Is the low carb-induced T3 decline temporary or permanent?
It’s temporary. As soon as you start eating normal again your t3 level comes back up. However, there is a situation where it can become semi-permanent and that is when you follow a very strict diet and drop a bunch of weight (getting down to a weight your body is uncomfortable maintaining) and then try to maintain it. In that situation your t3 levels won’t rebound until you put some fat back on and get closer to a bf% your body is comfortable with.