The Thyroid and Weight Loss

If you are worried about your thyroid, think it may be causing you to gain weight or have noticed your thyroid numbers changing as you lose weight this post is for you! In addition to weight gain and stalled weight loss low thyroid hormone levels known as hypothyroidism can cause you to suffer from feelings of cold, constipation, brain fog (memory or concentration issues), fatigue and lack of motivation among many other things!

You may also notice excessive sleep, feelings of or actual clinical depression, hair loss, mood swings or dry skin. In short when you do not have enough thyroid hormone you feel terrible. If this sounds like you, know you are NOT alone!

Thyroid dysfunction is estimated to affect up to 15% of the population at some point in their lifetime. Women are up to 8 times more likely to be affected than men and the numbers go up as you age. While that is a lot of people some estimate that over half of those with thyroid dysfunction do not know they have it! Incredibly, Thyroxine, the most frequently used medication to treat hypothyroidism is already one of the most frequently prescribed medications in the country.

So, why so much thyroid dysfunction? Is the thyroid the true culprit for our obesity epidemic? Or is it the victim? To understand the relationship between the thyroid and weight loss we must understand a few basics.

The thyroid gland is in the lower front end of the neck and produces thyroid hormones. These hormones are responsible for communicating with nearly EVERY CELL of your body and they regulate the speed of all the biologic machinery that makes you function.

Thyroid hormone is involved in multiple systems and utilizes sensitive feedback loops to up and down regulate cellular metabolism based on perceived inputs from your body, the food and water we provide it and the environment around us.

Unfortunately, with a plague of chronic stress, nutritionally depleted food sources, contaminated water and frequently toxic environments our thyroid may not be functioning how we would like it to! To optimize this gland and its hormones we need to know a few basic terms.

While there are many hormones that play a role in the production of or suppression of thyroid function the hormones directly involved include Thyroid Secreting Hormone (TSH), T4, and T3. The latter two can also be measures of Free T4, Free T3 and Reverse T3. TSH is the hormone that stimulates secretion of thyroid hormone.

TSH is secreted from the pituitary gland at the base of your brain. TSH levels are the most frequently and erroneously sometimes the only test obtained to look at thyroid function. TSH levels can remain within “range” despite significant thyroid dysfunction and sometimes look off despite normal function, particularly when recovering from obesity.

The measurable thyroid hormones (T4, T3, Free T4, Free T3, Reverse T3) and antibodies to look for an autoimmune cause of dysfunction should all be ordered. Even if the correct tests are run only a partial picture of the thyroid state of being can be revealed.

There are myriad additional labs that could be ordered to help complete the picture including sex hormones and nutrition labs but even with all this information some aspects of thyroid function are not fully known and the interaction with food and energy consumption is one of them. To understand each individual situation the symptoms, labs and history must be considered.

To understand if we should be worried about your thyroid numbers to begin with, we need to know the relationship between obesity and the thyroid. Research universally shows that obesity is associated with elevated TSH and thyroid hormone levels. That is NOT to say that thyroid abnormality caused the obesity. In fact, it seems to be the opposite.

TSH, T4 and T3 hormone levels generally increase with weight gain. T4 and T3 levels will come back to normal levels after weight loss but TSH frequently stays elevated. These associations demonstrate the impact that weight gain has on our hormonal axis and the lasting effects that even a single episode of weight gain can leave behind.

This is part of the metabolic dysfunction that results in more difficulty with weight loss as time goes on and why getting to your optimal weight and staying there is so critical.

So, what happens when you lose weight and does weight loss cause hypothyroidism? There are multiple avenues to explore in this question. First, yes, your hormone levels will drop with weight loss. Sometimes this can be completely explained by the association of obesity with higher hormone levels to begin with and the “normalization” of some of your thyroid hormone levels with successfully achieving optimal body alignment.

Reduction in hormone levels could merely represent your body coming back to homeostasis. However, weight loss can result in worsening thyroid function to varying degrees depending on two factors worth considering. The extent of calorie restriction and dietary fat sources appear to play the largest roles in determining the deleterious effects of weight loss on your thyroid. Choosing the right approach can separate weight loss and maintenance successes from failure. Let us look at the science behind both of these factors.

Severe Calorie Restriction:

A classic approach from the medical community to lose weight and the epitome of “eat less and move more” is to simply reduce calorie consumption. I have written on the flawed science behind this approach before but when viewed through the lens of the thyroid we see another reason to turn your back on this solution to obesity.

Severe calorie restriction diets result in a significant reduction of circulating T3 (the active thyroid hormone). Even modest calorie restriction demonstrates a reduction in T3 that gets worse as the rate of weight loss increases. In other words, the more successful people were with calorie restriction the worse their thyroid hormones looked.

The body perceives this deprivation as a threat and stops converting T4 (circulating storage) to T3 (active hormone) and converts it to rT3 a non-active form which is rarely measured. The rT3 conversion explains why most studies show no change in TSH or T4 levels. Some aspects of the thyroid panel look like they are working great but thyroid hormone is not getting to the cells as it’s supposed to!

You may feel like and look like you have hypothyroidism but if your doctor only runs TSH and T4 they will likely look normal. This leads to frustration and frequently failure of willpower in the current diet approach and ultimately weight regain. To make matters even worse if calorie restriction is combined with unhealthy dietary fat your thyroid function can get even worse.

As PHD clients you are told to eat “healthy fats” and given wonderful advice on where to find them. Unfortunately, we live in the minority with our dietary fat understanding. Viewing thyroid function through the lens of dietary fat sources gives us another reason to pursue the best dietary fat possible! In this study that used exclusively corn oil as a fat source we see the same changes in thyroid hormone that we see with severe calorie restriction.

Corn oil is >60% Polyunsaturated Fatty Acids (PUFA) and specifically high in Linoleic Acid (LA). Soybean Oil (>55% LA) and Safflower Oil (>70% LA), both common dietary fats in processed foods have been shown in rat models to reduce the activity of T3. So, even if you can keep your levels elevated if you consume unhealthy dietary fat you may still feel like you are hypothyroid. Functionally at the cellular level, you are. Conversely in animal models using dietary fat sources high in omega 3 PUFA (fish oil) T3 activity was increased across multiple receptors.

In this human study people ate 61% of their calories from dietary fat. 50% of total calories from saturated fat (SF) and monounsaturated fats (MUFA) and only 11% from PUFA. These subjects did not restrict calories and ate to satiation. While still losing weight the saw subtle increases in T4 levels but no change in T3 function. Amazingly, they also gained lean muscle mass over the 6-week trial.

While these results are promising not every study shows the same results. Unfortunately, for many reasons, most well-funded studies on weight loss without calorie restriction that include some component of carbohydrate restriction use high PUFA dietary fat sources for energy like this one. At first glance it seems like carbohydrate restriction resulted in drops in T3 just like calorie restriction.

When you dig deeper and see that 55% of the calories came from PUFA high in LA it becomes impossible to know what caused the T3 drop. PUFA or carbohydrate restriction. Additional long-term studies on carbohydrate restriction like this 2-year trial show a small decrease in TSH and no change in T4  which would suggest improved thyroid function.

There is one thing that trumps all the lab data in the world. How you feel! If your T3 goes down during weight loss but you feel amazing don’t worry about it. T3 levels are tightly regulated by your body by the ability to turn T4 into rT3 instead of active T3 and the ability to up regulate and down regulate T3 receptor function through expression.

So, we should focus more on how you feel and less on what your numbers say. It is also apparent that carbohydrate consumption alone increases T3 levels and as dietary fat percentages drop these levels will go up. This is likely due to the metabolic requirements of processing carbohydrates. In this study comparing extremely high carbohydrate to dietary fat diets T3 did indeed go up from baseline with carbohydrate consumption and down with higher dietary fat consumption.

I believe the big picture summary is this. T3 responds to what the system perceives and needs. Severe calorie restriction and high LA PUFAs signal to the system that you need to slow down and either shunt T4 to rT3 or change receptor function. This could certainly result in symptomatic hypothyroidism.

However, carbohydrate restriction alone and especially when done with healthy dietary fat consumption will have much less effect on T3 levels and function. Lower levels could be the result of normalization of your hormones as weight is let go and optimal body alignment achieved.

Lower levels could also be evidence of a more efficient system and less demand for thyroid function with increased receptor expression. As a bonus human studies on longevity demonstrate an association of a longer life with lower levels of T3. Reduced T3 without symptoms may well be a sign of a well-functioning system that has reached optimal alignment and efficiency!

So, what if you do have symptoms? First and foremost, consult your health care team. If they are unwilling to order ALL the labs mentioned above find someone that is. They should also measure associated labs for directed treatment. As your doing this remember that your thyroid knows what’s going on around you! Before jumping on a medication for thyroid optimize your sleep, stress and toxic exposures. You can find one of my PHD advisory board webinars on sleep here.

Dr. Feinerman has a discussion of emotions on physical health here. In addition to working through these stressors also consider thyroid support supplements. You can find these in the PHD supplement guide in the client area.

Lastly, avoid foods known as goitrogens. These are toxic for your thyroid. If you are following the PHD permitted food list you already avoid most of these but in case you missed it avoid gluten, grains, dairy, nightshades (eggplant, peppers, tomatoes, white potatoes), sugar, caffeine, alcohol and for those with possible or confirmed autoimmune cause of thyroid dysfunction, eggs.

Cruciferous vegetables can and should be consumed but if you are worried about your thyroid be sure to cook or ferment these nutrition packed plant foods. If you have to consume dairy try goat products or A2 cow products.

In conclusion, there is a tremendous amount of noise and misinformation about the thyroid. The medical community has not done a good or even fair job of addressing this increasingly common concern. An accurate diagnosis and good understanding of what is happening can help keep those with thyroid concerns on track. Remember that thyroid hormone levels are NOT as important as how you feel.

If you are concerned, start with the basics, sleep, stress and food. Talk to your PHD team about your concerns and how to make sure you are optimizing your PHD program to support your thyroid. If you still have symptoms, consider working with your health care team to determine if treatment is right for you. It may well be temporary while your body adjusts to its new optimal you.

Additional resources:

  1. The Paleo Thyroid Solution: Stop Feeling Fat, Foggy, And Fatigued At The Hands Of Uninformed Doctors – Reclaim Your Health!
  2. The Thyroid Connection: Why You Feel Tired, Brain-Fogged, and Overweight — and How to Get Your Life Back

Supporting your Performance, Health, Diet, PHD

Dr. Doug

Douglas E Lucas, DO
Chief Science Officer
PHD Weight Loss and Nutrition

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