A study recently published in Nature describes a “previously unrecognized” sense that facilitates communication between the gut and the brain.

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Co-senior authors M. Maya Kaelberer, PhD, assistant professor of physiology at the University of Arizona College of Medicine – Tucson, and Diego V. Bohórquez, PhD, associate professor of medicine at Duke University, call it the “neurobiotic sense” – or, more simply, the “gut sense.” They place it alongside the “classic” five senses we learn about as children.

“Senses take the physical world around you and transform that information into something your brain can make sense of. For instance, light gets transferred into an electrical signal that the brain understands,” Kaelberer said. “We discovered that a sensory cell in the gut – the neuropod – rapidly communicates to the brain through a direct synaptic contact. In this case, this sense influences how much we eat.”

Using mouse models, Kaelberer found that neuropod cells are like telephones that have the brain on speed dial. The researchers worked out a step-by-step neurochemical pathway in which the gut communicates directly to the brain to tell it when it has food, helping to regulate appetite.

It turns out that bacteria living in the colon – part of the gut microbiome, or the ecosystem of microbes populating the digestive tract – release protein fragments called flagellin in the presence of food.

“For reasons we don’t quite know, when there’s food around, bacteria will shed flagellin, kind of like a dog sheds dander,” Kaelberer said. “When there isn’t food, they stop shedding.”

When neuropods in the colon sense flagellin, they send signals to the brain to let it know about the feast below. Mice ate more when neuropods were altered to stop this line of communication.

To follow up on the current study, Kaelberer wants to learn how distinct types of foods, such as high-fiber or high-fat diets, might affect the microbiome, shaping the conversations the gut has with the brain.

“Is there a way we can use microbes to, maybe subliminally, have us make better decisions about the food we’re eating?” she said.

Kaelberer believes a better understanding of gut-brain communication may someday lead to strategies for influencing human behavior including not only how much we eat but also behaviors that other studies have linked to the gut microbiome, such as sociability.

“The microbiome influences our behavior, but we don’t quite know the precise mechanisms,” she said. “It’s crazy we haven’t figured this out, because the gut sense is probably our oldest sense, and we know very little about how those signals are being filtered and how that drives our decisions. It has huge implications for how we live our lives on a daily basis, let alone how we can tackle diseases.”

The field of inquiry investigating the gut-brain connection is young, but there are already unproven products like supplements, foods and blends lining the shelves of grocery stores, claiming to populate the gut with beneficial bacteria that address various health problems. The science isn’t there yet, but researchers including Kaelberer are hard at work building an evidence base that may someday help us to wiretap – and influence – conversations between the gut and the brain.

It is work that won’t be completed overnight.

“Figuring out these things takes a long time,” she said. “Whenever my students get frustrated, I always say, ‘The reason this is so hard is because nobody has ever done it before. We’re creating knowledge.’ One aspect of my job that I love so much is that I can help put together this story.”