Thyroid School, Issue #18// Why TSH Doesn’t Tell the Whole Story

Is your TSH normal but you still feel hypothyroid? Here’s a possible reason why… 

The thyroid hormone receptors in the brain versus those in the peripheral (extremities, organs, etc.) cells use different mechanisms of action to transport thyroid hormones inside the cells. Understanding the role of the brain in overall thyroid health is paramount to appreciating why this matters. Our brain is constantly scanning our body for many things including the available amounts of thyroid hormone. When levels are low, the hypothalamus sends a signal to the pituitary gland to secrete “thyroid stimulating hormone” (TSH). TSH sends a message to the thyroid gland to produce more thyroid hormone. This is why in a true hypothyroid state, TSH is elevated and thyroid hormones (T4, T3) are low.

So, why is my TSH normal, but I still feel crummy? The short and sweet answer is that the way that your brain picks up thyroid hormone versus your cells is totally different. The brain’s thyroid hormone receptors use a process called passive diffusion which means that the hormones transmit into the brain cells without extra energy. Compare this to placing a paper-towel over a spot of water on your countertop— the paper-towel soaks it right up effortlessly. The cells in the periphery, however, use active transport which does require energy. Think of pushing garlic through a garlic press— it requires a little more effort (AKA energy) to do it.

Okay, I keep saying “energy”, but what does that mean? Why should I care? And how does that pertain to nutrition? 

When I say “energy”, I want you to think “calories”. By definition, a calorie is a unit of energy. In nutrition, calories refer to the energy people get from the food and drink they consume. Anytime something in the body is “energy dependent”, this means that it requires caloric contribution to make it happen. When calorie consumption is decreased, whether through intentional dieting and/or uncontrollable food scarcity, the brain is still able to pick up thyroid hormone (remember, it’s not energy dependent), but the peripheral cells’ ability is decreased. Energy production intra-cellularly (inside the cell) is a primary driver in the way you feel and function. Poor cellular energy production = fatigue, slowed metabolism, low motivation, etc. 

To make matters worse, because the brain is still able to get enough thyroid hormone into the receptors, it may be a little late to the game to kick into gear and tell the thyroid to produce more thyroid hormone. This is probably one of the most common reasons that someone may feel worse while dieting, have all the hypothyroid symptoms, but their thyroid looks “normal” (which, by conventional standards means the TSH is “normal”).
Calorie deprivation will have a negative impact on your cells’ ability to transport thyroid hormone inside. Your Basal Metabolic Rate (BMR) is the number of calories your body needs at rest without any additional demand outside of laying down, breathing, and bodily function. Most women need at minimum 1200 calories just to support their BMR— not to mention the increases that come with exercise, movement, digestion, mental activity, etc. It can take time for the basic lab marker TSH to reflect the hypothyroid state because of the different mechanism of action. Transitioning from a deprivation mindset to a nourishment mindset and providing enough calories (energy) to your body is step one of feeling and functioning at your best. Chronic under-eating is detrimental to your thyroid status! 

Get a full thyroid panel to get the full picture of what’s going on. If your TSH is “normal” but you’re experiencing hypothyroid symptoms, you can get an idea of the status of your current thyroid hormones, T4 and T3, by looking at a more expanded thyroid lab analysis. Be sure to get Total and Free T4 and T3— the “free” is what is actually available for use by the cells! 
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