Your Anxiety Could Be Coming from Your Gut—Might Probiotics Calm You Down?

Monday Nov 25 | BY |
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Anxious? Depressed? You may need probiotics.

That our mental state affects our digestive health is a concept most of us are familiar with. What’s new in science is that the health of our digestive system—specifically, the stomach microbes we’re carrying around with us—could have a big impact on our mental health.

In other words, if you’re feeling anxious and you’re not sure what could be causing it, it’s probably not all in your head—but more likely, all in your stomach.

Animal Study Finds Gut Microbes Affects Mental Health

It was back in 2011 that scientists from the Farncombe Family Digestive Health Research Institute at McMaster University in Ontario, Canada, published the results of an animal study indicating that gut microbes could affect mental health. They noted that previous studies had “suggested” that gut bacteria may communicate with the brain, but it was a fairly new concept, and they needed more proof.

Lead author Stephen Collins and colleagues first gave healthy mice a good dose of antibiotics to disturb their natural gut bacteria. They also gave a group of control mice water only. The results showed the following:

  • Behavioral changes: The mice that were given water showed no changes in behavior, but the mice given the antibiotics started acting less like mice. They were less hesitant to step off a platform and more eager to explore—more fearless overall.
  • Brain changes: Mice given antibiotics had an increased amount of brain protein called “derived neurotrophic factor (BDNF)” than mice given water. Such changes in levels of BDNM have been previously linked to depression and anxiety.

In the next stage of the study, the researchers started swapping the gut bacteria in the mice. Different strains of mice have different personalities—some are aggressive, and some more timid. Researchers found that changing gut bacteria made timid mice aggressive, and aggressive mice more passive.

Conclusion: bacteria in the gut produce chemicals that can access and influence the brain.

Possibilities for the future: therapies that aim to restore normal gut flora, including supplementation with probiotics, may be helpful in correcting behavior and mood changes.

Other Studies

An earlier study by Japanese researchers suggested the microflora in our guts are established early in life, after which it’s difficult to change them. Scientists were able to change the baseline stress characteristics of germ-free mice only until nine weeks of age. After that, no matter what bacterial additions they made to the animals’ guts, they couldn’t properly regulate stress and anxiety levels.

“There are changes that happen early in life that we can’t reverse,” said John Cryan, a neuroscientist at the University of Cork in Ireland.

Nevertheless, though we may be stuck with a basic programming between the gut and the brain that is established while we’re infants, researchers remain hopeful that tweaking those bacteria later in life can create behavioral and psychological changes.

A study led by Cryan and published in 2011 showed that anxious mice who were given the probiotic bacterium Lactobacillus rhamnosus displayed lower levels of anxiety, decreased stress hormones, and even an increase in brain receptors for a neurotransmitter vital to curbing worry, anxiety, and fear.

Veterans with Mental Health Disorders More Likely to Have Gastrointestinal Disorders
In March 2013, another study was published that again, linked mental health issues with microbes in the gastrointestinal system. Researchers examined the health records of over 600,000 Iraq and Afghanistan veterans from October 7, 2001 to December 31, 2010. They then analyzed all these records, looking for connections between gastrointestinal disorders (GIDs) and posttraumatic stress disorder (PTSD). Results showed:

  • The prevalence of GID in newly returning veterans was nearly 20 percent.
  • Veterans with a mental health disorder were at least twice as likely to have a GID as those without mental health disorders.
  • For women, the increased risk of all GIDs was greatest among those with depression.
  • Among men, the increased risk of irritable bowel syndrome (IBS) was greatest among those with PTSD.
  • IBS was the GID most strongly associated with mental health conditions among both genders.

Might Probiotics Help?

As to whether probiotics might help ease anxiety, PTSD, and other mental health issues, the jury is still out. We need a number of new studies on the subject. But already we are seeing some suggested benefit. In one 2013 study by UCLA researchers, for example, healthy women who consumed a drink with four added probiotic strains twice daily for four weeks showed significantly altered brain functioning in an fMRI brain scan. The changes indicating an altering of brain regions that control the processing of emotion and sensation.

“Our findings indicate that some of the contents of yogurt may actually change the way our brain responds to the environment,” said lead author Dr. Kirsten Tillisch. “When we consider the implications of this work, the old sayings ‘you are what you eat’ and ‘gut feelings’ take on new meaning.”

Researchers are coming to the conclusion that not only does the brain send signals to the gut, but the opposite is also true—the gut sends signals to the brain.

“Time and time again,” Tillisch said, “we hear from patients that they never felt depressed or anxious until they started experiencing problems with their gut. Our study shows that the gut-brain connection is a two-way street.”

What do you think of these studies? Please share your thoughts.

* * *

Rachael Rettner, “Gut a feeling? Bacteria in the body may affect mood,” NBC News, May 20, 2011,

“That anxiety may be in your gut, not in your head,” McMaster University Press Release, May 17, 2011,

Nobuyuki Sudo, et al., “Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice,” The Journal of Psysiology, July 2004; 558(1): 263-275,

Javier A. Bravo, “Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve,” Proc Natl Acad Sci USA, September 20, 2011; 108(38):16050-16055,

Carrie Arnold, “Gut feelings: the future of psychiatry may be inside your stomach,” The Verge, August 21, 2013,

Shira Maguen, et al., “Association of mental health problems with gastrointestinal disorders in Iraq and Afghanistan veterans,” Depression and Anxiety, March 14, 2013,

Kirsten Tillisch, et al., “Consumption of Fermented Milk Product with Probiotic Modulates Brain Activity,” Gastroenterology, June 2013; 144(7):1394-1401,

Rachel Champeau, “Changing gut bacteria through diet affects brain function, UCLA study shows,” UCLA Newsroom, May 28, 2013,

Colleen M. Story

Colleen M. Story

Colleen M. Story, a northwest-based writer, editor, and ghostwriter, has been creating non-fiction materials for individuals, corporations, and commercial magazines for over 17 years. She specializes in the health and wellness field, where she writes and ghostwrites books, e-books, blogs, magazine articles, and more.

Colleen is the founder of Writing and Wellness. Her fantasy novel, “Rise of the Sidenah,” was released with Jupiter Gardens Press in September 2015. Her literary novel, “Loreena’s Gift,” is forthcoming in spring 2016 from Dzanc Books. She lives in Idaho.


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