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THE VITAL, OVERLOOKED ROLE OF BODY FAT IN SHAPING YOUR HEALTH AND
MIND  
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Linda Geddes
November 17, 2025
New Scientist
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_ The discovery that fat is a communicative organ with a role in
everything from bone health to mood is forcing a rethink of how we
view our bodies _

, Matt Dartford

 

If you melted down the average UK adult, you’d find around 22
kilograms (48.5 pounds) of creamy yellow fat – equivalent to around
88 blocks of lard, enough to fill two-thirds of a small suitcase or
cast into 446 dinner candles. Melted, it would easily be enough to
paint a large bedroom in a translucent, waxy sheen.

It’s a queasy thought. For centuries, we’ve regarded body fat as
an inert, lard-like substance. We carry it everywhere, and frequently
despise it – yet this pale, oily tissue is undergoing a radical
reassessment. Far from an inert nuisance, it is an organ – one that
is alive and surprisingly communicative, has its own memory and is
capable of influencing everything from appetite and metabolism to
fertility, mood and immunity.

Fat, it turns out, isn’t one thing. It comes in white, brown, beige
and even pink forms – each with distinct functions and found in
different locations – and contains a mix of immune cells, nerves and
blood vessels that contribute to its powers.

“You wouldn’t get pushback today if you claimed fat was an organ,
in the same way your lungs or liver or spleen are organs,” says Paul
Cohen
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at The Rockefeller University in New York, who researches metabolic
disease and cancer related to obesity. This shift in thinking is
reshaping our view of body fat and our understanding of obesity. It
challenges how we think about trying to get rid of fat, and is even
prompting some scientists to explore how to reprogram it instead –
not just to tackle obesity, but to improve our broader health.

Until relatively recently, body fat – also known as adipose tissue
– was largely seen as a passive storage depot for excess calories, a
layer of insulation against the cold and simple padding. These
functions are clearly important: the evolution of body fat may have
aided humans in moving out of Africa and surviving in colder climates.
Even today, carrying a bit of excess weight reduces the likelihood of
older people dying if they fall ill.

“I think the first thing that people fail to appreciate is what a
valuable evolutionary step it was to be able to store fuel,” says
Randy Seeley,
[[link removed]] who
researches energy balance and metabolism at the University of
Michigan. “If you’re not able to do that, you’re a filter
feeder: you have to swim in your food.”

But while many organisms possess some form of body fat, in mammals, it
has evolved into something much more complex than just a kind of meaty
bubble wrap, says Seeley. “It also now becomes integrated into the
overall regulation of blood glucose, body temperature and other
physiological functions, including bone health.”

CONTROLLING HUNGER

The first clues that we were underestimating our body fat came in the
1990s with the discovery of leptin
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This hormone, secreted by fat cells, acts on the brain to suppress
appetite and boost energy expenditure. On the flip side, when people
quickly lose fat, leptin levels drop, which the brain interprets as a
sign that energy stores might be running low. It responds by ramping
up hunger signals and reducing energy expenditure to help you regain
that lost fat.

The discovery of leptin cracked open a hidden communications network
between fat and the rest of the body. Since then, we have discovered
that fat cells release many more hormones and other signalling
molecules, some of which communicate with tissues nearby, while some
travel much further afield. Together, they are known as adipokines.

What’s more, this communication isn’t only chemical – it’s
also electrical. We now have evidence for networks of nerve fibres
extending deep inside adipose tissues, forming a direct, two-way line
of communication between the brain and our fat.

“The nerve supply in adipose tissue enables a bidirectional and fast
communication route with the brain,” says Kristy Townsend
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a neuroscientist at The Ohio State University who studies fat. As well
as sending messages about energy and metabolism, nerves allow fat to
quickly communicate its health status, for instance, whether it is
injured or inflamed.

FAT AND IMMUNE HEALTH

Immune cells may also join these conversations, relaying information
about inflammation or injury and releasing molecules that help nerves
survive and grow. “If you look at the tissue in between all the
adipocytes, there’s pretty much every immune cell you can imagine
– so fat is also an immune organ,” says Townsend.

In short, fat doesn’t just store energy; it speaks. And together,
these adipokines, immune cells and nerve fibres form the vocabulary of
an unexpectedly sophisticated organ.

The far-reaching impacts of fat are only now coming to light. Its
best-documented role is in energy balance (see “Your unappreciated
organ”, below), telling the brain when reserves are full or
depleted. But fat’s communication with the brain also seems to
extend to our moods. While mood disorders such as depression or
anxiety are complex, and stigma or poor body image may also contribute
to this, evidence is increasingly linking obesity – particularly
metabolically unhealthy obesity – to these conditions.

While the mechanisms are still under investigation, the leading idea
is that inflammation within adipose tissue triggers brain inflammation
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which in turn alters the balance of neurotransmitters and triggers
behavioural changes. Altered levels of leptin may also influence brain
reward circuits and mood regulation.

And our fat plays a crucial role in fertility, too. Without a minimum
level of body fat, for example, menstruation won’t start or will
stop, which makes sense, because entering pregnancy without sufficient
energy to sustain a developing fetus could be catastrophic for both
mother and child.

“People forget that fat is metabolically really important. Without
fat, we have issues with hormonal control, infection immunity,” says
Louise Thomas
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a professor of metabolic imaging at the University of Westminster in
London.

WHEN FAT TURNS BAD

So if fat is such a crucial factor in our health, why does it get such
a bad rap? The first issue is its location. White fat makes up more
than 95 per cent of our total stores and is found both under the skin
(subcutaneous fat) and wrapped around internal organs (visceral fat).
“Our organs are often sitting in a sea of fat,” says Thomas.

That internal sea can turn toxic. Excess visceral fat
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is linked to a higher risk of type 2 diabetes, high blood pressure,
heart attacks and certain cancers. Growing evidence also suggests it
may affect brain function
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and contribute to conditions such as Alzheimer’s disease.

What triggers this shift from cooperative organ to rogue state is a
major focus of research. While white fat cells in both subcutaneous
and visceral deposits can expand and contract depending on the
body’s storage needs, those surrounding internal organs appear
especially vulnerable to the harmful effects of excess fat.

In obesity, these fat cells enlarge and are prone to dying once they
reach a critical size. Part of the problem is that their blood supply
can’t keep up with their growth. Stressed and suffocating, they
release inflammatory molecules as distress signals, attracting immune
cells to clear dead or dying cells.

These immune cells intensify the inflammation, with effects reaching
far beyond the fat itself. The chemical signals interfere with insulin
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regulates blood sugar – raising the risk of type 2 diabetes. They
are also linked to cognitive changes seen in obesity such as memory
and attention problems, and may create conditions that foster tumour
growth. Obesity is a risk factor for many kinds of cancer
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and often people who are obese tend to have worse outcomes.

Dying or overstuffed fat cells also release fatty acids, or lipids,
into their surroundings – and in excess, these can be toxic to
surrounding cells. Over time, this lipotoxic stress can damage the
network of nerves threaded through fat, a condition known as adipose
neuropathy [[link removed]].
Obesity, type 2 diabetes and ageing are all linked to this loss of
peripheral nerves, which further disrupts metabolism by impairing
communication between the brain and fat.

PROTECTING BONE HEALTH

Misfiring fat signals can also play havoc with our bones. Most of the
time, oestrogen produced by adipose tissue can help protect against
excessive bone resorption – where old bone tissue is broken down
faster, then new bone can replace it. However, growing evidence
suggests that excess fat, particularly visceral fat and fat
accumulation within bone marrow, can impair bone quality and increase
fracture risk. This is partly because inflammatory cytokines released
by adipose tissue can stimulate osteoclasts, the cells responsible for
bone resorption, which, in turn, promotes bone loss
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Despite the downsides of dysfunctional fat, adipose itself isn’t the
enemy – we need it. And efforts to get rid of it can backfire.
Studies of liposuction
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procedure that removes targeted fat, suggest that the extracted fat
may simply reappear elsewhere. “You may want to remove fat from some
locations, but you may like even less where you get it afterwards,”
says Seeley, who has been involved in some of this research. “If you
remove subcutaneous fat, you’re probably going to end up with more
visceral fat in the long run, and that probably leaves you in a worse
place than where you were before.”

Not everyone with obesity is unhealthy, either. Between 10 and 30 per
cent [[link removed]] of people
classified as obese based on body mass index seem to escape the usual
health effects, such as insulin resistance, high blood pressure and
unhealthy cholesterol levels – at least in the short term. This
so-called metabolically healthy obesity has intrigued researchers like
Matthias Blüher
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at the University of Leipzig in Germany.

About 15 years ago, Blüher and his colleagues began comparing fat
tissue [[link removed]] from people with
obesity who developed insulin resistance – often a precursor to the
development of type 2 diabetes – and those who didn’t. They found
that where excess fat sits and how it behaves are both crucial: people
with more visceral and liver fat tended to be metabolically less
healthy, while those whose adipose tissue contained smaller fat cells,
fewer immune cells and a healthier secretion pattern of adipokines
appeared to be more protected.

DIFFERENT TYPES OF FAT

More recently, the researchers have taken this investigation down to
the cellular level, analysing which genes are active in different fat
deposits across dozens of people with healthy and unhealthy obesity.
Their results, published earlier this year, reinforce that not all
visceral fat is equal
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“Even within the visceral cavity, it makes a difference where the
fat is located,” says Blüher. The highest risk is associated with
fat that sits outside of the intestine, although, for now, they
aren’t sure why this is the case.

The fat also looks different in people with healthy obesity: their fat
cells are more metabolically flexible – able to switch efficiently
between storing and burning energy – pump out fewer inflammatory
signals and host fewer immune cells. Their visceral fat also contains
mesothelial cells, which can transform into other cell types, perhaps
enabling their fat to expand more smoothly without triggering
excessive inflammation. Why some people have more of these
metabolically healthy cells is probably down to genetics, although
lifestyle factors such as diet and exercise may play a role.

Either way, Blüher thinks that these insights could help doctors
identify which people with obesity are at the highest risk of
complications, and then tailor treatment accordingly.

REPROGRAMMING FAT FOR HEALTH

His longer-term dream is to find a way to restore fat’s healthy
function – perhaps even transform “unhealthy” obesity into a
permanently more benign form. Encouragingly, this may not require
dramatic weight loss. Many of the benefits of modern weight-loss drugs
and bariatric surgery seem to stem not from the amount of weight lost,
but from improving fat distribution and function, says Blüher. “In
bariatric surgery, even if people don’t lose a lot of weight, the
health benefits start almost immediately.”

Achieving this would be revolutionary, not least because it would
prompt a rethink of what a healthy body shape looks like.

And if fat could be reprogrammed to behave more healthily – or the
cellular memories of its bloated heyday erased (see “The yo-yo
effect”, below) – many more of us might live longer, healthier
lives without obsessing over size.

Whether obesity begins in the adipose tissue or the brain is still
debated, but it is clear that when communication between the two
falters, the whole system drifts off-kilter.

Seeley likens the situation to an orchestra: “All of these organ
systems – your liver, pancreas, adipose tissue, muscle and
gastrointestinal tract – are all talking to your brain, and your
brain is talking to all of them. If your symphony conductor isn’t
doing a good job, then even if all your instruments are OK, it won’t
sound great.”

In other words, fat isn’t necessarily the problem; it’s an
instrument playing slightly out of tune in a misdirected symphony.
Many of us have been conditioned to try to shrink, remove or hide our
body fat. But the real task is to understand it – to coax this
creamy, talkative organ back into harmony with the rest of the
orchestra. Because when it plays well, it helps keep the whole body in
tune.

_Linda Geddes_ [[link removed]]_ is a Bristol-based
journalist writing about biology, medicine and technology. Born in
Cambridge, she graduated from Liverpool University with a first-class
BSc in Cell Biology. She spent 3.5 years at The Guardian as a
science correspondent, including during the COVID-19 pandemic, and
remains a regular contributor. Prior to this, she spent nine years
at New Scientist magazine working as a news editor, features editor
and reporter, and co-presented of the BBC World Service podcast
Parentland, as well as various science documentaries for BBC Radio
4. Linda has received numerous awards for her journalism, including
the Association of British Science Writers’ award for Best
Investigative Journalism. She has also published two books:
Bumpology, the myth-busting pregnancy book for curious parents-to-be,
and Chasing The Sun, the new science of sunlight and how it shapes our
bodies and minds._

_New Scientist_ [[link removed]]_ is the
world’s most popular weekly science and technology publication. Our
website, app and print editions cover international news from a
scientific standpoint, and ask the big-picture questions about life,
the universe and what it means to be human. If someone in the world
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_Since the magazine was founded in 1956 for “all those interested in
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York, with operations elsewhere in the UK, the US and Australia._

 

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