Summary: Researchers have long known that food can influence mood. Some chemicals from food carry messages between the gut and the brain. Gut microbiota (the germs that live in your gut) can change those messages by changing how much of each chemical gets made. In the study, researchers used mice with no gut germs at all. When they added different sets of germs, the mice wanted different foods. That is firm evidence that the gut talks to the brain, and that gut germs play a role in the talk.
People have long trusted their gut feeling to make choices. Science is only now learning how that gut feeling works. People also crave different foods. Some crave eggs, others potato chips. Science has long known that the gut shapes food choices. But how it does that, or how it shapes the brain, has stayed mostly a mystery.
How do the gut and brain talk? How does the gut-brain axis work? These are still hard questions. There are many theories and some weak evidence. But the actual machinery is still mostly unknown. However, a new study by the Department of Biology in the Kenneth P. Dietrich School of Arts and Sciences could firmly establish that food choices are influenced by gut microbes. Before this, despite many theories and guesses, no study gave firm proof that gut germs can change what we eat. So the idea stayed unproven. Until now, only some fruit fly experiments had shown a link between gut germs and food choices. But fruit flies are too different from humans.
In the new study, researchers used mice to test the idea. Mice are mammals, and they are quite close to humans in many ways. The researchers used 30 mice with no gut microbes. They split the mice into three groups. Each group got a very different set of germs. Each group then wanted very different foods.
The idea that gut germs shape human behavior is not new. So the researchers were not surprised. Still, every idea has to be proven.
The gut and the brain talk all day long. When we eat, food releases many kinds of molecules. These molecules act as signals. They tell the brain what to eat and what to skip. But during digestion, gut germs can cut into this talk. They make their own signal molecules that food does not contain. So gut germs may steer the talk between the gut and the brain.
Take a turkey dinner. It raises tryptophan, so you feel drowsy after eating turkey. In the brain, tryptophan turns into serotonin. Then serotonin turns into melatonin, which makes you sleepy.
That is one example of food talking to the brain through the gut. But gut germs can change how much tryptophan a food releases. That changes the message the brain gets. Some gut bacteria may even make tryptophan.
Of course, tryptophan is just one example. The gut-brain link is far more complex. At least tens of known chemicals carry these messages. They may act in different ways in different mixes. So this experiment is just the start of learning how gut germs may shape human behavior.
Also, there is no reliable way yet to measure which germs live in a person’s gut. So no one can measure their role in food choices and behavior. We are still far from the day we can change food choices and behavior by tuning gut germs.
Still, this study is a significant step in the right direction. It is one of the first steps in learning how gut microbes may shape food choices and behavior.
Frequently asked questions
Can gut bacteria cause food cravings?
The evidence says yes. Researchers started with 30 mice that had no gut microbes. They split them into three groups. Each group got a very different set of germs. Each group then wanted very different foods. Earlier work had only shown this link in fruit flies, which are too unlike humans to settle the question. Mice are mammals and much closer to us.
How do gut bacteria talk to the brain?
Through chemical signals. During digestion, food releases molecules that tell the brain what to eat and what to avoid. Gut microbes join that talk. They make their own signal molecules that food does not contain. They also change how much of a food’s chemicals reach the brain. At least tens of known chemicals carry these gut-brain messages, often in mixes.
Why does turkey make you sleepy, and what do gut bacteria have to do with it?
A turkey dinner raises tryptophan. In the brain, tryptophan becomes serotonin, and serotonin becomes melatonin, which makes you drowsy. Gut bacteria can change how much tryptophan a meal releases, and some bacteria make tryptophan themselves. So two people can eat the same meal and get a different signal, depending on the microbes in their gut.
Can I change my cravings by changing my gut bacteria?
Not in a precise way yet. There is no reliable way yet to measure which germs live in a person’s gut. So no one can tune cravings or behavior by changing them. This mouse study is an early, important step. It shows gut microbes help steer food choices. It opens the way to learning how they shape behavior.
Dr. Gurpreet Singh Padda, MD, MBA, MHP
