Happiness and Our Gut Bacteria – new studies and what we can do

yoghurt in bowl


COULD our gut bacteria truly influence our state of happiness?

It appears so. yogurtResearchers worldwide are now investigating the remarkably real relationship between the bacteria in our gut and how we think and
feel. Gut bacterial make-up has been linked to depression, and probiotics, which change the population of gut bacteria, have been shown to alleviate depression in several small studies.

This is what’s known to date:

Massive MIcroorganisms

Massive numbers of microorganisms are thriving within and on our bodies, forming a symbiotic superorganism in every one of us. All together, this superorganism contains vast numbers of bacteria, estimated at 10 to the 14th power (1014 )— 100,000,000,000,000 bacteria! What’s more, our superorganism contains 100 times more genes than the 21,000 in the human genome—2,100,000 genes!

The largest concentration of microorganism— no fewer than 100 trillion bacteria—is found in our guts, specifically in the large intestine of our GI tracts.

Notably, each of us has a unique concoction of gut bacteria. With some 1,100 different species of microorganisms found to date, our gut microenvironments can be as different as we are. Our guts carry about 540,000 microbial genes, only about 55% of which are widely shared.

These microenvironments became what they are today based both on factors beyond and within our control. Among the big factors are:

how we were born—natural birth (which leads to greater variety of bacterial species) or C-section; how we were weaned—breast feeding (greater bacterial variety) or infant formula; age (young and middle-aged adults have greater bacterial variety than older adults);

antibiotics use (infrequent antibiotic users have greater bacterial variety); diet; and overall psychological well-being, including ongoing depression and anxiety.

Serotonin: Manufactured & Regulated in the Gut

It’s also notable that the mood-modulating chemical serotonin, known to relay messages from one brain area of the brain to another and affect brain cells involved in regulating mood, originates in our intestines: 90% of the serotonin in our bodies is produced by cells in our guts.

Reference: https://www.gutmicrobiotaforhealth.com/s/spore-forming-bacteria-regulate-seratonin-biosynthesis-gut

And new research by Jessica Yano at the California Institute of Technology and colleagues, published in 2015 in Cell, shows that the microbial gut community also helps regulate serotonin synthesis. Indigenous gut bacteria signal to colon cells responsible for GI functions, and then those cells increase serotonin synthesis, in part by intensifying the expression of the TPH1 enzyme, which synthesizes it.

Gut Bacterial Dysfunction Linked to Depression

Early research indicates that people with neuropsychological disorders, including depression and autism spectrum disorder, have different microorganism populations than those without the disorders.

In a small study published in 2014 in Neurogastroenterology and Motility, the official journal of the European Gastrointestinal Motility Society, A. Naseribafrouei of Hedmark University College.

in Norway and colleagues compared the fecal microorganism environment (a proxy for the gut environment) of 37 patients with depressive disorder and 18 non-depressed individuals. They discovered that people with depression had fewer kinds of some bacteria (such as Lachnospiraceae) and significantly more of others (such as Bacteroidales and Alistipes).

Why might this happen? “We have a mutually beneficial relationship with gut microorganisms,” says Linghong Zhou, Department of Psychiatry and Behavioural Neurosciences, McMaster University, Canada. “[Our] intestines provide the bacteria with an environment to grow and the bacterium aids in governing homeostasis. Therefore, it is reasonable to think that the lack of healthy gut microbiota [microorganisms in the gut] may also lead to a deterioration of these relationships and ultimately disease.”

Depression & Elevated Antibody Response

An elevated antibody response may play a role in these homeostasis differences. In a small study published in the Journal of Affective Disorders in 2012, Michael Maes of the Maes Clinics @ Tria, in Bangkok, Thailand and colleagues measured serum concentrations of two antibodies, IgA (Immunoglobulin A, which plays a critical role in protect body surfaces exposed to outside foreign substances) and IgM (which causes other immune system cells to destroy foreign substances) in both depressed and non-depressed volunteers after exposure to molecules on the surface of co-existing GI bacteria often responsible for disease. On average, the 112 depressed patients had significantly higher amounts of both antibodies than 28 non-depressed controls. In addition, those with chronic depression had significantly higher IgM antibody levels, and there was a significant correlation between IgA antibody response and GI symptoms.

But Gut Micro-environments Are Malleable

The good news is, we can take measures to modulate our micro-environments. Studies show that taking probiotics, live microorganisms, can influence both our bacterial composition and activity. And although the cause or effect relationship between changes in gut bacteria population and disease is not always clear, ingesting probiotics does seem to influence brain activity related to emotion regulation and uplift mood.

Probiotics & Brain Stimulation

In a small 2013 study, Kirsten Tillisch of the David Geffen School of Medicine at UCLA and colleagues gave 12 healthy women a fermented milk product with probiotics (Bifidobacterium animalis subsp Lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, Lactococcus lactis subsp Lactis) twice a day for 4 weeks. MRI scans showed the probiotic activated the prefrontal cortex and other brain regions associated with emotion regulation. In contrast, no brain change was seen in the two control groups of women who either ingested non-fermented milk or nothing at all.

“The gut provides the largest physical interface between the environment and self,” Tillisch says. “Unlike the skin, our other contact interface with the world, the gut has a complex nervous system, which interfaces directly with the brain and allows bidirectional information flow…This close interaction suggests that aspects of brain development, function, mood, and cognition may be influenced by our gastrointestinal contents.”

Probiotics & Depression Relief

To date, 5 small intervention studies have shown that taking a probiotic has alleviated depression or reduced reactivity to sadness, at least in some individuals:

  1. In a double-blind, placebo-controlled trial published in 2007 in the European Journal of Clinical Nutrition, D. Benton of the University of Wales and colleagues gave 124 volunteers aged 48 — 79 either a probiotic-containing milk drink (Lactobacillus casei Shirota) or a milk-based placebo of similar color and taste but without live bacteria daily for 3 weeks. Afterwards, the probiotic-drinking participants in the bottom third of the depressed/elated scale at the outset reported being happier, while the placebo group reported no such improvement. For those who had a positive outlook to start, consuming the probiotic had no mood effect.
  1. Noting that “heightened cognitive reactivity to normal, transient changes in sad mood is an established marker of vulnerability to depression and is considered an important target for interventions,” researcher Laura Steenbergen from the Leiden Institute for Brain and Cognition, The Netherlands and colleagues conducted a small, triple-blind, placebo-controlled study, published in 2015 in Brain, Behavior, and Immunity. Twenty healthy, non-depressed participants took a multispecies probiotic (Bifidobacterium bifidum W23, Bifidobacterium lactis W52, Lactobacillus acidophilus W37, Lactobacillus brevis W63, Lactobacillus casei W56, Lactobacillus salivarius W24, Lactococcus lactis) for 4 weeks while 20 other participants received a placebo. Compared to the placebo group, participants consuming the probiotic had significantly reduced cognitive reactivity to sad mood, indicated by fewer ruminations and aggressive thoughts.
  1. In a small 2011 double-blind, placebo-controlled, randomized study published in the British Journal of Nutrition, Michaël Messaoudi of the Département de Neuropsychopharmacologie in France and colleagues gave 55 healthy volunteers either a probiotic mixture (containing Lactobacillus helveticus and B. longum) or a placebo for 30 days. Afterwards, the probiotic group had decreased anxiety, depression, and anger-hostility, as well as reduced levels of the stress hormone cortisol compared to the control group. “These results provide… evidence that gut microflora [bacteria and microscopic algae and fungi] play a role in stress, anxiety, and depression,” the researchers say.
  1. In a small, randomized, double-blind, placebo-controlled trial published in Nutritional Neuroscience in 2015, 70 petrochemical workers in Iran took one of three daily treatments—a probiotic yogurt plus one placebo capsule, a non-probiotic yogurt with a probiotic capsule, or a non-probiotic yogurt with a placebo capsule. After 6 weeks, both the probiotic yogurt and probiotic capsule groups showed significant improvements in depression, anxiety, and stress, whereas no such large-scale improvements occurred in workers who didn’t get the probiotics.
  1. Prebiotics work hand in hand with probiotics: Whereas probiotics may change the composition as well as number of gut bacteria, prebiotics solely influence the growth and activity of gut bacteria. They’re defined as ingredients that resist absorption in the GI tract, are fermented by intestinal microorganisms, and selectively stimulate the growth and/or activity of intestinal bacteria potentially associated with health and well-being.


In a small, randomized, double-blind 2014 study of 45 volunteers age 18−45 published in Psychopharmacology, Kristin Schmidt of the University of Oxford and colleagues found that healthy subjects who consumed a B-GOS prebiotic (Bimuno®-galactooligosaccharides) had significantly lowered salivary cortisol levels upon awakening as well as better attention to positive stimuli than other volunteers who took an FOS (Fructooligosaccharides) prebiotic or a placebo (maltodextrin). Cortisol, a hormone, helps modulate the body’s response to stress.

That said, unlike the other studies mentioned, the volunteers who took B-GOS or FOS did not feel less anxious or stressed at the end of the trial.

Conclusions & Caveats

Should people suffering from depression and anxiety take prebiotics and probiotics for possible relief?

If you decide to do so, you may wish to:

  • Eat probiotic foods such as organic plain yogurt, or fermented non-dairy products such as sauerkraut and kimchee. Note that most of the studies that showed results used a probiotic yogurt as the treatment.


That said, these bacteria-braining findings aren’t yet firm. Most of the intervention studies used very small numbers of subjects and haven’t yet been replicated. What’s considered a normal healthy gut microenvironment hasn’t yet been clearly defined. And researchers still don’t know how the gut-brain axis works, only that it does.

“There is some preliminary evidence that probiotics… can also exert some beneficial effects [on the brain],” says gastroenterologist and researcher Dr. Premysl Bercik of McMaster University in Canada. “But at this moment we cannot give any clear advice. First, the clinical data is not available, and second, we will have to find the proper match between the probiotic and the host microbiota. So that means one probiotic will work in one set of patients but not in the others.”



Joy Weinberg is editor-in-chief of Honest Health News, which marries integrative health with strong science-based research to help people revitalize their lives. Follow on Facebook and Twitter @honesthealthnws

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