Low thyroid tends to affect the mitochondria negatively, when you then eat a keto diet, all the energy from ketogenesis goes directly to the mitochondria (which are often malfunctioning), to produce energy.

This will worsen energy levels and weight for the majority.

You are taking the fatty acids of fat and transporting that into the mitochondria, and if there are any issues with the carnitine-shuttle, then there are going to be problems. On top of that, then you are doing a fatty acid oxidation, so you are breaking that down into acetyl-CoA and making it go through Krebs cycle and the electron-transport chain.

This results in a very poor energy outcome in cases where there is mitochondrial malfunction.

Typically, when our thyroid is not working, we are struggling with chemical, infectional and/or heavy metal load, which is affecting the mitochondrial function.

We do not want our energy production to have to go through this malfunctioning pathway then - we want to focus on glycolysis instead.

We want easy-to-access-energy through complex carbs, when our thyroid is low, because our mitochondria is not working properly to produce energy from the ketones.

Now Ideally keto is supposed to be good to optimize mitochondrial function.

This, however, really depends on the reasons for low mitochondrial functioning and how all the other markers look, as they relate to thyroid, liver and toxic load.

Humans are not just one single number.

Too often we focus solely on blood-sugar, yet all the markers need to be taken into account, when we want to understand, whether a diet strategy is good for us or not.

Keto mainly works well for people who have well-functioning mitochondria and no thyroid issues - and this is why it is critical that we ask ourselves:

is what I am eating making me feel better?
Is it easy for me to keep my weight stable?
Do I sleep well?
Is my blood-sugar on point?
How is my CRP, triglycerides, homocysteine, and LDL?
How are my cortisol levels signs of adrenal fatigue?
How are my hormones?
Am I always tired?

If any of these questions are off, chances are, whatever diet you are following - keto, carnivore, vegan, intermittent fasting or otherwise - may not be a good match for you right now. But again, right now doesn’t mean forever.