Latest / Common Sense Health / The Thyroid Brain Connection: What Doctors Won't Tell You
Transcript
- Stephen Thomas BSc. Hons: Hello today I want to talk about thyroid hormones and low carb diets and iodine and reverse T3 and why your thyroid is not a simple bucket because online thyroid advice often sounds like this your T3 is low therefore your thyroid has tanked or just take loads of iodine if you don't need it you'll pee it out and both of those statements are far too simplistic. The thyroid system is not a bucket that you fill up with iodine until the numbers look nice. It's more like a very clever control system with sensors and signals and brakes, accelerators, conversion enzymes, tissue specific regulation, you know the whole lot. So in this video I want to make the technical stuff easier to understand, but I won't be dumbing it down too much. And the key message is this. A low T3 result is a data point. Hypothyroidism is a clinical syndrome with presentation. So those are not the same thing, are they? When someone goes low carb or keto or carnivore, it's quite common to see free T3 come down and immediately some people panic. They'll say, my thyroid has crashed. But has it? Not necessarily. T three is the active thyroid hormone that helps regulate metabolic activity. But one of the jobs of T3 is to support carbohydrate metabolism. Including enzymes involved in glucose handling and glycolysis, such as phosphofructose kinase one and pyruvate kinase, it also increases the density of glucose transporters, such as GLUT1, GLUT II, and GLUT 4. Now glycolysis is simply the process of breaking down glucose for energy. And this is where the T three pyruvate connection matters. When you run more carbohydrate through the system, you're Create more demand for the machinery involved in glucose metabolism. Pyruvate sits right at the end of glycolysis, acting as a sort of key junction point between glucose breakdown and further energy production. So if someone dramatically reduces carbohydrate intake, they may simply have less need for high levels of T3 driven glucose processing activity. So in plain English, if you are no longer running your body mainly on carbs, you may not need the same thyroid signal. To process the carbs. That does not automatically mean your thyroid has failed, does it? It may mean your system has just recalibrated. And this is why interpreting bloods the context of a ketogenic or carnivore way of eating is absolutely crucial. You cannot always judge a low carb person using assumptions built around high carb metabolism. So remember this thyroid hormone is built from tyrosine, which is an amino acid, plus iodine. You cannot make it out of carbohydrate. There is no biochemical pathway where glucose is a substrate for thyroxine synthesis. So you need carbs for your thyroid is not a mechanistic claim. It's an observation that carb restriction correlates with lower T three, and then that leap to causation that the biochemistry doesn't support is all that's going on there. So how do we tell the difference between adaptation and a genuine thyroid problem? And this is where symptoms and a full panel will matter. If 3T3 is lower, but TSH is normal, and 3T4 is normal, your your energy is good, your mood is good, your cognition is good, your body temperature feels fine, bowels are working, libido is fine, and you feel better than before, that looks very different from someone who is genuinely hypothyroid. But If your TSH is climbing persistently, your free T four is dropping, your reverse T three is very high, and you're cold or constipated, exhausted, foggy, puffy, losing hair and getting worse over time, that is a different picture. So the rule is simple here. Adaptation should feel fine or better. If it feels worse, don't just call it adaptation and ignore it. And this is where other factors need to be considered before simply supplementing. Often it is simply under eating or stress or lack of sleep. It could be under eating protein or overeating fat. You know, just taking iodine drops? Well that's not really joined up thinking. That's sticking a motivational quote over the engine morning light. I also believe that the hormones themselves are often misunderstood. For example, reverse T3. Reverse T3 often gets described as if it's some sort of waste product, but it isn't. Reverse T3 is not just thyroid rubbish floating around the bloodstream waiting to be blamed for someone's fatigue. Reverse T3 is made from T4, just like T3 is, it has the same atoms but it's arranged differently. That different arrangement means it does not activate the thyroid receptor in the same way that T3 does. Think of it like a Q that looks almost right but doesn't open the lock. But the important point is this. The body does not make reverse T3 for no reason. Reverse T three is part of a break in system. When the body is under stress, under eating, overtraining or inflamed, it may divert more T4 away from active T3 production and towards reverse T three. Now that's basically the body saying you're overdoing things, you need to slow down. That means the body is deliberately downshifting metabolic output. Now, the enzymes involved in this are called diidionases. there are different types that play different roles, types 1, 2, and 3. I shall call them DiO1, DiO2, and DiO3 from now on. Now, these enzymes decide what happens to the thyroid hormones in different tissues. So DiO1, mainly in the liver and the kidney, and it helps with peripheral conversion of T4 to T3. DiO2 Is found in places like the brain, the pituitary, and brown fat, and it helps activate T4 into T3 locally. DiO3 helps inactivate thyroid hormone and is involved in making reverse T3. So reverse T3 is not waste, it is part of the body's control system. The problem is not that reverse T3 exists, the problem is when the person gets stuck in a state where T3 is low and reverse T3 is high and they feel awful. And that's when you need to ask why the brake is being pressed. Now here's a massive point that gets missed all the time. The brain is a separate organ when it comes to thyroid hormone. Your brain does not simply rely on the amount of T3 floating around in the blood. The brain has its own local thyroid hormone regulation. It mainly imports T4 and then uses DiO2, one of those diodenases. one of those enzymes to convert T4 into T3 inside the brain. That T3 is made locally and used locally. And this matters because when you measure T3 on a standard blood test, you are measuring what is in the bloodstream. You are not directly measuring T3 inside the brain. You are not directly measuring T three inside the liver, muscle, gut or heart either. The bloodstream is a transport system. It is not a perfect mirror of what every tissue is doing. So when someone says your blood T3 is low, therefore your brain must be starved of thyroid hormone, that's too simplistic. The brain has its own chef in the kitchen. The thyroid sends the ingredients, mainly T4, and the brain does some of the final cooking itself. And the chef is DIO2. The blood brain barrier controls what comes in and obviously what goes out. T4 crosses in. The T3 is made inside. It doesn't come back out. It's made behind the barrier, used behind the barrier and never reaches circulation. The brain's T3 is never in the blood at all, which means no blood test can see it. Ever. So serum T3 reflects the peripheral pull. Thyroid secretion plus peripheral conversion. It excludes brain T3 entirely because the brain's T3 never enters the blood. The bloodstream, like I say, is the delivery system, not a mirror of what's happening inside tissues. But here's the part nobody talks about, and it's where most of the online debate goes wrong. They look at the tanked T3 and think it reflects the whole body and say the proof is I have brain fog. But as I've just said, the brain does not rely on blood T3. It makes its own. DIO2 is expressed in the brain in astrocytes, the support cells, and it's actively inversely regulated. So when T4 is low, DiO2 activity goes up. Why? Because the brain cannot go without T3. It's the most metabolically demanding organ in the body. So when raw material is scarce, the brain compensates by converting a higher percentage of whatever T4 it does get into active T3. Now let's move on to iodine. Iodine is essential for making thyroid hormones. No iodine, no thyroid hormone. That is true, that's simple. But the mistake people make is thinking that because iodine is essential, more must be better. And this is where things go wrong. The thyroid needs iodine, but it also has safety mechanisms for too much. And one of those mechanisms is called the Wolf Chikoff effect. When too much iodine floods the thyroid gland, the thyroid can temporarily shut down the process of attaching iodine to tyrosine. And that attachment step is called organification. In simple terms, it's like the thyroid saying, We've got too iodine, it's arriving too quickly. Shut the production line down before things get out of hand. That is not the kidney failing to excrete iodine, by the way. That is the thyroid protecting itself. And this is where the your pee it out argument misses the point. Yes, the kidney excretes iodine, but the thyroid is not the kidney. The kidney can dump iodine into the urine while the thyroid can simultaneously react to excess iodine by applying the brakes. Both things can be true at the same time because they're different organs doing different jobs. The kidney does excrete, but the thyroid regulates, so saying you'll pee it out is only half the story. It describes the plumbing but ignores the fuse box. This is where urine iodine testing becomes really useful. A proper iodine clearance test can help. assess whether someone appears to be retaining iodine or excreting it. In simple terms, if someone is deficient, the body tends to hold on to more, and if they are replete, they tend to excrete more. So yes, urinary iodine testing can be very useful. I find it particularly useful because when you have the test you're given some iodine and then your urine is measured. It's it's really that simple. And I often get messages from people doing the test from the actual lab before the results have been given saying, I am deficient in iodine, I've just taken the iodine they give me and I feel brilliantly. But how much iodine can a person take safely in one go? That's a really important distinction and the urinary iodine test can help assess the supply. And it does not mean that mega dosing is automatically safe. If someone genuinely needs iodine, the sensible approach is usually to correct it carefully and gradually, especially with the bigger picture in mind, something like potassium iodide at 200 micrograms, not milligrams. That's a good start normally. Anyway, because excess iodine may trigger issues in susceptible people, including thyroid autoimmunity. And this is also where selenium matters here too because selenium is needed for the deodinase enzymes and for antioxidant defence inside the thyroid. So iodine without considering selenium is not joined up thinking either. It's like flooring the accelerator while forgetting the brakes steering the MOT. You've got to do the whole thing. Finally, I get asked a lot, do women especially need carbs for hormones? And the honest answer is carbohydrate restriction itself is not established to lower estrogen or progesterone in any direction. It's not causal. The claim is usually built on inference, not evidence. So put simply, carbohydrates are not a substrate for sex hormone synthesis. Cholesterol is. The steroid backbone is cholesterol, which becomes progesterone, androgens, estrogens. Fat and cholesterol supply that, which explains why some people will increase their fat and see their production go up Because we are a system. I mean protein supplies the aromatase and enzyme machinery for the sex hormones, and carb supply none of it directly. The pathway that matters is energy availability and thyroid peripheral signaling. And those are where you look when something's off. And again, it can come back to under-eating or stress or lack of sleep, etc. And then people talk about insulin. Insulin is what's called a permissive signal for ovarian stuff. steroidogenesis and we have proven that stimulated insulin when it's tested protein is a very significant stimulus to insulin production in appropriate amounts. So all the inference about carbs is just a leap of faith really. Anyway, energy availability is the real driver. This is the crucial distinction. When total energy intake drops Whether from low carb or fasting or plain under eating, the hypothalamus senses this reduced energy availability and can suppress many things like GNRH pulsatility, and that's where you get hypothalamic amenorrhea. You know, it's it's an energy problem. It's not a carbohydrate problem. A well-fed carnivore eating adequate protein and fat is not. energy deficient. So this mechanism won't be firing. Everything will be fine. So let's pull this all together. Lower T3 on a low carb or carnivore diet does not automatically mean the thyroid is tanked. It may reflect a lower requirement for TV driven glucose metabolism, especially when less glycolysis is happening and there is less carbohydrate going through that pyruvate pathway. Reverse T3 is not just a waste product. It is part of the body's hormone relation system. You know, it's a regulation of the thyroid system. A metabolic break when the body decides that slowing down is appropriate. The brain is separate when it comes to thyroid hormone. It mainly imports T4 and then activates it locally into T3 using DiO two. So a standard blood T3 result does not directly tell you what T3 is doing inside the brain. An iodine is not simply a case of take more and pee out the rest. The kidney may excrete iodine, that's true, but the thyroid can still apply a protective shutdown when flooded with too much iodide. Different organs, different jobs. The urinary iodine test is useful because it can help show whether someone appears to need iodine in the first place. But it should not be used as an excuse for mega dosing. Measure first, then decide. So if you're looking at thyroid bloods don't look at T3 in isolation. Look at the full picture TSH 3T3 3T4 reverse T3 thyroid antibodies. Symptoms, body temperature, heart rate, energy, cognition, digestion, and the person's dietary context, especially if you're keto, carnivore or low carb. Because the question is not just is the number lower, the better question is. Is the system working? And that's the difference between pattern recognition and number chasing. And if there's one thing thyroid Twitter can do with, it's a bit of biology and less number chasing. So the thyroid is not a bucket, it's a precision instrument. And if you treat a precision instrument like a bucket, don't be surprised when it starts playing the bagpipes instead of the violin. So as always, this is Educational not personal medical advice. If you have symptoms or abnormal blood results, work with someone who understands the full thyroid picture and can interpret your results in the context of the way you eat and the way your lifestyle is. Anyway, hope that made sense. maybe no one's ever really talked about the brain T3 before, so it might be new to you. If you did enjoy that, make sure that you press the like button and subscribe and also comment if you want to. And if you share it, that will be fantastic too. if you have any comments on what else you'd like me to cover, then please drop that down below and I'll try and accommodate. If you're listening on Substack, thank you for listening on the Substack as well. I'm definitely not AI. I read this, that's why there's some mistakes. I don't edit the videos and I will see you on the next one. Thanks very much for listening. See you soon. I'll be back.