Gut instinct: what our intestines tell us about how we think
The billions of bacteria that populate our intestines influence a wide range of processes in our bodies—including our behavior and brain development.
By Alexa Boschini ’10
The notion that bacteria living in our intestines could control our behavior sounds more like the plot of a science fiction movie than real human physiology.
But our digestive tracts are actually home to billions of friendly bacteria collectively called the microbiome, and mounting scientific evidence suggests these bugs have an impact on how we think and the choices we make.
Associate Professor of Biology Jennifer Uno dedicates her research to the mysteries of the microbiome, and how our genes, diet and environment affect the role it plays in our physiology, behavior and brain development. “From a physiology standpoint, your intestinal tract is its own little world,” Uno says. “It has its own little immune system. It has to be able to deal with all the happy, friendly bugs that live in the intestine and find a way to cohabitate with them because they are beneficial, but also be able to mount an appropriate immune response if you happen to be exposed to salmonella or listeria.”
Little scholarship exists on the relationship between exercise and the intestinal microbiome, so Uno is working with Marc Gibson ’18, a biology major and Elon College Fellow, to study that connection. Gibson recruited Elon athletes and non-athletes to participate in the study, and he and Uno are analyzing the types of bacteria that comprise the microbiome in both groups as well as how those bacteria function. Studying student-athletes is beneficial, Uno says, because their schedules are so regimented that it’s easy to verify exactly how often they exercise.
Uno and Gibson also have a clearer picture of both groups’ diets than they would studying a broader population, since most students eat at least a portion of their meals on or around campus. They want to learn how the microbiome changes depending on the food people eat, the types of athletic activities they engage in and how frequently they exercise. “I’m guessing we’re going to find certain bacteria in the exercising population that are associated with more lean individuals,” Uno says. “There is a molecule called short-chain fatty acids that is found to have a lot of positive health benefits in the intestine. I think exercise may promote some of the bacteria that are better at producing those.”
The literature on the impact of diet on the microbiome is more robust. Generally, if you ingest fewer calories than you burn, you’ll lose weight. But the makeup of your microbiome also plays a role in weight gain. A diet that is higher in fat and sugar will populate the intestine with bacteria that will make you metabolize and extract calories differently than a person with a healthier diet. And once those bacteria arrive in the intestine, they can actually influence your dietary habits and preferences.
Uno cites a study that showed transferring the gut bacteria of an obese mouse to a thin mouse makes the thin mouse gain weight. Not only does the thin mouse change physically but its eating behaviors change, with a new preference for fattier foods. “A lean person can eat a bowl of Cheerios and an obese person can eat a bowl of Cheerios, and the lean person will get a certain caloric value from it but the obese person will actually get more calories because of the bugs that have populated their intestine,” Uno says. “The more high-fat, high-carb, high-sugar diet you eat, the more you tend to crave that stuff.” Uno attributes those eating behaviors to the gut-brain axis, or the communication pathway that links intestinal physiology to behavior.
She is currently working with students on two other studies rooted in the connection between the gut and the brain. Uno and Alex Ball ’18, a biochemistry major and Lumen Scholar, are exploring the potential link between autism and the microbiome, and together with Emily Bell ’18, a biology major and Honors Fellow, Uno is researching the microbiome’s possible role in anxiety disorders. “Autistic kids tend to have issues with what they eat,” Uno says. “They’re very selective, and any time you’re selective about what you eat it’s going to impact the microbiome. Is that then exacerbating their behavior? It seems like there is some sort of impact.”
Uno and Ball are using antibiotics to modify the microbiomes of zebrafish, which are translucent at a young age making their nervous systems easily visible for study. After altering the microbiome, Uno and Ball noticed the fish began to swim farther apart from each other, a sign of decreased social interaction. Next, they will examine whether those findings connect to serotonin, a neurotransmitter found in both the brain and the gut that some scientists believe is linked to autism. Uno and Bell are also analyzing zebrafish in their anxiety study. When they modulated the fish’s microbiomes with antibiotics, they noticed a change in the fish’s cortisol (a hormone responsible for stress responses) as well as an uptick in anxious behaviors.
The gut-brain axis is a relatively new field of study, so any findings Uno and her students discover will help other scholars exploring the microbiome’s significance. Uno says there is often a certain stigma surrounding the gut, but in her eyes, it’s the coolest organ around. “Just like we don’t have to think about breathing, we don’t have to think about what our guts do,” she says. “It has all of this interesting stuff contained in one organ. Just when I think I’m done and want to look at something different, something like the gut-brain axis will come along and reinvigorate me.”