If you thought body fat was just a passive storage depot for calories, think again. Research increasingly suggests that it plays an important role in our overall health, with two studies shedding new light on its complexity.

Fat exists in several forms. For instance, there’s white fat, which stores energy and releases hormones that influence metabolism; brown fat, which generates heat; and beige fat, which sits somewhere in between, switching on heat production under certain conditions. Even within these categories, location matters: fat under the skin is generally less harmful, while fat deep inside the abdomen – known as visceral fat – is strongly linked to inflammation, type 2 diabetes and heart disease.

The latest research adds further flesh to this picture, suggesting that fat, or adipose tissue, actively helps to regulate blood pressure and coordinate immune responses at key locations.

In one of the studies, at Karolinska University Hospital in Stockholm, Sweden, and her colleagues mapped the cellular architecture of visceral fat from multiple locations within the abdomen. They found that epiploic fat, which wraps around the large intestine, is unusually rich in immune cells, as well as specialised fat cells that produce inflammatory proteins associated with immune activation. Further experiments showed that microbial products originating in the gut trigger these fat cells to activate nearby immune cells.

“Our work shows that fat depots appear to be specialised according to their anatomical location, and those that sit right next to the intestine seem particularly adapted for immune interaction,” says Jalkanen.

Although the study involved people with obesity, Jalkanen suspects that epiploic fat serves similar core functions in people of all body weights, since everyone has some fat surrounding their intestine.

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“The intestine is constantly exposed to nutrients, microbial products and substances coming from our environment,” says Jalkanen. “Having fat tissue nearby that can sense, respond to, and help coordinate immune reactions could provide an additional layer of protection.”

In obesity, however, this system may become chronically overactivated. Eating too much, or too much of certain foods, and having particular bacterial compositions within the gut microbiome could potentially drive persistent immune signalling in intestinal fat, contributing to the low-grade inflammation linked to a range of metabolic conditions, such as type 2 diabetes and obesity.

The second study reveals another unexpected role for fat: controlling blood pressure. at The Rockefeller University in New York and her colleagues set out to understand why obesity, characterised by excess white fat, is linked to high blood pressure, while brown and beige fat appear to be protective.

They focused on perivascular adipose tissue, a fatty layer rich in beige fat calls that surrounds blood vessels. In mice genetically engineered to lose their beige fat, blood vessels became stiffer and overreacted to everyday hormonal signals that constrict arteries, leading to elevated blood pressure.

The team traced this effect to an enzyme called QSOX1, released by dysfunctional fat cells. Blocking it prevented blood vessel damage and normalised blood pressure in mice, regardless of their body weight. “What this nicely shows is that the communication between different organ systems is critical to understand complex diseases such as hypertension and blood pressure regulation,” says Koenen.

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“This study reveals an under-appreciated role for brown or beige fat,” says at The Ohio State University in Columbus. While deposits of perivascular adipose tissue are proportionately smaller in people than they are in mice, they are still probably physiologically relevant in us, she says. “[The study] emphasises a need for nuanced understanding of adipose impacts on health, independent of fat mass or body mass index (BMI) overall.”

The findings point to future therapies that focus less on simply reducing fat and more on preserving or restoring its beneficial functions by targeting specific fat depots, modulating immune-fat communication or maintaining healthy beige fat activity. However, any clinical applications would require further research.

Together, the studies highlight fat as an active, functionally diverse tissue involved in multiple aspects of human physiology. “When I started working in this field in the late 1990s, the prevailing view was that fat was just a simple bag of cells that stored excess nutrients,” says , also at The Rockefeller University, who was involved with the second study. “These studies illustrate a growing shift in the field: recognising fat not as a single cell type, but as a complex tissue with many different types of cells with different roles and diverse processes, extending well beyond just nutrient storage and mobilisation.”

Tiny fatty droplets in our cells are part of the immune system and help fight off bacterial infections. Until now the droplets were thought to be among the most vulnerable parts of the cell.

Lipid droplets are found in the cells of all complex organisms. They store fats and other lipids, which are essential nutrients. In humans, specialised cells called adipocytes store body fat in the form of lipid droplets.

For many years, biologists thought lipid droplets were “just an inert structure, just a storage site”, says Robert Parton at the University of Queensland in Australia. But in fact they also contain proteins, which carry out a wide range of functions. “We now have whole conferences looking just at the lipid droplets and all the associated processes.”

When a bacterium infects an animal cell, it often feeds on the lipid droplets. “It’s a nice source of fat inside the cell,” says Parton.

But it seems animal cells have found a way to turn the tables. “In retrospect, it sort of makes sense that in millions of years of battles between us and pathogens, the cell has also responded,” says Parton.

In a series of experiments on mice and on human cells, Parton’s team found that lipid droplets carry an array of proteins that are involved in the immune response. When dangerous bacteria enter the cell, chemical alarm signals are released, and these activate the immune proteins on the lipid droplets – which kill any bacteria that approach the droplet.

The cell has taken one of its most vulnerable components and weaponised it, says Parton. “It’s using it like a honey trap,” he says. “It’s producing these proteins, putting them on the lipid droplets, and then killing the bacteria.”

The evidence so far only shows that the lipid droplets can fight bacteria – there is no sign of them fighting viruses.

Furthermore, some bacteria can evade the lipid droplet attacks, and these are often pathogens we are familiar with. “We had Salmonella in there, and there was no killing as far as we could tell by this mechanism,” says Parton. It will be crucial to find out which bacteria can survive, and how they do so.

In the long run, Parton hopes to harness the immune activity of the lipid droplets to help treat infectious diseases.

“The ultimate is to be able to use this knowledge to combat the resistance of bacteria, and have it as part of our arsenal,” he says.