Scientists Discover ‘Sixth Sense’ In The Gut That Controls How Much We Eat
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In A Nutshell
- Scientists have discovered a new “neurobiotic sense” in the colon that lets the body detect bacterial signals and control appetite in real time.
- Specialized gut cells respond to a microbial protein called flagellin, triggering the release of the hormone PYY, which activates the vagus nerve to tell the brain to stop eating.
- Mice lacking this sensing system ate more food and gained more weight, even though they showed no signs of inflammation or immune response.
- This gut–brain circuit works even in germ-free mice, suggesting it may function independently of living bacteria, and could inspire new weight loss treatments.
DURHAM, N.C. — The human body may have a previously unknown sense that rivals sight, smell, taste, touch, and hearing in importance, and it’s located in the gut. Scientists at Duke University have discovered that specialized cells in the colon can detect signals from bacteria and send rapid messages to the brain that control how much we eat.
Published in the journal Nature, researchers reveal what they call the “neurobiotic sense,” a direct communication channel between gut microbes and the nervous system. When this bacterial sensing system breaks down, mice eat more food and gain significantly more weight than normal. The discovery could help explain why disruptions in gut bacteria are linked to obesity and eating disorders in humans.
“To coexist with its resident microorganisms, the host must have a sense to adjust its behavior in response to them,” the researchers write.
How Gut Bacteria Send ‘Stop-Eating’ Signals To The Brain
The key player is flagellin, a protein that forms the whip-like tails bacteria use to swim. Nearly all bacteria share this ancient molecular structure, making it a universal signature that the gut has learned to recognize over millions of years of evolution.
The research team, led by Diego Bohórquez and Maya Kaelberer, focused on specialized gut cells called neuropod cells that line the colon and produce a hormone called PYY. These cells contain TLR5, a protein that acts like a molecular sensor and specifically recognizes flagellin. When researchers examined tissue samples from mice, they found that about 57% of PYY cells in the colon contained TLR5 — the highest concentration anywhere in the intestinal tract.
When flagellin binds to TLR5 on these gut cells, it triggers the release of PYY hormone, which then activates nearby vagus nerve fibers. The vagus nerve acts like a biological highway, carrying signals from the gut directly to the brainstem in seconds. Instead of acting on nerves directly, flagellin stimulates these specialized gut cells, which then reduce feeding through this newly discovered gut-brain circuit.
Mouse Study Shows Gut’s ‘Sixth Sense’ Directly Affects Food Intake
To test whether this system actually controls eating behavior, researchers created mice that lacked TLR5 specifically in their PYY cells while leaving the rest of their bodies unchanged. These modified mice ate larger meals and gained more weight than their normal counterparts, with both male and female mice showing significant increases in food consumption.
Using an automated feeding monitoring system, scientists tracked individual meal patterns with remarkable precision, measuring food intake to the nearest 0.01 grams. The analysis revealed that mice lacking the bacterial sensing system ate larger meals and extended their eating duration, showing the mechanism normally provides a natural “stop eating” signal.
Crucially, this bacterial sensing system operates completely separately from immune responses. When researchers blocked immune signaling pathways, the feeding effects remained unchanged. Similarly, mice with disrupted bacterial sensing showed no signs of inflammation or other immune-related problems typically associated with gut bacteria imbalances.
Perhaps most remarkably, the system works even without any gut bacteria present. When researchers tested germ-free mice (raised in sterile conditions), direct administration of flagellin still reduced food intake. This proves that gut cells can respond to bacterial molecules independently of living bacteria.
Researchers also discovered that flagellin levels naturally increase in the colon after eating, showing the system provides real-time feedback about bacterial activity during digestion to help limit further food intake.
Could Gut Microbes Hold The Secret To Controlling Appetite And Weight?
Current weight loss medications often target brain chemistry or slow digestion, but this research points toward a completely different approach: manipulating the gut’s bacterial sensing system. Future treatments might focus on enhancing the natural communication between gut microbes and appetite control centers in the brain.
Disruptions in gut bacteria composition have been linked to obesity, diabetes, and various metabolic disorders in humans. Understanding how bacterial signals normally regulate appetite could lead to new therapeutic approaches for weight management and eating disorders.
People vary dramatically in their gut bacterial compositions, and these findings show that some individuals might have more or less sensitive bacterial sensing systems. Such differences could help explain why some people naturally regulate their weight while others struggle with overeating.
The gut’s newly discovered sixth sense represents millions of years of evolutionary fine-tuning between hosts and their microbial partners. It’s a balance that keeps bodies healthy and functioning properly.
Disclaimer: This research was conducted in mice. While the findings reveal a novel gut-brain sensory circuit that affects feeding behavior, further studies are needed to determine whether the same mechanism applies to humans.
Paper Summary
Methodology
Researchers used multiple experimental approaches including genetically modified mice that lacked specific bacterial receptors, automated feeding monitoring systems, nerve recordings, calcium imaging of individual cells, and studies with germ-free mice. They measured food intake patterns, weight gain, hormone levels, and cellular responses to bacterial proteins. The main experiments focused on mice with deleted TLR5 receptors specifically in PYY-producing gut cells while keeping other systems intact.
Results
Mice lacking bacterial sensing capabilities in gut cells ate larger meals, gained more weight, and showed disrupted feeding patterns. The researchers identified a direct pathway where bacterial flagellin activates PYY cells in the colon, which then signal the brain via the vagus nerve to reduce food intake. This response occurs within seconds and works independently of immune system activation. Flagellin levels naturally increase after eating, showing the system provides real-time feedback about bacterial activity during digestion.
Limitations
The study used only one type of flagellin from Salmonella bacteria, though flagellin variants exist across different bacterial species. Research was conducted primarily in laboratory mice, requiring validation in humans. The long-term health consequences of disrupting this bacterial sensing system remain unclear. Additionally, the study focused on acute feeding responses rather than long-term weight regulation mechanisms.
Funding and Disclosures
The research was supported by multiple National Institutes of Health grants and other funding sources. Two authors, Diego Bohórquez and Maya Kaelberer, are founders and board directors of the Gastronauts Foundation, a nonprofit organization. Some findings have been filed as a provisional patent application by one of the lead researchers.
Publication Information
“A gut sense for a microbial pattern regulates feeding” was published in Nature journal on July 23, 2025. The research was conducted by a team led by Diego V. Bohórquez and M. Maya Kaelberer at Duke University, with collaborators from multiple institutions including MIT, University of Pennsylvania, and University of Arizona.
