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, 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.
“Our study shows that fat tissue surrounding the colon can sense bacterial signals and trigger precise immune responses,” says Lucas Massier, junior group leader at the Helmholtz Institute for Metabolic, Obesity and Vascular Research (Helmholtz-Institut für Metabolismus-, Adipositas- und Gefäßforschung, HI-MAG), an institute from Helmholtz Munich at the University of Leipzig and the University of Leipzig Medical Center, and corresponding author of the study. "These findings challenge the traditional view of visceral fat as simply energy storage and may help explain why inflammation is particularly elevated in obesity."
“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, PhD at the same department and co-first author of the study.The study 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.
Original Publication
Jalkanen et al., 2026: Cytoarchitectural multi-depot profiling reveals immune-metabolic crosstalk in human colon-associated adipose tissue. Cell Metabolism. DOI: 10.1016/j.cmet.2025.12.008
