I’ll see this idea that fasting and keto are bad for thyroid occasionally in ray peat circles. Peaters as a whole have some decent health takes. I’ve not had any thyroid issues that I can tell, but I also don’t get it tested and FWIU thyroid is a bit tricky in general as we don’t know a bunch about it.
I’m not sure it will answer your question but from a study on mice I’ve found, water restriction (without food restriction though) tended to increase T3. I believe you won’t be anabolic if you restrict calories too much in all cases.
I also think that there is more to metabolism control than just thyroid hormones, for example, the Liver X receptor might increase the uptake of iodine in the cells and oxytocin could also control thermogenesis.
I’m hoping to fix mine. I just finished my first dry fast, I was determined to make 24hrs, hopeful of making 36, and then after 36 set my sights on 48 or 60, I took water at 44hrs but haven’t had anything else yet.
I’m sure I’ll have to do much longer fasts to be helpful… I really wasn’t prepared for how bad I would feel, but at the same time went into it fighting a head cold. Next time i hope for 48 minimum, 84 hopefully. I won’t take my T4 meds.. see how it goes.