Fat surrounding the colon interacts with the immune system

Abdominal fat is not a uniform tissue. A new study from Karolinska Institutet, Steno Diabetes Center Copenhagen, and Helmholtz Munich reveals that fat located close to the large intestine contains an unusually high number of inflammatory fat cells and immune cells. The findings suggest that this tissue is specially adapted to communicate with the immune system in the gut region. The study is published in the journal Cell Metabolism.

In the study, researchers mapped five different abdominal fat depots in individuals with severe obesity. The results show clear differences between these depots. Most striking is the so-called epiploic fat tissue along the colon, which contains numerous fat cells linked to inflammation as well as a substantial presence of immune cells.

Laboratory experiments demonstrated that bacterial signals can prompt fat cells to produce proteins that activate immune cells within the tissue.

“Fat tissue doesn’t just store energy – it also functions as an active organ, sending signals that affect the entire body. A common misconception is that abdominal fat is uniform, when in fact it consists of several distinct depots,” says Jiawei Zhong, PhD student at the Department of Medicine, Huddinge, Karolinska Institutet, Sweden, and co-first author of the study.

Adaptation to the gut microbiome

Taken together, the results indicate that fat tissue near the gut has a unique function. The researchers believe this may be an adaptation to the gut microbiome – the bacteria and other microorganisms that are a source of inflammatory substances. Since the study was conducted on individuals with obesity, it remains unclear whether the findings apply to people of normal weight, and any direct clinical implications have yet to be established.

“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. Now that we know it contains both fat cells and immune cells, we want to investigate how their interaction influences disease activity. Our goal is to find out whether this fat tissue contributes to amplifying or sustaining inflammation by sending signals that affect immune cells locally,” says Jutta Jalkanen, researcher at the same department and co-first author of the study.

The study was carried out in collaboration with Helmholtz Munich, Germany, and Steno Diabetes Center Copenhagen, Denmark. It was funded by, among others, the Swedish Research Council, the Novo Nordisk Foundation, ERC, and the Knut and Alice Wallenberg Foundation. Some researchers have received fees from pharmaceutical companies, as disclosed in the scientific article.

Publication: “Cytoarchitectural multi-depot profiling reveals immune-metabolic crosstalk in human colon-associated adipose tissue”, Jutta Jalkanen, Jiawei Zhong, Pamela A. Nono Nankam, Nayanika Bhalla, Merve Elmastas, Jiaxin Luo, Sophie Weinbrenner, Scott Frendo-Cumbo, Benedek Pesti, William Gourash, Anita Courcoulas, Zinger Yang Loureiro, Arne Dietrich, Jesper Bäckdahl, Anders Thorell, Marcus Buggert, Joanna Kalucka, Margo P. Emont, Evan D. Rosen, Matthias Blüher, Peter Kovacs, Patrik L. Ståhl, Lucas Massier, Mikael Rydén and Niklas Mejhert, Cell Metabolism, online 13 January 2026, doi: 10.1016/j.cmet.2025.12.008.