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Will The Keto Diet Suppress My Thyroid?


Let’s get better acquainted with the thyroid and how it works; an endocrine gland that sits just above your Adam’s apple in your neck. If it gets enlarged, you can feel it and that’s what we refer to as a goiter; this can be caused by low-functioning thyroid tissue that gets larger in an attempt to keep up with the work load.

The thyroid gland is pretty much the gas pedal for your metabolism, producing Triiodothyronine (T3) and Thyroxine (T4) hormones that go to all of the cells in your body to regulate the metabolism speed of each cell. The functioning health of the thyroid can be assessed by looking at the levels of T3, T4 and TSH (Thyroid Stimulating Hormone which is produced by the pituitary gland and controls the speed of thyroid function).

Here are some of the issues that can occur with a low-functioning thyroid:

Hypothyroidism defines the state of an under-active thyroid gland. This is usually identified by a TSH level that is greater than 4.5 mg/dL, with symptoms including; fatigue, dry skin, hair loss, excessive sleepiness, swelling and weight gain.

Hyperthyroidism defines the state of an over-active thyroid gland. This is usually identified by a TSH level lower than 0.2 mg/dL, with symptoms including; fatigue, insomnia, heart palpitations, and feelings of anxiety or impending doom.

Thyroiditis is one of the common causes of an abnormal-functioning (either high or low) thyroid gland. This is usually due to an inflammatory autoimmune disease that for a period of time, stimulates a temporary overproduction of the thyroid hormone. The inflammation causes abnormal elevation in thyroid function and this may stimulate a period of hyperthyroidism.

However, after a few months the thyroid antibodies fade out, the thyroid often becomes under-functioning and hypothyroidism sets in. Testing the thyroid reveals elevated TSH levels and low levels of T3, T4 and so on.

Ok, that’s a lot of thyroid to take in, stay with me while we explore these particular hormones in relation to the ketogenic diet.


I’ll provide you with a little background of why some nay-sayers decry nutritional ketosis believing that this dietary approach suppresses thyroid function. A single study was carried out in which the T4 level dropped in the first few weeks after subjects entered ketosis. However, T4 fluctuates with a number of binding proteins, and using T4 as a screening test alone for assessment of thyroid function just doesn’t cut it, a drop in T4 alone doesn’t mean the diet is suppressing the thyroid.

In the case of nutritional ketogenic state, because of a change in the way the nucleus of the cell is handling fuel, Dr. Nally, an obesity medicine specialist and one of the leading voices in the keto community, states a number of reasons as to why a temporary lowering of T4 is commonly seen in his patients:

Excessive leptin production (which occurs in those with leptin resistance) signals increased T4 production. A ketogenic diet allows leptin signalling (and leptin resistance) to improve, and there will be a drop in needed T4.
T3 signals genetic differentiation (formation signalling) of white and brown fat. Increased conversion of T4 to T3 as the body shifts its regulation of white and brown fat causes a transient drop in T4. Again, this is normal change.

Differentiation between primary, secondary and central hypothyroidism can be completed only by looking at TSH and T4 values together. Without using both, pituitary mass or other pituitary damage could be missed.

Decreasing carb intake dramatically, moderating protein and increasing fats increases tissue sensitivity to T3, and due to this, serum T3 levels go down all the while the psychological response to T3 remains normal. In this scenario, both the thyroid and the liver have far less work to do in order to maintain a normal thyroid physiological response – which is what we want!

Dr. Stephen Phinney, a Professor of Medicine Emeritus at the University of California-Davis and one of the leading voices of the low-carb movement talks at length about the affects that a diet high in carbohydrates has on the body by forcing the thyroid or liver to greater levels of thyroid hormone production. Forcing the pancreas to produce more insulin by eating more carbs clearly doesn’t do any good for type 2 diabetics, and Dr. Phinney believes that the same logic applies here for thyroid function.

Dr. Nally goes on to talk about the affects obesity has on thyroid dysfunction whereby excessive leptin is produced by the fat cells as obesity worsens. As the fat cells “overfill”, they produce leptin. Some describe the fat cells as being in a “sick state” which leads to another level of hypothalamic-pituitary axis imbalance. The higher leptin stimulates the conversion of T4 to T3, leptin resistance can also have the effect of increasing TSH levels, which places people in subclinical states of hypothyroidism while making them feel activated by excess T3.

As a person follows a ketogenic lifestyle, insulin, leptin and thyroid function return to normal over a period of 3 to 6 months, T4 levels also normalise. Nutritional ketosis has a stabilising effect on the hypothalamic-pituitary-thyroid axis of Dr. Nally’s patients since 2005. Nutritional ketosis has dramatically helped to stabilise the 30 hormones involved with the diseases of civilisation: obesity, insulin resistance, thyroid dysfunctional states and diabetes.

Sophie Laura

Hi! I'm Sophie (Easy Keto Lifestyle). I'm a Certified Nutrition Coach and I help women who struggle with their weight to radically transform their health and body, by living a simple yet delicious ketogenic lifestyle.

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