The truth about fat, and its complex role in our health

This is the Guardian.

0:00

When it comes to our bodies, there's one part that has been more maligned, stigmatized, and misunderstood than any other fat. For a long time, it was simply seen as an inert yellow substance wrapping around us. But that idea is changing. Scientists are beginning to understand that our fat is actually intricate and dynamic, constantly in conversation with the rest of our body. It's now considered by some to be an organ in its own right. So today, the truth about fat and the complex role it plays in our health. I'm the Guardian science editor, Ian Sample, and this is Science Week Weekly. So, Maddie, we're asking, is body fat really so bad? But before we get to the pros and cons, start me off with the basics, like what is fat?

0:11

So, the biological term for fat is adipose tissue, and it's a connective tissue, which is basically the body's structural support. And it's found all over the body. There's a layer in between the skin, skin and the muscle, and that's called our subcutaneous fat. And that's the fat that you would, I guess, in a way, you see, and then you have visceral fat, and that sits between and around your internal organs, and it cushions them and it helps hold them in place. It's also actually inside our bones. And its function there is slightly less clear than in other parts of the body.

1:19

So we have these two types of fat, the visceral fat, which sort of wraps around our organs, and the subcutaneous fat, which is, as you say, the stuff we might notice more easily on our bellies or thighs. But within those, there are also different types of fat which sort of shift about over the course of our lives. Tell me about those.

1:56

The first one is white fat, and I think that's the fat of popular imagination. And this is our main energy store, and it's the biggest proportion of fat in our body.

2:17

The.

2:27

Then you have brown fat, and that tends to be found in much smaller amounts. And brown fat is all about thermoregulation. And what it does is it converts calories into heat when we're cold. The way that it does that is brown fat cells have a lot of mitochondria, and it's especially important in newborns because newborns, obviously, they're not very big, and they're not big enough to shiver. And so brown fat is really important for them, for their temperature control. As you age, the proportion of brown fat to white fat reduces. And so in adults, you don't have that much. It's Difficult to measure accurately, but it's been estimated at less than 0.5% of total body mass. And then you have beige fat. Now, beige fat is, I guess, a mix of white fat and brown fat. These are intermediate cells that are peppered through white fat. And beige fat cells can be triggered to behave like brown fat.

2:27

We tend to think about fat from an external perspective, I suppose, but what's it up to in the body?

3:26

Okay, as I said, brown fat, it's for producing heat, it's insulation, it's a protective cushion for joints and bones and our internal organs. But it does have a lot of other roles as well. And I spoke to Professor Declan o', Regan, British Heart Foundation Chair of Cardiovascular AI, a Medical Research Council investigator and consultant radiologist.

3:32

It's too easy to think of fat just as this inert tissue that's kind of sitting there as a store of energy. It's actually a very dynamic tissue and affects the whole body. It's a whole ecosystem in itself, in many ways that senses things about the body, that senses nutrients, that senses other factors and also influences things. It releases hormones, it releases signaling molecules, it affects appetites, blood pressure, how we manage our blood sugar. It's also really important for inflammation as well as.

3:58

And so adipose tissue, it's not some passive stuff sitting there waiting to be used. It's communicating with the rest of the body through hormones and chemical signals. And it's even got a nerve supply that allows two way communication with the brain is super, super complex, which is why now actually it's very often referred to as an organ rather than tissue.

4:28

So you've talked about why fat is so much more than just this inert tissue. We might think of it as, but why is too much of it bad for us? How does this critical organ sort of turn on us?

4:54

The direct impact of extra weight is the mechanical ones, so it can put stress on your joints. It can also affect sleep. You're more likely to have sleep apnea if you're carrying extra fat around the airwaves. And that disrupted sleep has knock on effects for the rest of your health. It can lead to high blood pressure because the heart has to pump harder to get the blood around the body. And Declan described some other things as well.

5:05

As fat becomes more excessive or starts to shift to unhealthy places in the body, it starts to drive things like chronic inflammation, us becoming more resistant to insulin. And also one thing that we're interested in is it starts to accelerate the rate at which we age as well.

5:35

So Declan mentioned aging there, which is really interesting. What's happening there?

5:51

Yeah. So Declan wanted to understand how and why people age at different rates. So he took some data from the UK Biobank. So this is this incredible resource of 500,000 people who have shared their DNA and had their brains and bodies scanned for scientific purposes. And he was interested in people's age gap. So that's the difference between their actual age and their biological age. He was specifically interested in the cardiovascular system. And with this subset of people from the biobank, he found that visceral fat, so that's the fat that's stored around your organs, was one of the most important indicators for driving this accelerated aging of the heart and the circulatory system. And I asked Declan why that was, and he explained to me that it's really all about inflammation.

5:56

So there are immune cells that are sitting in normal visceral fat anyway, but due to overnutrition, as that visceral fat starts to expand, those cells become stressed. So the oxygen level kind of falls. They start pumping out these pro inflammatory chemicals. These flood the bloodstream with these sort of warning chemicals, right, that then circulate to the liver and then the rest of the body. And this causes this chronic low grade inflammation throughout the body. And we know that that promotes a kind of response in other tissues, where in the heart, for instance, you tend to get stiffening of the heart muscle in the large blood vessels as well, you get fibrosis and the heart becomes smaller and stiffer, the blood vessels become stiffer, and it affects other organ systems as well. It also starts to contribute towards diabetes. And actually, if we measure a chemical in the blood called glycay, Glycase, a really exciting chemical that gives like a barometer of how much inflammation is going on in the body. We can see as people start to put on weight, then these inflammatory markers start to go up. And this is all being driven by the visceral fat responding to the stress of excess nutrition and sending out these chemicals into the body that are harmful.

6:51

Okay, so Maddie, we have this relationship between visceral fat and a prematurely aging cardiovascular system. But what about fat in other places? The hips and thighs, for example, Is there any relationship there with health?

8:09

So this is where the difference between men and women, generally speaking, comes in. Subcutaneous fat in men and women, it tends to be round the middle for men and the hips and thighs for women. Interestingly, it's thought that oestrogen has a role in determining this difference. And it appears like there's a genetic factor involved. So some women tend to get more fat on the hips and the thighs than others, even with the same diet and exercise. And fat on the hips and thighs seems to be, in fact, in comparison to the visceral fat, protective rather than detrimental to your health. Declan and his team looked at this effect in women because it is a typically female fat distribution.

8:24

We found out that women's body fat distribution when it's on the hips and thighs is protective. And particularly women who are actually genetically predicted to have more fat around the hips, they seem to have younger hearts compared to women who weren't genetically predicted to have this sort of distribution.

9:10

Are there any ideas as to why fat on the hips and thighs is protective?

9:30

There isn't a lot of evidence around this. It might be that it being there keeps fat away from the more dangerous places, which I mean basically proximity to your organs. But Declan did offer another idea for why female pattern fat distribution could be protective.

9:35

Fat, again, it's not inert, it's actually secreting factors as well called adiponectins which circulate around the body. And we think some of those are anti inflammatory, so they may counteract the effect effects of fat in other places. So we only really found that pattern as well in premenopausal women. So it may be that after the menopause when estrogen drops down, that some of these effects are lost. So it could be a pointer towards HRT actually continuing that protection, if you like, after the menopause.

9:56

Coming up. Why the relationship between fat and health is more complex than it seems. Okay. So for women at least there is evidence that fat can be somewhat protective depending on where it is on their bodies. And this points to the complex relationship between fat and health. Right?

10:28

Exactly. It's really not simple at all. I mean, when you're looking at population level data, it's very difficult to find definitive causes of disease or ill health. Health. People who have obesity might be more likely to also do things or be affected by things that actually are the real underlying contributor to the ill health. So pollution, smoking and drinking, stress, lack of access to healthy food, and being able to say, oh, actually it's the fat in of itself that is causing the disease is really very, very tough. And there are even more complex things going on. Like people who have obesity might more likely to receive poor health care because they might go to their doctors and always be told, oh well, you need to lose weight and actually another underlying issue gets ignored. Or the mental health impacts of having obesity. You know, we live in a very fat phobic society. And, you know, for a long time people have observed that it's possible to have excess adipose tissue and be perfectly healthy. It's this idea of fat but fit. And I did actually ask Declan about this concept.

10:55

One thing we did look at was the effect of exercise. So we did find that people who were fit tended to be a bit more resilient to the effects of visceral fat. But visceral fat is bad for everyone. Even if you're super fit, then visceral fat still adds on years to your heart age.

12:11

So how do you know if the amount of fat you have is going to be damaging for your health?

12:29

Well, going back to where the fat is, you can't know this unless you have a fancy MRI scan that are really only done in hospitals. If you go to the gym and you're, you know, you stand on one of those machines that tells you your sort of body fat percentage, they're not very accurate, so you won't necessarily get a good idea from that. And it's tricky as well because a lot of the sort of more basic tools that we use, like calculating bmi, they're also not great indicators for health because they often don't take into account where the extra weight sits or it doesn't take into account whether the weight is fat or muscle. So very often people with above average muscle mass can appear to be overweight when they're measuring their bmi. One way to get at it is to calculate your waist to height ratio or your waist to hip ratio. And that can help you understand if you might have a bit more visceral fat. But there's, there's no perfect way of doing this.

12:34

So the question on everybody's minds is going to be, how do you get rid of that bad kind of fat?

13:39

I'm sure a lot of us might have gone to the gym and thought, I'll just do some sit ups. But maybe speaking from experience, that's not going to work because you can't just specifically target visceral fats. You have to look after your general health. Another route that some people might want to take, liposuction. Interestingly, with liposuction, some studies that have been done have found that liposuction doesn't give you any of the health benefits that you would get losing the equivalent amount of adipose tissue. And there's studies as well that suggest that if you have liposuction and remove this subcutaneous fat, it could come back in different places and places you might not want it. And so, as I said, it's all about trying to look after your general health. But the problem is we live in an obesogenic environment. It is really, really tough. And fat is also very complicated. I mean, you see that with these weight loss drugs that people lose weight really, really quickly. But the evidence seems to be pointing towards now that when you come off them, you can gain that weight back pretty fast. So, I mean, nobody has been able to solve this question. All this research has shown me that we actually really need to think about fat differently. We need to kind of have a different concept of it because it's so despised and derided and we can hate ourselves for it. And this is a super complex organ that is doing incredible things in our body and it's communicating with the rest of our body. And I think the more we learn about it and the more we can understand how this organ is interacting with our health and our aging, the better we can learn to love and live with it in a healthy way.

13:45

Hear, hear. Thanks very much, Maddie.

15:51

Thanks, Ian.

15:53

Thanks again to Madeline and to Professor Declan o'. Regan. And that's all from us today. This episode was produced by Ellie Sands. The sound design was by Joel Cox, and the executive producer is Ellie Burey. We'll be back on Thursday. See you then.

15:58

This is the Guardian.

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