Body Slows Hormone Conversion

Has anyone heard this before: When you lose a lot of weight--especially if you are hypothyroid--your body's conversion of T-4 to T-3 will slow down to the point that you will no longer lose weight? T-3 is the thyroid hormone primarily responsible for metabolism. This is the response that is responsible for the dreaded plateau. This is the first time I have ever heard an explanation that makes perfect sense to me. What do you think?