Bill who putters wrote:

There are other issues I'd guess. Care to add or detract. How the
Thyroid helps us handle carbs I'd guess is of great importance.

T3 output drops after two weeks of very low calorie and/or very low carb
dieting. That gives a definite relationship between low carbing and
reduced thyroid output. It's why any good low carb plan only stays very
low for two weeks (with assorted caveats).