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T4, Reverse T3, and Weight Gain with Hypothyroidism

T4, Reverse T3, and Weight Gain with Hypothyroidism

We're talking a lot about thyroid conversion these days… But what does conversion mean? And how does it relate to weight loss?

The truth is, your thyroid hormone conversion is one of THE most important determining factors of your body's metabolism.

But it's often missed by the standard lab testing. That may surprise you. After you read this, you'll understand why it happens and what you can do.

What is Thyroid Conversion?

You rely on your thyroid gland to make thyroid hormones that your body uses for metabolic rate and keeping you healthy… But there's a vital step in this thyroid hormone process where things can go wrong. It's called conversion and here's what many thyroid patients need to know.

Everyday stresses — like chronic fatigue, diet, mineral deficiencies, and toxins — threaten your thyroid hormone conversion. Your body makes T4 thyroid hormone (or you take a medication with T4), then it gets converted into T3. It's T3 that helps you with weight, energy, and endurance and what makes you feel good.

When T4 conversion is working correctly, that is.

Frequently, for thyroid patients it isn't working.

For your thyroid hormone conversion to do its job — and manage your metabolism — your body needs the right foods, minerals, and sleep. Otherwise, you could end up with impaired thyroid conversion.

Unfortunately, it doesn't take much to throw off your conversion and sabotage your metabolism.

You want your thyroid T4 conversion to be working 100%, or you'll continue to experience hypothyroid symptoms, including weight gain. (1)

T4 conversion is an essential process many thyroid patients don't know. If you're someone who eats reasonably healthy and exercises but struggles with weight gain, this conversion issue may be the missing piece of the puzzle.

Learn why you could have a Reverse T3 problem and three ways to improve thyroid conversion.

How Does T4 Conversion Affect Your Metabolism?

Your thyroid gland makes hormones for managing energy and metabolism–mostly, it makes T4 (a storage thyroid hormone), and it makes a little T3 (the active thyroid hormone). You rely on your body to convert that T4 into T3 when you need it.

This process is known as conversion. Here's the problem:

Your body can also turn that T4 into something else, an anti-metabolite called Reverse T3 (rT3). Anti-metabolite means it's working against your T3.

That's right. Reverse T3 blocks your T3 as a built-in mechanism to slow your metabolism and energy production.

Why would your body choose to slow down thyroid function? Your body needs to decide where and how to direct its energy.

For example, if you're sick and your immune system is run-down, it wouldn't make sense for your body to burn excess energy and calories.

Instead, your body would redirect that energy toward rebuilding your immune function and restoring health. It would take energy resources away from calorie burning.

If your body chooses to redirect its energy, it will make more reverse T3 than regular T3. You WILL feel symptoms of hypothyroidism

In addition to sickness, there is a range of issues that can impair your conversion. But first, you may be wondering how you can test for conversion issues.

Is There A Lab Test for Conversion and Reverse T3?

There isn't a test specifically for conversion, but there are a few ways to check for Reverse T3. To start, you will want to get a full thyroid lab panel, which includes: TSH, Free T3, Free T4, Reverse T3, and antibody levels. (4)

Get the Free T3 and Reverse T3 lab tests the same day because their relationship to each other is critical for evaluating thyroid function.  

Ideally, you want your Free T3 levels to be as high as possible (generally upper half to the top end of the "normal" reference range), and you want your Reverse T3 levels to be as low as possible (preferably below 15). 

To calculate your Free T3 to Reverse T3 ratio, divide the Free T3 by Reverse T3. The ideal ratio should be lower than 0.20

A ratio greater than 0.20 indicates too much reverse T3 to Free T3 and means that you could have a conversion issue.

There is an easier way, though less precise way, to find out if you have a thyroid conversion issue. Check your body temperature. If it's consistently low—below 98.5 F. or 36.94 C, but typically lower than 97.8 F. or 36.56 C.— there's a good chance that you have a slow metabolism and you're not converting enough T4 to T3. (2)

What Causes Reverse T3?

Here's where it gets interesting. Whether you have a thyroid, Hashimoto's, thyroid nodules, or no thyroid, the conversion process matters. 

If you've been diagnosed with low thyroid function, your doctor will prescribe a medication–mostly likely one that contains T4 or NDT.

But certain factors can slow down the conversion of T4 into T3, even if you aren't sick, and you may be surprised to learn what they are. 

7 everyday stressors that decrease your T4 to T3 conversion (and slow down your metabolism)

❌ Calorie Restricted diets. Since thyroid patients tend to struggle with weight, it's common to see people restricting their calorie intake. When you cut too many calories, your metabolism will slow down. If you increase your calories, you can regain weight, like in yo-yo dieting. Reverse T3 levels regulate this entire process.

❌ Nutrient deficiencies. Your body may want to convert T4 to T3 but cannot due to mineral, vitamin, and nutrient deficiencies.

❌ Inflammation due to chronic infection, autoimmune disorders, or gut health force your body to convert T4 into Reverse T3. 

❌ Lack of sleep or poor sleep, which can happen due to adrenal cortisol imbalances, increases your Reverse T3 levels. The quality and duration of your sleep are essential for conversion.

❌ Gut health and digestive issues can affect your gut lining and intestinal permeability, which can cause inflammation and compromise thyroid conversion.

❌ Toxins including flame retardants (PBDEs), pesticides (PCBs), Percolate, plastics (BPAs), and Bromine can block thyroid cells and impair conversion. (3)

❌ T4 medication at higher doses can cause conversion issues. Increasing T4 without solving the conversion issues is like putting one foot on your car's gas pedal and the other foot on the brake.

What's even more confusing is the lab testing. If your doctor is only looking at TSH and T4 lab results, increasing T4 medication may look fine on paper because it doesn't show the Reverse T3. In that situation, you might suffer from hypothyroid symptoms, including weight gain, fatigue, cold feet, hair loss, and low body temperature --and not know it. 

If you can address the stressors that cause Reverse T3, you can release the brake on your thyroid hormone conversion and help direct T4 to T3 and start to feel better. 

That's excellent news for your metabolism. If you're eating the right diet, exercising in moderation, and converting optimally, you should find weight loss much more effortless.

3 factors that increase your T4 to T3 conversion (and boost your metabolism)

✔️ Moderate Exercise. Remember, stress can trigger your body to convert more Reverse T3. That includes overdoing it at the gym. Listen to your body and do your best to avoid overexercising.

✔️The Right Diet. Calorie-restricted diets (1500 calories a day or less) may reduce T4 to T3 conversion. Also, unhealthy foods (processed foods, grains, and sugars) can lead to gut health problems and inflammation. Try eating more good quality protein, leafy greens, and healthy fats to help your gut health and conversion.

✔️ Supplements. Certain minerals like zinc and selenium may help your body naturally improve this conversion process. Unfortunately, foods are not a reliable source of selenium because the growing conditions vary greatly. Your liver requires adequate levels of selenium to convert T4. Selenium is also needed to help with inflammation and oxidative stress. I've included the most effective form of selenium in my ThyroConvert supplement, which has helped many people improve thyroid function.

Final Thoughts

As you can see, thyroid hormone conversion is a really important piece of your weight loss goals. When functioning at their best, your thyroid hormones are a metabolic powerhouse. T3 works hard to keep your energy up and helps your body naturally maintain a healthy weight.

Thyroid patients will benefit from understanding the intricate connections between T4 conversion, Reverse T3, T3, and overall healthy metabolism, the more tools, and strategies we have to improve this optimal health foundation.

Learn more about Iodine, thyroid health, and Weight Loss Resistance

Now's the perfect time to stock up on our best-selling Miss Lizzy Thyroid Supplements and support thyroid conversion Shop Now

Are you wondering if you have a conversion issue? Take the quiz and learn more.

Thyroid Symptom Quiz - Miss Lizzy Supplements