The ketogenic diet is currently sweeping the internet and the diet book world as the best thing since sliced bread for everything under the sun. Unfortunately, you can’t eat bread on the ketogenic diet and it really can be difficult to follow for some people.

Since I work with many patients who have Hashimoto’s disease and hypothyroidism, I wanted to investigate whether the ketogenic diet can cause hypothyroidism or decrease thyroid function. Let’s jump into the research and see what it has to say.

First let’s look at a study done on epileptic kids who followed a ketogenic diet since epilepsy was the first condition to be thoroughly studied and treated with a ketogenic diet. The first thing the authors point out is that we already know calorie restriction lowers T4 and T3 levels. The ketogenic diet mimics fasting so it makes sense that it could lower these thyroid hormone levels. They point out that the ketogenic diet is anti-inflammatory, anti-oxidative, and it balances neurotransmitters.

The authors state that the ketogenic has been documented to be helpful for the following conditions:

Polycystic ovarian syndrome (PCOS)

Migraine headaches

Autism

Depression

Diabetes mellitus type 2

Amyotrophic lateral sclerosis (ALS)

Alzheimer’s disease

Parkinson’s disease

Obesity

Glucose transporter protein-1 (GLUT-1) deficiency

Pyruvate dehydrogenase deficiency

In this study, 120 patients (63 male and 57 female) aged 4-10 were treated with a ketogenic diet for one year and their TSH, Free T4, and Free T3 levels were checked at 1, 3, 6, and 12 months. 20 patients (16.7%) in total developed hypothyroidism within the first 6 months which required thyroid medication. 70% of the 20 patients who developed hypothyroidism were girls as expected. Hypothyroidism was defined as a TSH level greater than 5.0 uIU/L with normal Free T4 levels.

TSH levels actually increased in everyone during the first month but dropped overall at 12 months follow-up. Free T3 levels however dropped significantly overall at 1, 3, 6, and 12 months.

The interesting thing is that the authors state that none of the kids who were diagnosed with hypothyroidism based on the TSH test developed any hypothyroid signs or symptoms. It’s also interesting to note that any kid who had been taking fish oil 6 months prior was excluded from the study since we know that fish oil improves thyroid function.

The authors point out the limitations of this study including lack of total T4 and total T3 levels as well as no testing for Hashimoto’s thyroiditis antibodies such as anti-thyroid peroxidase (TPO) and anti-thyroglobulin (TG) levels. Additionally, some of the kids were on anti-epiletic drugs which are known to disrupt thyroid function.

I don’t see how this study found anything conclusive if none of the kids developed any symptoms and hypothyroidism was based on a TSH >5.0 in growing children.

We already know that low-carbohydrate diets can work very well for fat loss such is the Volek study which had patients eat 8% carbs, 61% fat (calories from fat were 25% saturated fat, 25% monounsaturated fat, and 11% polyunsaturated fat), and 30% protein. Volek measured T4 levels which remained normal but didn’t look at T3 levels however but the subjects did extremely well with their weight loss. If thyroid function had decreased then it would have been difficult to lose weight.

We know that cutting calories and losing weight will decrease T3 levels. Not only that, we know that fasting increases reverse T3 which knocks out T3 receptors. The ketogenic diet suppresses appetite quite effectively so many people just aren’t eating enough calories on the diet which will affect th...