Keto wrecked my thyroid and metabolism
March 1, 2022

7 minute reading time

Keto wrecked my thyroid and metabolism. There, I said it. I didn’t want it to be true. That the sinking feeling in the pit of my stomach was just an overreaction. It couldn’t to be true. How could the process that had helped me lose so much weight to be the very thing that made me ill again? And, even worse, gain so much weight back. It was supposed to be THE THING. But, it was true. Keto wrecked my thyroid and my metabolism. 

Right now I am angry.

Angry that yet again, the men at the top of the nutrition food chain have led us astray. Again. The doctors and nutrition experts that taught me all about keto and fasting, KNOW. Know that long term ketosis lowers thyroid hormones. Because of this omission, keto wrecked my thyroid and metabolism.

woman with head on books is feeling tired from keto wrecked thyroid and metabolism

Keto works, but it has to be done right

Before I get into the nitty gritty of this, I want to clarify some things. This information that I am about to share doesn’t apply to everyone. Plenty of people will do really well staying in ketosis long term. Just as plenty of people thrive on a high carb vegan diet. That is the crux of the nutrition problem. 

Not everyone can do certain diets or at least, can do them long term. My whole business is based on an anti dogmatic approach to nutrition and I always coached that you have to find what works for you. That has not changed. As such, I am always learning and researching for my community to make sure that everyone has the chance to be in their best health, no matter what food or eating style suits them best.

Keto is spectacularly effective at reversing metabolic disorders and fixing blood glucose issues BUT it has to be done in a very controlled way. Keto done in short burst with regular cycling into sugar burning it key to long term thyroid and metabolic health. Too much is not a good thing. Staying for too long on keto wrecked my thyroid and metabolism.

They talk about keto and thyroid

The top dudes in the ketosphere have hypotheses about why keto can harm thyroid and metabolism. Why people on keto have lower T3 levels. I will explain what that means. They “think” it MIGHT be because we are more sensitive. But, they don’t know why exactly. They are not able to tell us why. Those of us on the ground, are suffering with a wave of symptoms. We know we have the symptoms and they know why we have them.

They know that long term keto wreaks havoc on thyroid hormones and eventually metabolism.

Ok, now I will get into the science of it. So you can see what I learned, I have posted the link to every research paper or article that I use in this post. Because there are a lot of them, I’ve put them at the bottom, so you can go and check it out yourself. I will try to make this as simple as I can but there are some biochemistry basics you need to know, to understand why long term keto wrecked my thyroid and metabolism.

woman standing on weighing scales seeing weight gain from keto wrecked thyroid and metabolism

But first, what happened to me.

First I want to give you some background on me and my journey and how I came across what is an alarming amount of evidence that long term ketosis is not a good idea for some people, especially for women, especially for women with pre excessive thyroid issues or a susceptibility to thyroid issues.

I discovered keto back in 2016 when I was at my heaviest weight ever. I topped the scale at 121kg or 261lbs. After researching a lot, trying to find the best weight loss plan, I found keto. I was already medicated for hypothyroid but I had ZERO symptoms and my weight dropped quickly and easily.

Fast forward a year and a half and I was at my lowest weight at 71kg. But something was starting to happen. I felt constantly cold, no matter what the temperature was outside. Even in the summer! My hair was starting to fall out and my skin was dry. I didn’t feel good. When I noticed my weight starting to creep up I cut right back on carbs. But it didn’t work. My weight kept climbing.

Eventually I had put 10kg back on, about 25lbs. I tried everything to get the weight back off. Super low carb, carnivore, PE diet, my own Protein Priority Diet program and fasting. Nothing was working. I couldn’t believe I was back where I started before keto – not weight wise, thank goodness. But not being able to lose weight. I was in danger of regaining everything.

I knew that something else was going on. With each new eating plan, I was losing 2 to 4kg but stopping there and it would go back on over a couple of weeks. By this point, I was despairing. Why wasn’t I losing weight?

Physician, heal thyself

Ok I am not a physician, but I am an excellent holistic nutritionist. I pride myself on being able to spot red flags with private clients and connect the dots. The dots will lead to a root cause. I needed to coach myself.

When I sat down to write a list of symptoms, I had more than TEN:

  • My body temperature was impossible to maintain 
  • I was freezing cold getting into bed each night
  • I had no energy to exercise
  • When I exercised I got fatigued really quickly 
  • Despite eating strict keto/ carnivore and calorie counting I was gaining weight
  • Inward trembling at night
  • Bad sleep quality
  • Skin so dry it would crack and bleed
  • Incredibly sensitive to cold – I didn’t want to go outside and it took me much longer to heat up when I did go
  • Brain fog
  • Nails that were splitting and peeling constantly 
  • Heavy periods 

All red flags for thyroid problems

It was screaming at me from the page. Your thyroid isn’t happy, Christina! Now that I could see the signs, I knew that I had to get tested. My TSH (thyroid stimulating hormone) came back at 2.2. This number is within the clinical guidelines. My doctor was happy and sent me on my way.

But luckily, I knew different. I do best when my TSH is between 1 and 1.25. I also have the benefit of my nutrition qualification and the vast experience working one to one with women who have thyroid problems.

As part of my nutrition education, I got a list of recommended reading. One of the books on the list caught my eye, as a thyroid sufferer. It is called “Why do I still have thyroid symptoms? When my lab tests are normal” by Datis Kharrazian. I had studied the book in detail and knew that my lab results didn’t confirm anything.

Looking for answers

So using my knowledge of research I began searching for studies that might explain. The main key components were the weight gain, thyroid and keto because they are my symptom, my issue and my way of eating. What I uncovered shocked me to my core. Study after study that pointed to keto negatively impacting thyroid. Keto had wrecked my thyroid and metabolism.

The science bit

This bit is going to explain the mechanism of the problem. It involves a bit of biochemistry but I have tried to make it as straight forward as possible.

Your thyroid is like the accelerator in a car, but for your metabolism. Hormones tell it to speed up or slow down.

If you are hyperthyroid, it’s running too fast. That means you have a fast metabolism and you find it hard to put weight on.

If you are hyperthyroid, it’s running too slow. That means you have a slow metabolism and you find it hard to lose weight.

How your thyroid hormones work

Your brain sends the hormone TRH (Thyroid Releasing Hormone) to your pituitary gland. Then your pituaitary gland takes over and releases TSH (Thyroid Stimulating Hormone). TSH stimulates TPO (Thyroid Peroxidase) to use iodine to create mostly T4 hormone and some T3. T4 is inactive so your liver needs to convert it to T3, the active thyroid hormone.

How keto stops the conversion of T4 to T3

Keto might not stop the conversion completely, but it sure does slow it down. It slows it enough that you get symptoms of hypothyroid. So how does keto interfere in this process and, more importantly, how can you make sure that keto doesn’t damage your thyroid.

Your hormones are in a delicate dance. Some hormones are not compatible. For example cortisol and melatonin. Cortisol is a stress hormone and melatonin is the hormone for sleep. If your cortisol is high, you won’t produce much melatonin and your sleep can be bad quality or you might even suffer from insomnia.

Cortisol, the culprit

Cortisol also blocks the conversion of T4, the inactive hormone, into T3 the active hormone. Because cortisol is a stress hormone, your body prioritises it. After all, its job is to keep you alive. It’s one of the fight, fight, flee hormones. It’s a vital hormone.

High chronic stress levels keep your cortisol levels high. This is why when you’re super stressed, you can find it hard to sleep. Or if you do sleep, it’s not great and you feel tired even after a whole night.

What else keeps cortisol high? Keto and Fasting.

Keto and Fasting keep cortisol high

Very Low Carb (Keto level) = High Cortisol

Ketosis is when your body doesn’t have enough sugar to fuel it. So your liver starts to make ketones for fuel. That is the simple version, obviously it’s a lot more complicated than that. When your body signals your liver to make ketones (called ketogenesis), it pumps out cortisol, which is one of your stress hormones. 


Cortisol stays higher the longer you go without carbs. Carbs give your body glucose that it uses for fuel, reducing or switching off making ketones. It’s a self regulating system that you control by how you eat. How many carbs you eat. If you don’t eat enough to fuel your body’s systems, ketones will be made. And here is the root of the problem.

Cortisol stops the conversion of T4 to T3

Very High Carb (300g+) = High Cortisol

The same goes for very high carb diets. When your blood sugar spikes, insulin comes out to take the sugar out of your bloodstream and either sends it to your cells for fuel, sends it to be stored and then converts what is left to fat.

But if you have high spikes, insulin will bring your blood sugar down and if it goes below a certain level you experience a blood sugar crash. When that happens your body needs to act quickly so that you don’t pass out. It pumps out cortisol so that glucagon (the hormone that raises blood sugar) raises your blood sugar.

Zero Carb/Carnivore/Fasting = High Cortisol

When you are zero carb you are constantly making ketones and glucose (called gluconeogenesis) because there are cells in your body that only use glucose for fuel. So you need some sugar in your system. If you are fasting a lot, on a carnivore diet that doesn’t include honey or fruit, or are doing zero carb in another way, your body needs to keep cortisol high to keep that vital sugar in circulation.

When I think about what fasted exercise does to cortisol.. EEK. If you are a woman and you exercise whilst fasted, stop now. Eat before you work out. Eat easily digested, whole food carbs. 30g to 40g is more than enough. Protect your thyroid!

What to do now?

Start by watching the video. I know it’s long but it’s probably going to answer all of your questions.

Recovering my keto wrecked thyroid and metabolism.. and yours too

I am working on a million things right now to address this problem. Keto is a powerful and valuable tool for health and recovery if it’s done right. The first step is to understand what “right” means because chances are, it’s going to be different for everyone. That makes coming up with a plan, hard. But I am stepping up to the challenge.

The second step is a recovery plan. A metabolic recovery plan and a thyroid recovery plan. Both need to be separate because if you have thyroid issues, your metabolism isn’t going anywhere. But if your thyroid is slow because of cortisol, it’s easier to recover.

I don’t have the answer, YET. But I sure am working on it. If you want to work with me one to one for private nutrition coaching, send me an email or DM me on any social media platform.

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