Not all abdominal fat behaves the same way. A new study suggests that fat tissue located next to the colon may play a distinct role in immune signaling and inflammation, particularly in people with obesity.
Researchers from Karolinska Institutet, working with colleagues at Steno Diabetes Center Copenhagen and Helmholtz Munich, analyzed human abdominal fat tissue from individuals with severe obesity. They found that fat surrounding the large intestine contains unusually high numbers of inflammatory fat cells and immune cells, setting it apart from other abdominal fat depots.
The study was published in Cell Metabolism.
Abdominal fat is often discussed as a single category, but the researchers mapped five distinct fat depots and found clear biological differences among them. The most striking differences appeared in epiploic fat, the tissue that lies directly along the colon.
Laboratory experiments showed that bacterial signals can prompt fat cells in this tissue to produce proteins that activate nearby immune cells. This suggests that fat near the gut is not just storing energy but actively participating in immune communication.
“Fat tissue doesn’t just store energy — it also functions as an active organ, sending signals that affect the entire body,” said Jiawei Zhong, a PhD student at Karolinska Institutet and co-first author of the study. “A common misconception is that abdominal fat is uniform, when in fact it consists of several distinct depots.”
The researchers believe this immune-active fat may represent an adaptation to the gut microbiome. The colon is home to trillions of bacteria that can release inflammatory signals, and fat tissue in this region may be uniquely equipped to respond to that environment.
Because the study focused on people with severe obesity, the authors caution that it remains unclear whether the same fat tissue characteristics are present in people of normal weight. The findings also do not establish direct clinical implications.
“The next step is to understand the role of fat tissue around the colon in inflammatory bowel diseases such as Crohn’s and ulcerative colitis,” said Jutta Jalkanen, a researcher at Karolinska Institutet and co-first author of the study. “Now that we know it contains both fat cells and immune cells, we want to investigate how their interaction influences disease activity.”
The researchers emphasized that the work is exploratory and intended to deepen understanding of how fat tissue, the gut and the immune system interact. Further studies will be needed to determine whether this immune-active fat contributes to disease progression or could eventually become a therapeutic target.
The study was supported by public and foundation funding focused on metabolic health, immunology and biomedical research. Funding sources included the Swedish Research Council, the Novo Nordisk Foundation, the European Research Council, and the Knut and Alice Wallenberg Foundation. Some study authors reported receiving fees from pharmaceutical companies, as disclosed in the scientific publication.