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Q & A: Thyroid and Low-Carb Diets

I have heard that the body needs carbohydrates to make thyroid hormones.  Does a low carb diet affect thyroid hormones?

Studies find that lower carbohydrate diets can indeed lower T3 levels.  Conversely higher carbohydrate intakes can lead to higher T3 levels.  But before you get too excited, it’s important to know that any lower calorie diet can lower T3 hormone. So can intense exercise.  Yes that’s right - during and for a time after intense exercise, it is common for T3 levels to be lower. 

The body responds to calorie deficits from diet or exercise by lowering T3, because it protects against the breakdown of muscle. 

So if diet and exercise can both lower T3, how do people ever lose weight?  They lose weight when they successfully shift enough pathways to increase fatty acid oxidation in the body.  While T3 may drop somewhat with diet and exercise, this says nothing about a person’s overall regulation of body weight based on these and other hormone fluctuations. 

If low carb diets cause drastic reductions in T3, why do we see so many studies showing people losing weight on low carb diets? Head to head studies of high versus low carbohydrate diets consistently find that the lower carbohydrate diets lead to more weight loss as loss of fat not muscle, in addition to leading to greater improvements in blood sugar levels and improved lipid profiles[1]

In fact, some studies suggest that there may a metabolic advantage to low carb diets[2]. Not only that studies have found that lower carbohydrate diets protect a person’s resting energy expenditure (REE, a person’s rate of caloric burn at rest) MORE than lower protein high carbohydrate diets, possibly because the increased protein helps preserve your muscle[3]This would not be possible if thyroid hormone activity was drastically lowered.

Some people do seem to exhibit low thyroid symptoms on low carb diets. Why is that?

Over the years, I have observed a subset of people who struggle with low carb diets.  They notice an almost immediate effect on mood and energy, along with dramatic and significant cravings for carbohydrates.  When they begin eating carbohydrates again, the person often gains all the weight back they lost and sometimes more. 

Why is it that some people can be successful on a lower carbohydrate diet while others cannot?  It may be because they have different predominant underlying causes for their weight gain in the first place.

For example, it is known that insulin resistance can cause a reduced conversion of T4 to T3 hormone[4], which is the physiologically active form of thyroid hormone.  When insulin resistance is addressed, with whatever combination of measures diet, exercise, added magnesium, chromium or alpha lipoic acid, for example, the cells can once again start using glucose for energy and T3 production picks up.  So for a person who is insulin resistant, a lower carbohydrate diet may be all that is needed to help restore better T4 to T3 conversion and weight loss will be achieved.

For other people, another factor such as long-term chronic stress may be affecting their response to low carb diets.  We know that chronic stress can interfere with thyroid hormones in several ways.  First it can shift tyrosine, needed for T4 production, to cortisol production.  Secondly it can reduce serotonin, which plays a role in T4 to T3 conversion. 

When T4 to T3 is disrupted, there is often an increase in the production of something called reverse T3 (rT3).  rT3 can cause an increase in the production of substances known as thyronamines that can cause symptoms similar to low thyroid (low basal body temperature and fatigue) along with insulin resistance symptoms of increased blood sugar[5]

So this creates quite a problem for some people. While a low carb diet may help address the insulin resistance, for a person who had high chronic stress already contributing to lowered T3 conversion, the further drop in T3 from the low carb diet along with the increased rT3 can lead to low thyroid symptoms.  If we also have lowered serotonin, this causes the whole storm of lowered mood, lowered energy and carb cravings, even though in many, if not most cases, they are losing weight. 

So what should these people do?

The answer is not to eat higher levels of carbohydrate because it continues to exacerbate the insulin resistance.  If the person chooses a higher carbohydrate low calorie diet, T3 can still drop due to the lowered calorie intake.

I have seen some practitioners suggest that because the metabolic pathways have to make such a significant shift in these cases, the best thing to do is to  lower carbohydrate intake but lower it gradually, not all at once.  

In my experience, people will get a quicker and more satisfying answer to these problems by using dietary supplements that help manage the body’s stress response, which can help reduce cortisol, freeing up tyrosine for thyroid and help build serotonin levels, which can reduce the carb cravings and help improve T4 to T3 conversion. 

I typically use the combination of supplements I’ve discussed before, like Rhodiola (reduces stress hormone cortisol), Holy Basil (reduces stress response and can support healthier blood sugar levels), Relora (reduces stress response and helps reduce carb cravings) and/or L-theanine (helps people feel calmer and is particularly good when people are feeling anxious) and 5 HTP (needed for serotonin, so can help with feeling calmer, reduced cravings and better sleep.)

This question brings up and, once again, supports the fact that in order to be successful with weight loss you have to evaluate and address underlying metabolic issues.

Interestingly many of the issues that can affect success in weight loss do so by their influence on the conversion of T4 to T3 thyroid hormone.

This is because there are numerous factors that influence the enzymes responsible for this conversion, called deiodinase enzymes.  People need to be aware of these, so they can be systematically addressed.

Other Factors that Can Depress Thyroid Hormone Activity

1.  Inflammation – inflammatory cytokines are known to depress T3 levels[6].  This is where the quality of the diet is so important.  People who do low carb but who do not eat tons of non-starchy vegetables and a little fruit to get those antioxidants in are not going to be as successful with their weight loss.  Spices like ginger, turmeric and rosemary are also potent antioxidants. Those fruits, vegetables and spices actually help restore the enzymes that can convert your T4 to the active T3 form.

2. Trace Minerals – the body needs several minerals and trace minerals to keep thyroid hormones being produced.  Iodine is needed to make T4.  Selenium, iron, chromium and zinc are needed as co-factors to activate the deiodinase enzymes that remove that one iodine molecule to make T3, the active form of thyroid hormone.

3. Sex Hormones – testosterone is important in men to help maintain insulin sensitivity with helping thyroid conversion enzymes[7].  In women estrogen dominance can promote fat storage[8]. Anyone who is having trouble losing weight and who has explored and supported other areas should remember their hormones could also be playing a role.    Remember too that stress hormones can interfere with sex hormone production, so it is often necessary to address stress hormone chemistry in conjunction with other hormones.

4. Environmental Toxins – there are many chemicals in the environment that interfere with thyroid hormones by either blocking the receptors in cells or by interfering with conversion of T4 to T3[9].  Mercury, bisphenol A, PCB’s and styrene are some of the known potent thyroid hormone disruptors. So take measures like avoiding BPA-containing plastic containers and can linings and styrofoam food containers, cups and plates.  Also, control your intake of high mercury fish, like tuna.  In addition, take measures to help your body’s detoxification processes.

5.  Gut Health - And finally the health of the gut can have huge affects on all these areas.  If the intestinal cells are breaking down due to overgrowth of yeast and inadequate beneficial flora, the absorption of the trace minerals so essential to thyroid hormones can be dramatically reduced.  In addition, food sensitivities, which can develop due to imbalances in flora, can cause increased cortisol, can be a source of inflammation, and can also go on to cause an autoimmune attack on thyroid hormones, called Hashimoto’s Thyroiditis.  Hashimoto’s is the most common cause of hypothyroidism.

Thanks for this great question.  There is a great deal of discussion around this matter all over the internet, and unfortunately most people use the confusing mix of information from studies simply to support their view.  The interplay of thyroid hormones diet, exercise, and other factors is complicated, but I have had great success with low carb diets, especially when we support other metabolic needs in the body.

Written By Jim LaValle, R.PH, CCN

This article is not intended for the treatment or prevention of disease, nor as a substitute for medical treatment, nor as an alternative to medical advice. Use of recommendations in this and other articles is at the choice and risk of the reader.

[1] Shai I, et al. Weight loss with a low carbohydrate, Mediterranean or low fat diet. NEJM July 17 2008;359: 229-241.

[2] Westman E, et al. Low carbohydrate nutrition and metabolism. Am J Clin Nutr August 2007 vol. 86 no. 2 276-284

[3] Mojtahedi MC, et al. The effects of high protein intake during energy restriction on changes in body composition and physical function in older women. J  Gerentol a J Sci Med Sci doi:10.1093/gerona/glr120

[4] Islam S, et al. A comparative study of thyroid hormone levels in diabetic and non-diabetic patients. SE Asian J Trop Med Public Health 2008;39(5):913-916.

[5] Piehl S, et al. Thyronamines - past, present and future. Endocrine Reviews, February 2011, 32(1):64–80

[6] Nagaya T, et al. A potential role of activated NF-Kappa B in the pathogenesis of euthyroid sick syndrome. J Clin Invest 2000;106(3):393–402.

[7] Miyashita K, et al. Regulation of rat liver type 1 iodothyronine deiodinasemRNA levels by testosterone. Mol Cell Endocrinol 1995;115:161–167

[8] O’Sullivan A, et al. Efficient fat storage in premenopausal women and in early pregnancy: a role for estrogen. J. Clin. Endocrinol. Metab. 2001 86: 4951-4956.

[9] Boas M, et al. Environmental chemicals and thyroid function. Eur J Endocrin May1, 2006;154: 599-611.


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Reader Comments (1)

I would not mind trying these suppliments, but there are so many listed here. Plus already take other supplilments for other reason. Isn't there something that combines all into one?


June 24, 2012 | Unregistered CommenterKelley

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