine (T3), which Iām thinking may have in turn been driven by low iodine. When I fast, I do supplement salt, but neither of the salts that I have on hand at the moment contain iodine, so given that Iād fasted for 5 days, itās possible that I did not have sufficient iodine to allow the thyroid to do its job.
I offer this, not as medical advice, but as my n=1 experience and thoughts on that experience based on the correlation between my symptoms (cold, feeling crappy, and lower HR) and those of hypothyroid.
Once I started eating again, I felt fine, but Iām making it a point to get more iodine in, though as with most things, thereās a sweet spot, and not 100% agreement on exactly where that sweet spot is.
Just another potential piece of the puzzle to consider while fasting.