Abdominal fat is far more complex than previously assumed. A new study by researchers from Karolinska Institutet, Steno Diabetes Center Copenhagen, and Helmholtz Munich shows that fat located close to the large intestine has a distinct biological role, containing an unusually high number of inflammatory fat cells and immune cells.
The findings, published in Cell Metabolism, highlight that certain fat depots are specially adapted to communicate with the immune system in the gut region.
Mapping Distinct Fat Depots in the Abdomen
In the study, researchers analysed five different abdominal fat depots in individuals with severe obesity. Their analysis revealed marked biological differences between these fat stores.
Most notably, the epiploic fat tissue along the colon stood out. This depot contained a high concentration of fat cells associated with inflammation, along with a substantial presence of immune cells—unlike other abdominal fat regions.
Bacterial Signals Trigger Immune Activation
To further explore this interaction, the researchers conducted laboratory experiments. These tests showed that bacterial signals can stimulate fat cells to produce proteins that activate immune cells within the surrounding tissue.
As reported by medicalxpress, this finding suggests that fat tissue near the intestine actively participates in immune responses rather than merely storing excess energy.
Fat as an Active Signalling Organ
“Fat tissue doesn’t just store energy—it also acts as an active organ that sends signals affecting the entire body,” said Jiawei Zhong, PhD student at the Department of Medicine, Huddinge, Karolinska Institutet, and co-first author of the study.
He added that a common misconception is that abdominal fat is uniform. “In reality, it consists of several distinct depots with different biological functions,” he explained.
Adaptation to the Gut Microbiome
Taken together, the findings indicate that fat tissue surrounding the colon may have evolved as an adaptation to the gut microbiome. The gut harbours vast numbers of bacteria and other microorganisms that can release inflammatory substances, requiring close interaction with local immune mechanisms.
This specialised fat depot may therefore play a role in monitoring and responding to microbial signals from the intestine.
Clinical Implications Still Under Study
Since the research involved individuals with obesity, the researchers cautioned that it remains unclear whether the same characteristics exist in people of normal weight. Moreover, the direct clinical implications of the findings have yet to be established.
Next Steps: Links to Inflammatory Bowel Disease
Looking ahead, the research team plans to examine the role of colon-associated fat tissue in inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis.
“Now that we know this fat tissue contains both fat cells and immune cells, we want to understand how their interaction influences disease activity,” said Jutta Jalkanen, researcher at the same department and co-first author of the study. “Our goal is to determine whether this tissue helps amplify or sustain inflammation by sending signals that affect immune cells locally.”