Healthy Gut, Healthy Brain… or Is It All in Your Head?

In Brief:

The gut is the digestive pathway that includes everything your food touches from its trek down the esophagus to its dutiful exit out of the body. The gut also happens to be the home of over 10,000 unique species of microorganisms. Before you shudder at the thought, you should know the reputation of bacteria has been unfairly dragged through the mud. The gut microbiota, which consists of all the bacteria colonized in the digestive tract, is responsible for the processes that stabilize your body’s internal environment. Your gut is not the enemy.

To maintain a balance in bacterial colonies, the gut microbiota transforms into a battleground between good bacteria and hostile viruses. Dysbiosis is when the state of the gut microbiota becomes imbalanced, making it harder to fend off diseases. While we know this vulnerability can cause digestive problems, can the microorganisms also influence behavior?

Researchers believe the central nervous system and the enteric nervous system, a ‘second brain’ in the gut area, can communicate with each other through the gut-brain axis. Disruption in the gut microbiota can intensify stress and panic. Just imagine getting that “butterflies in your stomach” feeling whenever there is some turmoil in your gut.

To test the existence of the gut-brain axis, researchers at Kyushu University created two groups of mice; one group had microbiota removed at birth, while the other group had normally developed microbiota. Both groups were exposed to a stressor. The mice without microbiota reacted with exaggerated fear, while the normal mice recovered faster from the stressor. These responses encouraged researchers to further explore the possibility of the gut-brain axis through tests involving microbiota enhanced with probiotics, foods that increase certain types of good bacteria.

The gut microbiota appears to influence behavior as tested with mice.

This information suggests that the key to reducing behavioral disorders is to fill up on probiotics. But before you stock up on yogurts infused with probiotics during your next trip to the grocery store, be aware that not everyone agrees replenishing a gut with good bacteria will keep the brain healthy. Controversy surrounds the existence of the gut-brain axis; opponents of this idea question how microbes can cross the blood brain barrier, a tightly packed wall protecting the brain from outside invaders. If the microbes cannot even leave the gut, contacting the brain seems unlikely. The communication highway between the brain and the gut is paved on unstable ground.

Dr. Donna Krasnewich, a clinical geneticist, remains skeptical of claims of gut-related anxiety alleviation. When I expressed my own misconceptions of the research — not having a shadow of a doubt that the gut-brain axis existed and thinking researchers are on the brink of revolution — Dr. Krasnewich exclaimed that my argument reflects her exact concern with science writing.

She discussed the lack of clinical research, to which I countered with a study that fed 12 women fermented milk product containing probiotics for four weeks and observed change in emotional response. While this study seems to provide evidence that the gut microbiota composition is related to the brain, Dr. Krasnewich believes the science is more complicated.

“The problem is, you don’t know everything else that happened to that person in the last month; that person may have lost a dog; that person may have gotten married; that person may be pregnant; that person may have developed some disease.”

Dr. Krasnewich argues, “Drawing the conclusion that giving them the probiotic changed their brain scans is a pretty big leap if you don’t know all of the variables in between.”

Perhaps my gut reaction was to immediately agree with the gut-brain axis because it would be helpful to think what I eat could affect my brain. However, as Dr. Krasnewich pointed out, science cannot rely on gut feelings and requires all the facts to be laid down on the table before conclusions are drawn. For this reason, scientists will continue research on communication between the brain and gut. If such a link can be found, scientists can take advantage of this knowledge to help people suffering from mental disorders. In the meantime, by maintaining a healthy gut, we can promote overall health, brain included.


Dr. Donna Krasnewich is a clinical geneticist and practicing pediatrician. She got her medical degree from Wayne State University School of Medicine and now works in Kensington, Maryland. Dr. Krasnewich is also part of the National Institutes of Health, where she is responsible for managing research grants involving genetics.

Works Cited

  1. Thursby, Elizabeth, and Nathalie Juge. “Introduction to the human gut microbiota.” Biochemical Journal, 2017, pp. 1823-1836.
  2. Clapp, Megan, et al. “Gut microbiota’s effect on mental health: The gut-brain axis.” Clinics and Practice, vol. 7, no. 987, 2017, pp. 131-136.
  3. Stein, Rob. “Gut Bacteria Might Guide The Workings Of Our Minds.” NPR, 18 Nov. 2013,
  4. Tillisch, Kirsten, et al. “Consumption of Fermented Milk Product With Probiotic Modulates Brain Activity.” Gastroenterology, 2013, pp. 1394-1401.
  5. Hoban, Alan, et al. “Microbial regulation of microRNA expression in the amygdala and prefrontal cortex.” Microbiome, vol. 5, no. 102, 2017.
  6. Cryan, John F., and Timothy G. Dinan. “Mind-altering microorganisms: the impact of the gut microbiota on brain and behavior.” Nature Reviews Neuroscience, vol. 13, 2012, pp. 701-712.
  7. Krasnewich, Donna. Personal interview by the author. 12 Jul. 2018

Image Credits:
Feature Image:

Bacteria by Unknown (Edited). License: CC0 4.0

Story Image:

Mice by Unknown (Edited). License: CC0 1.0

Chief Editor: Akila Saravanan
Creative Team Manager: Lucia Tian
Team Editor:  Sophie Zhang
Team Graphic Designer:  Lucia Tian

This article was written by Shivani Patel. As always, before leaving a response to this article please view our Rules of Conduct. Thanks! -cSw Editorial Staff