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Insulin Resistance and Thyroid Health

Published March 4 2013

Insulin resistance occurs when the body becomes resistant to the effects of insulin. This is almost always caused by diet, and if unaddressed can eventually lead to type II diabetes. Many people with thyroid and autoimmune thyroid conditions have insulin resistance, and the good news is that this condition can be reversed. In fact, many times type II diabetes can also be reversed through natural methods.

Before talking more about insulin resistance, it’s probably a good idea to briefly discuss the role of insulin. Insulin is produced in the pancreas, specifically within the beta cells of the islets of Langerhans. Many people know that insulin is given to many diabetics to help lower their blood sugar levels. So without question, insulin plays a very important role in helping to balance the blood sugar levels. But in addition to this, it also has other functions. For example, insulin plays a role in DNA replication and protein synthesis. It also plays a role in lipid synthesis, along with the uptake of amino acids.

Insulin also is important for the health of the liver. And many of you know that a great deal of the conversion of T4 to T3 takes place in the liver. As a result, if someone has insulin resistance, then this can potentially cause problems with the conversion of T4 to T3.

Signs and Symptoms of Insulin Resistance

Some of the signs and symptoms associated with insulin resistance include sugar cravings, fatigue, and weight gain.  Of course many people with thyroid and autoimmune thyroid conditions have these symptoms, and they’re not always related to insulin resistance.  So it can take some detective work to determine if someone has this problem.

How does insulin resistance develop?  As briefly mentioned earlier,  eating a poor diet is the main cause.  Although there are a lot of health conscious people who read my articles and blog posts, people in general are eating too many refined foods and sugars.  And many of those who are trying to eat healthy are still consuming too many carbohydrates on a daily basis.  For example, we all know that cookies, cakes, potato chips, candy, and many other foods are not good for us.  Eating these foods on a regular basis is a big factor in the rise of insulin resistance and type II diabetes.

However, some people who avoid these foods still have problems with insulin resistance.  I’ve consulted with people who are gluten free, yet are eating well over 300 grams of carbohydrates per day in the form of gluten-free grains (quinoa, millet, brown rice etc.), potatoes, gluten-free pastas and bread, etc.  So just because someone is avoiding pastries, potato chips, candy, pizza, and other junk food doesn’t mean they are doing fine with their daily intake of carbohydrates.

Testing For Insulin Resistance

One way to help determine if someone has insulin resistance is by the fasting blood glucose test.  This isn’t a specific test for insulin resistance, but if someone has a glucose level of 100 mg/dl or greater, but less than 125 mg/dl, then one can pretty much conclude that they have insulin resistance.  The Glucose tolerance test is another test which can help determine if someone has insulin resistance.  With this test the person fasts for a minimum of eight hours, and then they drink a sweet solution, and two hours later their blood glucose levels are measured.  If the levels are between 140 and 199 mg/dl then insulin resistance is a factor.  It’s also a good idea to test the insulin levels, which should be less than 5 when fasting, and less than 30 after drinking the solution.

There are some other tests you can look at to help determine if someone has insulin resistance, but these are the main ones.  Something else to look at is the total cholesterol and triglycerides, as if the triglycerides are higher than the total cholesterol then this also means that the person has insulin resistance.  However, just because someone’s triglycerides are lower than their total cholesterol doesn’t mean they don’t have insulin resistance.

The Impact On Thyroid Health

As I mentioned before, insulin resistance can potentially affect the conversion of T4 to T3 in the liver.  However, it can affect the thyroid gland in other ways as well.  Thyroid hormone plays a role in glucose metabolism, and numerous studies reveal how insulin resistance affects thyroid health.  One study showed that insulin resistance can increase thyroid proliferation (1).  Another study showed that both hyperthyroidism and hypothyroidism can affect the blood sugar levels and lead to insulin resistance (2, 3).   Yet another study showed that people with insulin resistance have a higher prevalence of thyroid nodules and bigger thyroid glands (4).

Insulin Resistance, Inflammation, and Weight Gain

The increased glucose associated with insulin resistance can cause a lot of problems.  First of all, increased glucose can activate NF-kappaB, which can lead to inflammation.  Second, insulin resistance also will activate adipocytes, making it difficult for people to lose weight.  Finally, insulin resistance will upregulate the enzyme aromatase (5), which can lead to estrogen dominance.  While eating well is important to correct this condition, doing this might not correct the inflammatory process and/or estrogen dominance condition.

How To Correct Insulin Resistance

When it comes to correcting insulin resistance, a lot of this really does come down to improving one’s diet.  Exercise is also a factor, as it is important to exercise regularly.  However, as I mentioned before, if NF-kappaB is activated and/or if someone has estrogen dominance due to insulin resistance, then these need to be addressed.  So in order to correct insulin resistance one needs to do the following:

So hopefully you have a better understanding of what insulin resistance is, how you can determine if you have this condition, and what you can do to correct it.  The good news is that in most cases, modifying one’s diet can greatly help with insulin resistance.  Of course for many people who are accustomed to eating refined foods frequently this can be a challenge.  But just as is the case with many other health conditions, those who are willing to take responsibility for their health and make the necessary sacrifices will reap the benefits.  On the other hand, those who aren’t willing to do this will most likely develop other health issues in the future, with type II diabetes at the head of the list.


1. Rezzonico J, Rezzonico M, Pusiol E, Pitoia F, Niepomniszcze H.Introducing the thyroid gland as another victim of the insulin resistance syndrome: Thyroid. 2008 Apr;18(4):461-4. doi: 10.1089/thy.2007.0223
2. Kapadia KB, Bhatt PA, Shah JS.; Association between altered thyroid state and insulin resistance; J Pharmacol Pharmacother. 2012 Apr;3(2):156-60. doi: 10.4103/0976-500X.95517
3. Brenta G.; Why can insulin resistance be a natural consequence of thyroid dysfunction?; J Thyroid Res. 2011;2011:152850. doi: 10.4061/2011/152850. Epub 2011 Sep 19
4. Rezzónico J, Rezzónico M, Pusiol E, Pitoia F, Niepomniszcze H; Metformin treatment for small benign thyroid nodules in patients with insulin resistance; Metab Syndr Relat Disord. 2011 Feb;9(1):69-75. doi: 10.1089/met.2010.0026. Epub 2010 Dec 3
5. Williams G.; Aromatase up-regulation, insulin and raised intracellular oestrogens in men, induce adiposity, metabolic syndrome and prostate disease, via aberrant ER-α and GPER signalling; Mol Cell Endocrinol. 2012 Apr 4;351(2):269-78. doi: 10.1016/j.mce.2011.12.017. Epub 2012 Jan 5