You can do everything “right” for your gut like cleaning up your diet, taking supplements, doing protocols and working on stress, yet your constipation, bloating, fatigue, brain fog, or bacterial overgrowth keep coming back.
If you’re wondering if you’re missing something, one of the most overlooked missing pieces in gut health is the thyroid, specifically a hormone called Free T3 that many doctors still do not test properly.
The Lab That Refused to Run My Test
I experienced this firsthand recently when I asked my doctor to include Free T3 in my routine bloodwork. He agreed, ordered the panel, and then the lab decided not to run the test because my TSH came back “normal.”
I was shocked. Then angry.
This is exactly how thyroid dysfunction gets missed every day.
If your doctor has told you your thyroid is “fine” based on TSH alone, do not stop there.
TSH is only a signaling hormone. It tells you how the brain is communicating with the thyroid. It does not tell you whether your body is actually producing and converting enough active thyroid hormone to fuel your cells, metabolism, brain, AND digestion.
That is where Free T4 and especially Free T3 become essential.
What Is Free T3 and Why It Matters
Your thyroid produces T4, a storage hormone. Your body then converts T4 into Free T3, which is the active, usable form that drives energy production, metabolism, brain function and gut motility.
Free T3 is the hormone your cells actually use. Without enough of it, everything slows down, including your digestion.
Low Free T3 can cause or worsen:
- Constipation and slow motility
- Bacterial overgrowth in the small intestine (SIBO)
- Bloating and digestive sluggishness
- Brain fog, fatigue and weight gain
- Cold hands and feet, low body temperature
And here’s the crucial part: you can experience all of these symptoms with a perfectly normal TSH. Which means you’ll be told your thyroid is fine, when it’s not! And your gut may suffer as a result.
The Liver-Gut-Thyroid Triangle
The thyroid-gut connection is a loop.
T4 to Free T3 conversion doesn’t happen in the thyroid. It happens primarily in the liver and gut. Which means if either of those systems are struggling, your conversion suffers, regardless of how well your thyroid is producing T4.
A sluggish liver with overloaded detox pathways will block conversion. And a compromised gut lining or imbalanced microbiome will do the same.
Low Free T3 then slows gut motility and creates the perfect conditions for bacterial overgrowth, which further compromises the gut. Worse gut health means lower T3 conversion.
This vicious cycle keeps many stuck:
Poor gut health → impaired T3 conversion → slower motility → worse gut health→ worse T3 conversion
Where the Adrenals Come In
The adrenal glands add another layer to this picture. Chronic stress and elevated cortisol directly suppress T4 to T3 conversion, pushing the body to produce more Reverse T3 (rT3), which blocks the Free T3 receptor.
This means that even with adequate T4, chronic adrenal stress can prevent it from being converted to usable, active thyroid hormone.
The adrenal-thyroid connection is why addressing cortisol balance, through nervous system regulation, blood sugar stability and stress reduction, is foundational for thyroid recovery.
Supporting all three, liver, gut and adrenals opens the door to proper thyroid hormone conversion.
How to Test Properly
First you need to know your actual thyroid levels. Ask your doctor for a full thyroid panel including:
- TSH — the standard marker, but not enough on its own
- Free T4 — how much storage hormone your thyroid is producing
- Free T3 — the active hormone your body actually uses
- Reverse T3 — to see if stress is blocking your Free T3 receptors
- Thyroid antibodies (TPO and TgAb) — to rule out autoimmune thyroid disease
If your physician won’t order the full panel, home blood testing is an option. I offer testing and interpretation to provide a full picture of your thyroid. Plus what to do to improve it.
Reading Your Results
Standard lab ranges for Free T3 run from 2.0 to 4.4 pg/mL, but anything below 2.6 is suboptimal and can produce symptoms even if it falls within “normal” range. Free T3 below 3.0 is worth paying attention to. Free T3 at 2.4 will likely produce symptoms. You won’t feel well and not know why.
You may restrict more food, try another protocol and still be stuck.
How to Support Free T3 Production
If your Free T3 is low, the approach depends on what’s driving it.
If T4 is also low, the thyroid itself may need support. through nutrients like iodine, zinc, selenium and tyrosine, all essential for thyroid hormone production.
If T4 is adequate but Free T3 is low, the conversion process is the problem. That means focusing on:
- Liver support — opening detox pathways through bitter foods, cruciferous vegetables (broccoli sprouts are safe for SIBO), adequate hydration and reducing toxic load
- Gut healing — repairing the gut lining and rebuilding biome diversity to restore the gut’s role in T3 conversion
- Cortisol balance — nervous system regulation, blood sugar stability and adrenal support to reduce Reverse T3 production
- Selenium — one of the most important nutrients for T4 to T3 conversion, found in Brazil nuts and quality animal protein. You can also supplement 200 mg daily.
A note on T3 supplementation: some people supplement Free T3 directly when levels are low. This needs to be supervised by a doctor and dosed very carefully.
Too T3 much can speed up the body, creating excessive heat, sweating, racing heart, anxiety, insomnia or rapid weight loss. It is not something to experiment with casually.
It is always best to help the body convert Free T3 naturally.
The Bigger Picture
The thyroid, gut, liver and adrenals are not separate systems with separate problems. They are an interconnected system that heal together.
If your gut isn’t healing despite your best efforts, getting a complete thyroid picture is an important next step, because when it’s part of the problem, nothing else fully works until it’s addressed.
This is the kind of root cause thinking that drives everything I do in the Brain Body Biome program, where we looking upstream of symptoms, and address the things causing them. Brain, liver, gut, adrenals and thyroid.
Want to get your Free T3 and other thyroid hormones and antibodies tested to get the full picture of your thyroid and metabolic function? Reach out to angelaprivin@yahoo.com to find out how you can test your thyroid yourself, while getting help with interpretation and creating a plan.
