Ketosis and Hypothyroidism

I see questions like this all the time, so let’s address a question I received this week. A women commented:

“I seem to be struggling with weight loss, and when my doctor tested my thyroid he told me that I have low thyroid function. I never had ‘low thyroid function’ before changing my diet. Did eating ketogenic cause this problem?”

The simple answer is maybe. This is a complicated issue to sort out and I do not want to scare anyone off, so let’s dive into the details. In previous posts (“Keto Problems: Too Little Carbs?” and “Troubleshooting Guide Part II“), I mention that thyroid problems are a common complaint amongst those eating a low carb diet. Many people have low or declining thyroid function before beginning a low carb diet. However, as noted in the question above, some people do develop thyroid disorders only after eating a low carb diet. While it may seem obvious that eating low carb caused the thyroid to slow, all the possible causes need careful consideration. This does not happen to every low carber and there are good reasons why.

What is the thyroid? Why does having “low thyroid function” matter?

The thyroid is the metabolic powerhouse of the body. It governs the metabolism, which is how efficiently we burn fuel, and also regulates growth, maturation and body temperature (Mullur, Liu and Brent, 2014). The thyroid gland produces hormones T1, T2, T3, T4. The hormones that regulate metabolism are triiodothyronine (T3) and its precursor hormone, thyroxine (T4). The pituitary gland produces thyroid stimulating hormone (TSH) and signals the thyroid to produce inactive hormone, T4, which is then converted to active hormone, T3. The more efficiently the body converts T4 to T3, the faster the metabolism. A faster metabolism burns body fat efficiently and is less likely to see weight gain, so this is why having a “fast” or “slow” thyroid is a big deal to people hoping to shed body fat. However, there is a goldilocks effects, which means that there is a such thing as a metabolism being “just right.” If the body either produces or converts too much hormone, then the person is considered to have fast thyroid function and be hyperthyroid. If this action happens too slowly, then the person is considered to have low thyroid function and be hypothyroid. However, hypothyroidism, or a slow metabolism, is a common complaint among those who eat low carb diets for more reasons than just slow weight loss.

Signs of hypothyroidism

If you experience any of the symptoms below, you may want to have your thyroid levels checked to determine whether you are developing clinical hypothyroidism:

  • Slow, insidious weight gain
  • Inability to shed body fat no matter what you do
  • Hair loss
  • Fatigue
  • Constipation or slow motility (you should be going to the bathroom daily)
  • Insomnia or difficulty staying asleep
  • Dry skin
  • Cold hands and/or cold feet
  • Wanting to nap every day
  • Dry, brittle hair and nails
  • Loss of curls in previously curly hair
  • Weak arms
  • Slow reflexes
  • Brain fog, difficulty concentrating, memory loss, confusion, forgetting words
  • Low body temperature (under 97.8° in the AM and under 98.6° mid afternoon)

A good doctor will diagnose and treat you based upon both test results and symptoms, so pay close attention to how you feel. If you never experienced any these symptoms before eating low carb, however, and then develop them suddenly while eating low carb, there may be several reasons why this is occurring.

Why is hypothyroidism common in ketosis?

It is common because people often fall into one of the categories below, whether they know it or not.

  1. You may not be eating enough calories. Many people have a long relationship with dieting. We have been taught the calories in/calories out method for weight loss, and we believe that cutting calories is the only way to mobilize body fat. However, Wadden and colleagues (1990) showed that lowering calories in obese subjects (who have body fat available to burn) resulted in a significant decrease in the body’s T3 production. Instead of creating T3, the body created reverse T3, which is considered a metabolic dead end that can occur when the body is in starvation mode, fasts too frequently and/or does not get enough food. When subjects were subsequently fed more calories, their T3 production increased. Because eating a low carb diet can change how the body metabolizes food (perhaps in ways that are not even understood by scientists), it is critical to eat a lot of fat to replace carbohydrates as the primary fuel source. The body is able to convert fat to glucose while in ketosis, but there must be enough fat available for this conversion to occur. Body fat is not the same as dietary fat, as cutting calories low can signal the body that there is not enough new fuel coming into the body. Undereating is often a trigger for down-regulating and slowing the metabolism to preserve life function, despite having excess fat stores on your frame. You must eat enough to access body fat without slowing your metabolism (click HERE for details on how to determine your macros and caloric intake). The lesson here? If you have hypothyroidism, you may need to eat more calories.
  2. You may not be eating enough carbs. This is a weird one to explain to people who follow a low carb diet, but low carb does not actually have to mean “no carb.” There are people who are successfully eating a zero carb diet of meat, eggs and dairy only, but there are no scientific studies that examine how well their endocrinological or metabolic systems function. However, many zero carbers eat very high amounts of animal proteins, which makes all the difference. Low carbers, on the other hand, are more likely to calorie restrict while they carb restrict. Danforth and colleagues (1979) fed subjects low carb and high carb diets to maintain their weight (approx. 2,000 calories) and also overfed subjects (approx. 4,000 calories) using both low carb and high carb diets. Their study found that those who ate enough to maintain their weight with lower carb levels saw significant decline in thyroid function, but those who ate both high carb diets and excess calorie diets had higher T3 levels. The lesson here? If you find that increasing calories is not enough, then increasing carbohydrates is the next step. Remember that you can be in fat burning mode without having excess measurable ketones simply by eating under the body’s daily need of 120+grams of glucose. If you prefer to see measurable ketones, then you will likely have to eat fewer but limiting to 15-20 grams per day is not at all necessary. Read this article for details on eating the right amount of carbs for your body.
  3. You may have autoimmune thyroid condition called Hasthimoto’s Thyroiditis, Euthyroid Sick Syndrome, Wilson’s Temperature Syndrome, a gut infection or some other sickness. I will not go into details, but I will say that if you are eating enough calories and enough carbohydrates and are still showing symptoms of hypothyroidism, then your doctor and you need to do some further investigating to address the root cause of your condition. Work with a good functional medicine practitioner if you can, as traditional medical doctors are likely to dismiss the conditions above as insignificant until you become very sick.

Is there any good news?

Yes! The good news is that hypothyroidism is treatable and can be reversed with proper diet, nutrition and supplements for those who need them. The most important thing that you can do to maintain your health on a low carb diet is to take good care of your body. Rather than starving yourself skinny and making yourself sick, be sure to feed your body healthy, nourishing foods in adequate quantities to sustain your lifestyle. If you eat right and eat enough, then a low carb diet should absolutely enable you to reach the pinnacle of health and vitality.


Danforth E, Jr, Horton ES, O’Connell M, Sims EA, Burger AG, Ingbar SH, et al. (1979) Dietary-induced alterations in thyroid hormone metabolism during overnutrition. J Clin Invest. 64:1336–47.

Mullur, R., Liu, Y.-Y., & Brent, G. A. (2014). Thyroid Hormone Regulation of Metabolism. Physiological Reviews, 94(2), 355–382.

Wadden TA, Mason G, Foster GD, Stunkard AJ, Prange AJ (1990) Effects of a very low calorie diet on weight, thyroid hormones and mood. Int J Obes 14: 249–258. is a news aggregation service that brings you best of world articles to you for your consumption.

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