How to Control Your Metabolism by Thyroid & Growth Hormone

Andrew Huberman introduces himself as a professor of neurobiology and ophthalmology at Stanford School of Medicine and says the podcast is separate from his teaching and research roles there. The episode opens with sponsor reads for Four Sigmatic mushroom coffee, Blinkist and Munk Pack. In the Four Sigmatic read, he says lion's mane and chaga have been shown to have a slight anxiolytic effect, and that lion's mane lowered depression symptoms "just slightly" in several studies. He adds that he would not consider it a treatment for depression. In the Munk Pack read, he says he does not follow any one particular diet. His own routine is fasting early in the day, eating low carb during the day for alertness, and eating carbohydrates in the evening to aid the transition to sleep.

The episode belongs to a month-long series on hormones. Huberman argues that hormones shape development across the whole lifespan, not only in the womb or at puberty: "From the time you're conceived until the time you die, you are developing, you are changing." He describes two broad kinds of hormone action. One is an immediate effect, where hormones bind to cells and affect processes such as cell growth. The other is control of gene expression. He gives puberty as the example of the second kind, with changes in body hair, breast development, muscle, limbs and height.

Earlier episodes in the series covered testosterone, estrogen, insulin and glucagon. This one focuses on metabolism, mainly through thyroid hormone, growth hormone and related pathways. Huberman promises tools for raising or lowering thyroid hormone, because some people want to reduce it. He also promises tools for raising growth hormone, and notes that people rarely want to lower it. His stated aim is to give listeners an organizing logic they can use to judge hormone information from any source later on.

Before the main topic, Huberman answers a listener question about a claim he has seen online: that a food's shape shows which organ it benefits, such as walnuts looking like a brain or beets looking like a heart. He says he is "not aware of any science whatsoever" supporting this idea. He grants that some of these foods contain relevant substances. Beets contain arginine, which he says can control the dilation of blood vessels and arteries. Walnuts contain fatty acids that "maybe, I want to underscore maybe," benefit some aspects of brain health. Carrots contain vitamin A. His explanation for the myth is selection: people picked out foods that happen to resemble the organ a nutrient might support, even though many other foods supply the same nutrients.

the shape of things in the physical universe bears very little, if any, relevance to the nutrients that it contains and therefore the organs that it supports.

He then corrects himself on something from the previous episode. That episode covered emulsifiers in highly processed foods, which he said can strip the gut's mucosal lining and limit signaling from hormones like CCK that tell the brain to stop eating. In it, he had called Stevia an artificial sweetener. Listeners pointed out that Stevia is a noncaloric sweetener, not an artificial one, and he accepts the correction. Based on references listeners sent, he says Stevia does not appear to harm the gut microbiome, which seems unique among noncaloric sweeteners, though "There are probably others out there." He repeats an earlier point that Stevia can slightly raise blood glucose while slightly improving insulin management. Together, these probably cancel out unless it is consumed at very sweet concentrations. He adds that anything very sweet, caloric or not, triggers an insulin response, and that even the smell of a bakery can increase insulin secretion. He asks listeners to keep sending references.

Huberman notes that most people struggle with a metabolism that is too low or with keeping a healthy weight. A smaller group would like to slow their metabolism because they cannot eat enough to maintain their weight. He calls thyroid hormone and growth hormone, with their related pathways, "arguably" the two systems most significant for setting overall metabolism. He defines metabolism as the use of energy by the body's cells, not necessarily eating. That energy goes to growing tissue, repairing tissue and maintaining everyday function.

His main example of maintenance is the brain. He claims that most basal or resting metabolic needs go to thinking. Someone lying in bed all day and only thinking would use about 75% of their metabolic needs that way. Physical work, such as heavy labor or carrying children up and down stairs, burns more calories. Still, he says that unless someone is a marathoner or ultramarathoner, about 75% of their metabolic needs likely come from the brain, because neurons consume a lot of energy.

He therefore treats thyroid hormone and growth hormone as important beyond body fat and muscle. They also matter for repair after injury and for keeping cognitive function and clear thinking with age, including "offsetting dementia." He argues that a high metabolism, "provided it's not too high," tends to mean more bone and muscle and less fat. He declines to give target ratios, saying the numbers "are always shifting." His general comparison is that muscle and related tissue burn more energy than fat, and the body's water consumes none. As a result, adding muscle or reducing fat can raise metabolism.

Huberman presents a pattern he says applies to the hormones in this series. Neurons in the hypothalamus, at the base of the front of the brain, release what are called releasing hormones. He places the hypothalamus roughly a centimeter above the roof of the mouth and about a centimeter forward in most people. These neurons send axons into the pituitary. The pituitary then releases hormones into the bloodstream that usually carry the name "stimulating hormone," because they stimulate target organs.

Thyroid axis: thyroid-releasing hormone from the brain → thyroid-stimulating hormone from the pituitary → the thyroid releases thyroid hormones. Reproductive axis (from the earlier testosterone and estrogen episode): gonadotropin-releasing hormone from the brain → luteinizing hormone and follicle-stimulating hormone from the pituitary → the ovaries or testes. Growth hormone: the brain also contains growth hormone-releasing hormone.

Releasing hormone comes from the brain. Stimulating hormone comes from the pituitary.

He says that knowing a releasing hormone comes from the brain makes it "actionable in certain ways," and promises to return to this later. He describes the thyroid as a small butterfly-shaped gland near the Adam's apple. To find it, he suggests watching yourself in a mirror while swallowing water: "the thing that moves up and down, that is your thyroid." He says everyone has an Adam's apple whatever their sex or chromosomal background. It tends to be more pronounced in people who got a surge of testosterone early in development, because it is sensitive to testosterone, and this affects how deep the voice is. Behind the thyroid sit four small bumps, which he calls the parathyroid gland.

The thyroid releases two hormones, T4 and T3. Huberman says listeners can "basically forget about T4." He qualifies this: T4 is "not completely inactive" and has some roles, but T3 is the one that is "more or less active." He mentions the popular picture of hyperthyroid people as very thin with bulging eyes and hypothyroid people as overweight with half-closed eyes. He agrees that thyroid hormone does affect features of the face and eyes, as well as the amount of fat tissue.