The catch: Most blood tests for thyroid function won't pick up on a dip in T3. That's because they look for T4, the form of thyroid hormone secreted by the thyroid gland, which needs to be converted into T3 to become active. (Study subjects didn't experience a significant change in T4 levels.)
So what does this mean for you? It could help explain why, after an initially successful weight loss, you hit the dreaded plateau, says Francesco Celi, MD, lead study author and an NIH clinical investigator.
But before you think a thyroid medication is the answer, not so fast. “Because T3 levels were still within a low-normal range, we would not consider this a reason for giving people any type of replacement thyroid hormone,” he says. “It’s not clear that it would be helpful in this sort of case, and I am concerned that it could be harmful. Overtreatment with thyroid hormones can suppress normal thyroid function and cause cardiac problems and bone loss.”
So what can you do if your scale has come to a screeching—frustrating—halt? Dr. Celi advises being careful about how much you're really eating (most people underestimate the calories they consume) and building up muscle mass, which will help you burn calories, even at rest. Check out these proven strategies to bust through a weight loss plateau and these metabolism-boosting exercises.
