Let's talk about brown fat. If you're willing, I'd love to drill into brown fat at a deep level. Again, my understanding of this is far more elementary than yours, obviously. You're the expert. My understanding about brown fat is that it's located in specific areas of our body, maybe more widespread than when I learned in school.

I was taught it was just at the clavicles and the back of the neck and upper back, but who knows? I learned that there's more of it when we're children, maybe more distributed throughout our body, and that it's rich in mitochondria. What is so special about the brown fat?

If we could just go into the biology of brown fat a little bit, what does it look like? You've measured it in human subjects. Where is it distributed really? Can it expand its distribution? Can we activate and expand the amount of brown fat as adults? For those of you that are cringing already thinking we're talking about getting fatter, it's quite the opposite.

We're talking about not subcutaneous fat, but fat located around the organs. Please educate me. Tell me where I'm wrong and expand my knowledge on brown fat. Okay. Yeah, you are not wrong, but it's true that there are more locations of the brown fat than we previously thought. There's this very nice study from 2017 by Leitner et al., where they had made these PET-CT overlays of their subjects, but you can see where in the body do we have brown fat and where can we grow more brown fat, so to say.

So the brown fat is very plastic, so it means that it can grow and it can decrease, and this is proven in studies where we have seen people with a failed cryocytoma, it's like a very specific cancer type, where from the '70s where we can see that if they have this specific kind of cancer type, they have this tumor on the adrenal gland, so they have like a huge increase in noradrenaline.

And because of that, they have this continuous activation of the brown fat. And they have grown a lot of brown fat in the whole body, abdomen, or where it's located in these six different places, but it is very much compared to normal people. And what they then see, what we learned from this study, is that brown fat can apparently grow if you have an increase in noradrenaline in the body.

It's not like you want that, because when that happens, you have a high blood pressure. You don't want it chronically, right? You just want it on a short amount of time, and then it can grow for a bit, but you don't want it chronically, of course not, because it activates also your sympathetic nervous system.

So they have also showed they have high blood pressure. They lost a lot of weight, of course, because this is activating your metabolism. So they found, luckily, that when they removed this benign tumor, that the brown fat decreases again to normal size, and they gained weight again, and they had normal blood pressure.

So the story ends well, but it's kind of like proof of concept of the brown fat can actually grow. So it's plastic in its way of like it can grow and it can decrease again. So that's very good, good studies to see what the body is capable of. But we don't, of course, want all that brown fat.

We just want it to be, we just want to keep it, actually, and keep it activated, because what we see in studies is also that after the age of 40, people, studies have shown that there is an association with having less brown fat, but increased obesity. So of course, we don't know yet whether brown fat decreases with age, and therefore we get obese or we get obese, and therefore we have less brown fat.

But as brown fat is an insulin sensitive organ in our body, and we get obese, just like the muscles get less sensitive, insulin sensitive, the brown fat does as well, and therefore it maybe decreases. It could be a theory that I think could be one of the reasons why we don't see that much brown fat in elderly people.

Some have a lot, especially people working outside, there are studies showing this. People who do physical work outside, farmers, and interesting. Yeah. They expose themselves to it, so they'll just keep it in that way. And I suppose we should clarify for people in case they don't know that insulin sensitivity is a very good thing.

You want that. You want your cells to be sensitive to insulin. Insulin insensitivity is type two diabetes, and is associated with obesity. So just a point of clarification there. Yeah. It's interesting to me. I usually work out at home, but I go to a gym once or twice a week if I can, because it's good if I see the outside world.

And there are a few individuals at the gym who, they're not particularly large or muscular, but they are incredibly lean, and their posture is great, presumably from the musculoskeletal work, and they're in their 70s and 80s. I mean, it's remarkable, right? And I know all the telltale signs of hormone augmentation.

I'm very good at spotting that. There are a few telltale signs. I've talked about this on other podcasts, and that's not why they're fit. They're clearly of that look, and you see this outside the gym too, of course, for people that look like they've done a lot of physical labor their whole life.

They're just moving a lot. They have strong hands and features, and they're not necessarily excessively lean, but you can tell that they've been using their musculoskeletal system. And I like to talk to these people and ask them, not what are you doing now for your workout, but what did you grow up doing?

And I would say, and obviously I haven't run statistics on this, but more than 75% of them respond that they grew up on a farm or that they did some sort of manual labor or were a postman or a postwoman or doing something where they moved a lot for their early years and throughout middle age.

And most of them are now in retirement, but some of them are still working and they all still moving a lot. So the relationship between shiver and brown fat makes sense to me, but is it the case that as we're just moving around, I've heard of NEAT, non-exercise induced thermogenesis.

So if we're just moving around, that we are activating brown fat, or does there need to be this stressor? Does there need to be shiver and a cold stimulus or a heat stimulus to activate the brown fat? In other words, is just staying active enough, or do we need to do some sort of temperature shock type thing like deliberate cold exposure?

Yeah, I think that is a really good question, because how, also why do we have this tissue? Then if it has to be extreme, then you can question what do we need this tissue for? But it seems that you can activate the brown fat with just a little bit of exposure to cold.

So cold is the most potent stressor activator of our brown fat because it's our temperature regulating organ in our body, so first responder to that. So the muscles will be a little bit too late, and therefore we have maybe these two kind of tissues. So actually just exposing yourself or a hand actually just to cold water.

So studies have shown that if you just put your hand in cold water, not that you're going to do that all day or every day or anything, it's not something you have to do, but it just shows that you can activate your brown fat just by getting a temperature change on your skin.

So you can go outside in a t-shirt, that's why also we were just talking about, well, people who works outside or move a lot or get in and out of it, like changing the temperature of their body all the time, they will have more brown fat and activating that is going to keep your metabolism higher and your insulin sensitivity, studies have also shown this.

So the brown fat can be activated as soon as you just change your temperature in the skin. So going outside in a t-shirt, wearing cooling vests, also studies have shown this for 10 minutes, it's going to also grow your brown fat. So you can get more brown fat if you expose yourself to the cold.

You don't have to start in a cold shower. You don't have to start in a cold plunge if you're not really ready for that yet. But just exposing yourself to the cold wind has also shown to activate your brown fat. Or if you don't want to be like in this awake state, then you can also just sleep in the cold and you won't notice it that much, maybe, but studies have shown that if you sleep in 19 degrees Celsius, then you will activate your brown fat and you will grow your brown fat.

So you have more of it. So this very nice studies from Hanson et al. from 2017 showed that a group of subjects who slept in a room at 24 degrees, and then they made this PET CT scanning to see how much brown fat do they have from the beginning, so what we call baseline.

Then they measured again after a month of sleeping in 19 degrees and they saw, I think it's remarkable, just one month at 19 degrees sleeping there. They had a duvet on and they were still had clothes on when they're sleeping. So they're under a cover, under a duvet. Under a duvet, yeah.

The subjects were sleeping at 19 degrees for one month, had increased insulin sensitivity. The next month they slept at 24 degrees, they measured this again and they had decreased actually a little bit, and then they slept at 27 degrees. So quite warm room actually for the fourth month and they saw even less activation of the brown fat and also insulin sensitivity.

So it seems that you can expose yourself and pretty rapidly the brown fat will respond to this because it's so sensitive to noradrenaline, right? So if you keep exposing yourself to a little bit of cold, you also get a little bit adapted to it, but that's because the brown fat has grown these more mitochondria in the cells.

So these small energy fabrics, that's going to activate the cells and that's going to take up glucose and fat from the fatty acids from the bloodstream to keep the thermogenesis up. And that's going to clear up some sugar and it's going to clear up in the bloodstream and some fat as well.

So the brown fat can in that way decrease our unhealthy fat, which is the white fat. And the white fat is what we don't want too much of, but we still need some, of course, and it's our energy storage. So it's very important that it's there. We just don't need a lot of it.

So on our thighs and also around our inner organs, that's where it's located. So if we can have activation of the brown fat just by going out in the cold and just by sleeping in a cold room, or if you have courage for it, you can go out and expose yourself in a cold plunge.

Cold showers is also going to do the trick. So you can do different variations of this. Just exposing yourself to various temperatures is going to activate the brown fat because it was involved to keep us in a perfect homeostatic balance regarding temperature. So to keep us alive.