05/26/2026
Ever been told your thyroid is “normal”... but you still feel exhausted, foggy, and like your metabolism completely disappeared?
Your thyroid controls how your body uses energy. It affects metabolism, body temperature, brain function, digestion, hair, mood, and more.
Most practices mainly check a lab called **TSH**, which is a signal sent from the brain to the thyroid. But TSH is not the actual thyroid hormone your cells use for energy.
The hormone that does most of the work inside the body is called **T3**.
T3 is the active thyroid hormone that helps your cells produce energy. It helps regulate how efficiently your body burns calories, how warm you feel, how clearly you think, and even how well your muscles and digestion function.
Your thyroid mostly makes a hormone called **T4**, which is like an inactive “storage” hormone. Your body then has to convert T4 into T3 so your cells can actually use it.
The problem? Some people do not convert T4 into T3 efficiently.
So even if your TSH and T4 look “normal,” your cells may still not be getting enough active thyroid hormone to function optimally.
That’s why some people still experience:
✨ fatigue
✨ brain fog
✨ weight gain
✨ hair thinning
✨ constipation
✨ feeling cold
✨ low motivation or low mood
At Prosper Health, we look at the full thyroid picture, including Free T3, because normal labs do not always mean optimal function.
Thyroid hormone regulation of metabolism Authors: Mullur R., Liu Y.Y., Brent G.A. Published in: Physiological Reviews (2014) DOI Link: https://doi.org/10.1152/physrev.00030.2013
