Search SAFM

Reverse T3 and the Body Preventing Weight Loss, on Purpose

We have highlighted many times the powerful role that hormones play in controlling weight loss, especially thyroid hormone.  So often when we are trying to support patients with weight loss, we are focused on minor factors and missing the major impact of hormones.

There were many excellent, follow-up questions from practitioners about thyroid labwork and about Reverse T3 (RT3) in particular.  The ubiquitous “TSH alone” labwork approach that many conventional practitioners use can hide many (most!?) thyroid hormone imbalances.  We can instead educate our clients about this potential missed opportunity and recommend they pursue a full thyroid panel, including at least TSH, Free T4, Free T3, TPo and Tg autoantibodies, and Reverse T3.

thyroid-glandFirst of all, let’s bust some myths.  Contrary to many online rants, Reverse T3 is not a “toxic” substance; your body is making it all the time.  The thyroid gland makes primarily T4 thyroid hormone as our metabolic reserve.  Then as needed, peripheral tissues (e.g. liver, kidneys, and small intestines) are converting T4 into RT3 or T3 throughout the day.   T3 drives our metabolism. RT3 is simply how the body gets rid of excess T4 that it doesn’t want to be available for metabolic effects in T3.  If the body wants to promote a higher metabolism, there will be substantially more T3 produced than RT3.  But both are being produced on an ongoing basis.

The issue is when the amount of Reverse T3 overwhelms the body’s supply of available T3 to drive cellular effects.  This is the where the rubber hits the road in terms of stress impairing weight loss.  When a person’s stress hormones are elevated persistently, it influences the our tissues to turn more T4 thyroid hormone into Reverse T3 instead of T3 (which can be unbound or free and available for cellular, metabolic effects).  Reverse T3 uses up available T4, reducing what is available to make T3.  Reverse T3 also fits into cellular receptors making fewer available for T3.   One can have normal – or even optimal – Free T3 and still be suffering from hypothyroid symptoms because of this dynamic.

Of course, each unique client’s symptoms are the most important data.  But if there is a consistent hypothyroid pattern to their experience, it’s not enough to look at RT3 labwork on its own.  Certainly if RT3 on its own is high, that’s a good clue.  One may also find that FT4 is elevated while FT3 is suppressed.  Most importantly, we need to look at the ratio of  FT3 to RT3  (available from the data above).  Given the units with which these markers are often conventionally reported, the ideal ratio is estimated to be 20 or higher (* see note below).  In this case, I recommend one look carefully at the role of this stress dynamic in creating a hypothyroid situation.  (If Total T3 labwork is also available (not often, in my experience), the TT3:RT3 ratio can be assessed too for a value ideally of ~10 or more.)  Additionally, if Free T3 on its own is within the lower half of the reference range, I also recommend thinking about the possible role of insufficient nutrition in preventing higher conversion of T4 to T3 (e.g. iron, selenium, zinc).  I am often asked for mainstream clinical literature on this topic, and this is a great place to start.

High production of RT3 is how the body conserves energy in times of crisis and trauma to ensure our survival is not threatened. Remember always that we have primal mechanisms at play to prioritize surviving over thriving.  If we want the body to allow the thriving implicit in weight loss and a lighter weight maintenance, we have to convince the body that our survival is not being threatened….convince the body that all is well both inside and out.

If we know that the ratio of T3 to RT3 is too low, we can focus on identifying and addressing the root causes of high stress for each unique person.  This is where becoming proficient about identifying the interconnectedness in each unique person’s challenges is critical (and why I have made it a strong focus and particular strength of SAFM programs!).  Sometimes the drivers for sustained, high cortisol are mental/emotional (e.g. ugly divorce, overwhelming work demands).  In my experience, however, there are also always physiological sources of stress at play in those who have sustained high cortisol and have chronically struggled to maintain (or even find) a healthy weight.  I typically discover  one or more of several common causes is at play:  unacknowledged food sensitivities, persistent simmering infections (e.g. viral, fungal), toxicity (e.g. heavy metals such as mercury), use of beta blocker drugs, or an ongoing source of inflammation (e.g. unacknowledged prediabetes) .  We can use therapeutic supplements to provide short-term triage in reducing cortisol (e.g. lowering adaptogenic herbs such as rhodiola, holy basil, and ashwagandha which increase the liver’s metabolism of cortisol). But ultimately, these patients must address the true root cause of their challenges  in order to find lasting relief.

I hope this serves you and your patients and clients!  Your follow-up questions or sharing are welcome.  If you are planning to join us for an upcoming Semester Program, remember you get to choose your clinical courses based on your strongest interests.  I recommend these three clinical course selections as a powerful trio for becoming competent and confident in understanding hormones, including their powerful role in weight loss (or gain):  Reversing Diabetes, Thyroid/Adrenal Myths and Truths, and Hormones Demystified.  For the same reason, these are an excellent choice in particular if your practice focuses on women aged 40-50 as a target market.

With love and gratitude to you for sharing your gifts with the world,

Signature Small




*** Calculating this ratio can be confusing to practitioners and patients alike if “math isn’t your thing”.  If FT3 is measured in pg/dl (e.g. 320), and RT3 is measured in mg/dl (e.g. 15), then the target ratio is indeed 20 or higher.  If FT3 is in pg/ml (e.g. 3.2) and RT3 is still in mg/dl (e.g. 15), the target ratio would be 0.2 or higher.  If you do the math, however, and actually convert the numbers to the same units (as any good scientist will demand!), then the target ratio is actually 0.02.  The geek in me insists on clarifying this to make it fully accurate 🙂  There are all sorts of helpful tools online to help you explore the accurate conversions yourself.

P.S. If you know that healthcare must be transformed to be sustainable and effective, and you believe strongly that Functional Medicine is key to making that happen, we urge you to learn about our semester program.

If you haven’t done so already, sign up to receive weekly clinical tips like this via email, and you’ll also get automatic access to a free mini clinical course.

Like us on Facebook to get more great clinical tips and to get notifications of my next Facebook Live!

10 Questions for “Reverse T3 and the Body Preventing Weight Loss, on Purpose”

  1. 6
    Jacqueline Gang says:

    Can Reverse T3 be too low? Is this indicative of thyroid imbalance?

    Thank you ~Jacki

    • 6.1
      SAFM Team says:

      I am unaware of any negative indications of very low Reverse T3. Keep in mind that this may be simply a downstream result from low levels of T4, which is of course notable and needs attention.

  2. 5
    stefanie Aring says:

    I have a patient I am a bit confused about how to interpret her thyroid data. Here are her labs:

    TSH is 1.269 units/L
    Free T4 is 0.9 ng/dL
    Free T3 is 3.2 pg/mL
    Reverse T3 is 6.2 ng/dL (range is 9-27 ng/dl)

    I think if I did the math right, that makes her Free T3 to Reverse T3 ratio 0.05 pg/mL. Is that correct? And if that is correct, we would say that is optimal, even though the lab reports her Reverse T3 levels are low? I am thinking her free T4 is low, so she is low in reverse T3 because her body is converting her T4 into free T3 instead of reverse T3. Is that also the correct way of thinking about this? I think I believe I know why her Free T4 is low, I am just trying to wrap my head around interpreting the data and making sure I am getting the information down correctly. Thanks for your help!

    • 5.1
      SAFM Team says:

      Yes, the reverse T3 is notably low and the fT3 seems quite ample. We assume you are asking this question because your patient has hypothyroid symptoms, and if so it’s necessary to also consider the role of cortisol and estrogen that will affect the cellular levels/activity of thyroid hormones.

  3. 4
    John Castella says:

    Hi SAFM Team,

    Apologies but I am stuck on the “math”….. ” If FT3 is measured in pg/dl (e.g. 320), and RT3 is measured in mg/dl (e.g. 15), then the target ratio is indeed 20 or higher.”….

    Looking at a FT3 value of 315 pg/dl, and a RT3 value of 20.40 ng/dl, the calculation seems to make sense. But if I convert 20.40 ng/dl to mg/dl = .0000204, the calculation is weird.

    Did I do something wrong here? So sorry if I have missed something and appreciate your patience.

    Thanks, John

    • 4.1
      SAFM Team says:

      No problem, John, and glad to know you figured it out. For all others who may also get ‘stuck on the math’, there is an additional explanation posted at the very bottom of the post, right underneath Tracy’s signature. Please note the three asterisks ***

  4. 3
    Achina Stein says:

    Excellent article Tracy!

  5. 2

    If there is no Free T3 on the labwork, but I have a total T3 and a reverse T3, can you tell me the ratio that can indicate the impact of stress/cortisol on hypothyroidism?

    • 2.1
      SAFM says:

      Given the physiology at play, I believe the ratio involving Free T3 is going to be more helpful, as it will may capture more accurately what is being affected in terms of thyroid *action*. As you know, there are substantially higher levels of T3 in circulation in the blood beyond Free T3, but that which is not Free is bound to binding proteins and thus not able to have cellular effects. My best guidance on this ratio is that ideal is 10 or higher. For example, a nice high Total T3 like 150 ng/dL is not improperly balanced with a nice low level of Reverse T3 such as 15 ng/dL. Just a caution for all of us on this note… Be careful with potential black-and-white thinking; that is, while 10 might be optimal, this doesn’t mean that 11 is “a disaster”. I do think one can accurately say that there is some level of Reverse T3 impact on T3 action in the body – one that will benefit from improving the stability and optimal level of adrenal function. Hope that helps!

  6. 1
    Deborah Beaumont says:

    Really great summary Tracy. I found myself explaining this to a client this morning. Your explanation is more smooth though 🙂

Ask a Question

Practitioner clarification questions are welcome! Please do not post personal case inquiries.