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Here are some more articles that I found regarding psychobiotics or the use of probiotics to affect behavior and treat psychiatric disorders.  A probiotic is a microorganism introduced into the body for its beneficial properties. Even though the articles are from 2013, they all give slightly different information about this emerging and exciting new field. Please note that psychotropic means having an effect on how the mind works (and it usually refers to drugs that affect a person's mental state). Remember that this area of research and terminology used is in its infancy. From Medscape (November 2013):

Probiotics a Potential Treatment for Mental Illness

Probiotics, which are live bacteria that help maintain a healthy digestive system, are now often promoted as an important part of dietary supplements and natural food products. "Many of the numerous health-improvement claims have yet to be supported scientifically..."

They note that the term "psychobiotic" was created as recent studies have begun to explore a possible link between probiotics and behavior.  "As a class of probiotic, these bacteria are capable of producing and delivering neuroactive substances such as gamma-aminobutyric acid [GABA] and serotonin, which act on the brain-gut axis," they write.

For this review, the investigators sought to examine studies that assessed whether ingesting these bacteria "in adequate amounts" could potentially lead to an effective treatment for depression and other stress-related disorders. In 1 of the preclinical studies examined, mice that ingested L rhamnosus showed reduced anxiety scores and "altered central expression" on both the GABA type A and type B receptors.

And a study of human patients with chronic fatigue syndrome showed that those who consumed an active strain of L casei 3 times a day had significantly higher improvement scores on anxiety measures than did those who received matching placebo. This provides "further support for the view that a probiotic may have psychotropic effects," write the researchers.

Still, Dr. Dinan called for caution. "What is clear at this point is that, of the large number of putative probiotics, only a small percentage have an impact on behavior and may qualify as psychobiotics," said Dr. Dinan. He added that for now, the field needs to wait for large-scale, placebo-controlled trials to provide definitive evidence of benefit and to detect which probiotics have psychobiotic potential.

Dr. Camille Zenobia wrote this in August 2013. From Real Clear Science:

Can 'Psychobiotic' Bacteria Affect Our Mood?

But what about your brain? Apparently, bacteria influence what’s going on up there, too. Within the last several years, a blossoming field of study called “microbial endocrinology” has provided some provocative insights about the relationship between our GI microbiota and our mood and behavior.

Studies in the field of microbial endocrinology have implicated GI microbes as a factor that can regulate the endocrine system. This could have both good and bad effects since the endocrine system is responsible for the production of hormones and coordinates metabolism, respiration, excretion, reproduction, sensory perception and immune function.

From Nov. 2013 Popular Science:

Forget Prozac, Psychobiotics Are The Future Of Psychiatry

The answer lies in the fact that many psychiatric illnesses are immunological in nature through chronic low level inflammation. There is a plethora of evidence showing the link between gut microbiota and inflammation and studies on probiotic strains have revealed their ability to modulate inflammation and bring back a healthy immunological function.  In this regard, by controlling inflammation through probiotic administration, there should be an effect of improved psychiatric disposition.

The authors bring up another reason why psychobiotics are so unique in comparison to most probiotics.  These strains have another incredible ability to modulate the function of the adrenal cortex, which is responsible for controlling anxiety and stress response. Probiotic strains, such as Lactobacillus helveticus and Bifdobacterium longum have shown to reduce levels of stress hormones and maintain a calmer, peaceful state.  There may be a host of other probiotic bacteria with the same ability although testing has been scant at best.

Finally, the last point in support of psychobiotics is the fact that certain strains of bacteria actually produce the chemicals necessary for a happy self.  But as these chemicals cannot find their way into the brain, another route has been found to explain why they work so well.  They stimulate cells in the gut that have the ability to signal the vagus nerve that good chemicals are in the body.  The vagus nerve then submits this information to the brain, which then acts as if the chemicals were there.  

Lately some articles have been mentioning the amazing possibility of new treatments for psychiatric disorders using bacteria as psychobiotics. Think of probiotics (microorganisms that have beneficial effects when consumed) that affect the brain. Researchers promoting the use of this term define a psychobiotic as "a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness". This new emerging field is just in its infancy. Lots of speculation and anecdotal evidence, and a few tantalizing studies.

I think the following article is a good introduction to this research area of the gut and mind/brain interaction, even though it was published in late 2013. Or you could order the newly published scholarly book "Microbial Endocrinology: The Microbiota-Gut-Brain Axis in Health and Disease" (Editors M.Lyte and J.F.Cryan) with a $189. purchase price (!).  From November 2103 NPR:

Gut Bacteria Might Guide The Workings Of Our Minds

Could the microbes that inhabit our guts help explain that old idea of "gut feelings?" There's growing evidence that gut bacteria really might influence our minds

"I'm always by profession a skeptic," says Dr. Emeran Mayer, a professor of medicine and psychiatry at the University of California, Los Angeles. "But I do believe that our gut microbes affect what goes on in our brains.Mayer thinks the bacteria in our digestive systems may help mold brain structure as we're growing up, and possibly influence our moods, behavior and feelings when we're adults. "It opens up a completely new way of looking at brain function and health and disease," he says.

So Mayer is working on just that, doing MRI scans to look at the brains of thousands of volunteers and then comparing brain structure to the types of bacteria in their guts. He thinks he already has the first clues of a connection, from an analysis of about 60 volunteers. Mayer found that the connections between brain regions differed depending on which species of bacteria dominated a person's gut. 

But other researchers have been trying to figure out a possible connection by looking at gut microbes in mice. There they've found changes in both brain chemistry and behavior. One experiment involved replacing the gut bacteria of anxious mice with bacteria from fearless mice"The mice became less anxious, more gregarious," says Stephen Collins of McMaster University in Hamilton, Ontario, who led a team that conducted the researchIt worked the other way around, too — bold mice became timid when they got the microbes of anxious ones. And aggressive mice calmed down when the scientists altered their microbes by changing their diet, feeding them probiotics or dosing them with antibiotics. 

Scientists also have been working on a really obvious question — how the gut microbes could talk to the brainA big nerve known as the vagus nerve, which runs all the way from the brain to the abdomen, was a prime suspect. And when researchers in Ireland cut the vagus nerve in mice, they no longer saw the brain respond to changes in the gut"The vagus nerve is the highway of communication between what's going on in the gut and what's going on in the brain," says John Cryan of the University College Cork in Ireland, who has collaborated with Collins.

Gut microbes may also communicate with the brain in other ways, scientists say, by modulating the immune system or by producing their own versions of neurotransmitters"I'm actually seeing new neurochemicals that have not been described before being produced by certain bacteria," says Mark Lyte of the Texas Tech University Health Sciences Center in Abilene, who studies how microbes affect the endocrine system. "These bacteria are, in effect, mind-altering microorganisms."

This research raises the possibility that scientists could someday create drugs that mimic the signals being sent from the gut to the brain, or just give people the good bacteria — probiotics — to prevent or treat problems involving the brain. Experiments to test whether changing gut microbes in humans could affect the brain are only just beginning. 

One team of researchers in Baltimore is testing a probiotic to see if it can help prevent relapses of mania among patients suffering from bipolar disorder."The idea is that these probiotic treatments may alter what we call the microbiome and then may contribute to an improvement of psychiatric symptoms," says Faith Dickerson, director of psychology at the Sheppard Pratt Health System.

Mayer also has been studying the effects of probiotics on the brain in humans. Along with his colleague Kirsten Tillisch, Mayer gave healthy women yogurt containing a probiotic and then scanned their brains. He found subtle signs that the brain circuits involved in anxiety were less reactive, according to a paper published in the journal Gastroenterology.

But Mayer and others stress that a lot more work will be needed to know whether that probiotic — or any others — really could help people feel less anxious or help solve other problems involving the brain. He says, "We're really in the early stages."