Essentials: How to Control Your Metabolism by Thyroid & Growth Hormone

**Andrew Huberman** (0:00)
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health and performance.
I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. This podcast is separate from my teaching and research roles at Stanford. It is however, part of my desire and effort to bring zero cost to consumer information about science and science related tools to the general public. Today, we are going to talk about two hormones, thyroid hormone and its related pathways and growth hormone and its related pathways, which arguably are the two hormones and two systems in the body that are most significant for setting your overall level of metabolism. So metabolism is the consumption of energy, not necessarily eating, but it's the use of energy in the cells of the body for growth of tissues, for repair of tissues, and also just for day to day maintenance of function. These two hormones, thyroid hormone and growth hormone, we think of as related to metabolism of things in the body, keeping body fat low and keeping muscles strong and tendons strong and repairing themselves, et cetera. But they are also key for brain function, for the ability to maintain cognitive function throughout the lifespan. So, the big theme I'd like to introduce is that metabolism isn't just about losing weight, but having a high metabolism, provided it's not too high, is great. It means that you will have more lean tissue, more bone and muscle and less adipose tissue, fat. And we know that that's healthy. There are neurons in your brain in an area called the hypothalamus, which just means it's below the thalamus, hypo. It sits at the base of your brain in the front, it's part of the forebrain. So it's more or less above the roof of your mouth, maybe about a centimeter or so, and then about a centimeter forward in most people. And neurons in the hypothalamus release hormones that are called releasing hormones. So anytime you hear releasing, chances are those are neurons that are in your brain and they extend little wires, we call axons into your pituitary. And the pituitary releases a bunch of hormones into the bloodstream and the pituitary releases things that most often have the name of stimulating hormone because they stimulate organs. So in keeping with the theme of thyroid hormone, you have thyroid releasing hormone in the brain, tells the pituitary to release thyroid stimulating hormone. And then the thyroid, which we'll talk about in a moment, releases thyroid hormones. The thyroid is a little butterfly shaped gland that's right around the Adam's apple. And it's got four little bumps behind it called the parathyroid gland. And it releases two hormones into the blood to stimulate different tissues and their metabolism. And those hormones are called T4 and T3. So if this is already sounding like a lot of information, it's really easy. I promise. Releasing hormone comes from the brain, stimulating hormone comes from the pituitary. And in this case, we're talking about the thyroid binding up that stimulating hormone and saying, oh, I need to release something. And it releases T4 and T3. And guess what? You can basically forget about T4. T4, it's not completely inactive. It has some roles, but T3 is the one that's more or less active. Now, what does thyroid hormone do? The main role of thyroid hormone of T3 is to promote metabolism. And that doesn't just mean the consumption of energy. It means the utilization of energy, including the buildup of tissues. So it acts on all sorts of target tissues in the body. It acts on muscle, it acts on the liver, it acts on the cartilage, it acts on the bone. It's involved in taking fats and breaking them down into fatty acids and converting those into ATP, which is an important thing for cells to use energy. It's also involved in taking sugars and turning those into energy. And yes, it goes to adipose tissue to fat. We have different kinds of fat that we'll talk about today, but it goes to white fat and it liberates or helps liberate some of the fats from those fat cells and use them for energy. And this is why higher thyroid is associated with leaner bodies. Lower thyroid is associated with less lean bodies. One thing that's absolutely key and is actionable, we're right there already in discussing tools, is iodine. Iodine is most common in sea salt, in kelp, and in seaweed. And most people can get enough iodine from the food they eat and or the table salt they consume. Almost all table salt from all over the world, regardless of where you are, contains iodine. The thyroid needs iodine in order to produce thyroid hormone. Iodine combines with an amino acid that we've talked about before called L-tyrosine. L-tyrosine comes from meat, from nuts. There are some plant-based sources as well. It is the precursor to dopamine. But in the thyroid, iodine combines or works with L-tyrosine to produce T3 and T4, the thyroid hormone. So you absolutely need sufficient iodine. You need sufficient L-tyrosine. And then you also need something else, which is called selenium. Selenium is important in order for thyroid hormone to be made because of the way that it allows L-tyrosine and iodine to interact. And the thing is most people aren't getting enough selenium because they don't eat foods that are high in selenium. Now, how much selenium you need will depend on where you live. It actually varies country by country. Some countries I found say that you should get 100 micrograms. Some say 200, some say 155 The average was about 155 micrograms. The countries I looked at, people who are trying to increase thyroid levels might want to consume more selenium. And if you consume a vitamin, of course, you want to make sure if it has selenium, that you're not overdoing it by consuming a lot of selenium rich foods either. Brazil nuts are the heavyweight champion of foods to get selenium from. It has very high concentrations of selenium. In just six or eight Brazil nuts contain something like 550 micrograms of selenium. It's also present in fish, ham of all things, contains a lot of selenium for whatever reason pork does. I'm not a big consumer of pork. Beef has some selenium, but what's interesting if you look at the sources, pork, beef, turkey, chicken, cottage cheese, eggs, brown rice, what you want to understand is that they have something like 30 to 50 micrograms of selenium. So if you're not eating Brazil nuts, and I'm guessing most people aren't, then and you're not eating a lot of animal based foods, which I know many of you aren't, then you're probably not getting enough selenium. And again, you can have these levels measured or you can just check what you're consuming and figure out whether or not you're meeting the ration that you need in order to get healthy levels of thyroid. I also want to mention that for children, their daily requirements of selenium are much lower, as low as 30 or 40 micrograms for kids 14 years or younger. And again, that's micrograms, not milligrams. So again, look into what you need. But if you're somebody who's interested in keeping thyroid function healthy and productive, then you certainly want to make sure you're getting enough iodine, you're getting enough selenium, and you're getting enough l-tyrosine. And it's interesting when you start looking at the various foods, especially highly processed foods, then you start to realize that perhaps many people, maybe you, are not. I'd like to take a quick break and thank our sponsor, 8Sleep. 8Sleep makes smart mattress covers with cooling, heating, and sleep tracking capacity. Now, I've spoken before on this podcast about the critical need for us to get adequate amounts of quality sleep each night. Now, one of the best ways to ensure a great night's sleep is to ensure that the temperature of your sleeping environment is correct. And that's because in order to fall and stay deeply asleep, your body temperature actually has to drop by about one to three degrees. And in order to wake up feeling refreshed and energized, your body temperature actually has to increase about one to three degrees. 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