Mitchell L. Gaynor M.D.

Your Genetic Destiny

What’s Bugging You?

Studies show that intestinal bacteria may influence our mood.

Posted Apr 09, 2015

Juan Gaertner/
Source: Juan Gaertner/

According to the National Alliance on Mental Illness, mental illness affects approximately 65 million Americans each year. While stress, genetics, and brain chemistry can cause mental illnesses like depression and anxiety, studies show that gut bacteria sends signals to the brain and can change our mood. So these digestive microbes not only influence what we eat but also how we feel.

Bacteria and Health

Bacterial cell populations in our bodies outpace our own cells. It sounds like a sci-fi movie—a bacterial takeover, right? But that’s far from the truth. While the human body comprises 100 trillion bacterial cells (10 times greater than the number of human cells!), the diverse community of bacteria, which largely reside in the gut, work synergistically with our cells to promote good health. Also, the bacterial genome is 150 times greater than the human genome.1 If the scale of bacteria is tipped in favor of bad microbes (largely determined by our diets), then we experience devastating effects to our health. H. pylori, for example, is known to cause stomach ulcers that can lead to cancer.

Gut microbes affect our health in myriad ways: bolster immunity; reduce anxiety, stress, and depression; and regulate weight. Because of these myriad health benefits, it’s in our best interest to enhance healthy bacterial environments in our bodies. And we can do that easily through our diet. Unfortunately, the calorie-rich, nutrient-poor American diet is largely lacking in healthy bacteria. And bacterial strains determined by the foods we eat can help or harm us.

The gut is connected to our nervous, immune, and endocrine (hormone) systems. So when these bugs release enzymes and signaling molecules, those chemicals communicate with the rest of our body to trigger cravings for specific foods and to change our mood. All bacteria—both the good and bad ones—act this way in our gut. This is why it’s imperative that we eat food that contain bacteria that work with our bodies, not against it.

Diversity is key for a healthy gut. In a study, people whose gut bacteria composed low genetic variability had a higher risk of poor glucose control, inflammation, and high cholesterol; obese people in this group also gained a significant amount of weight.2 In another study, researchers found that obese people who ate a low-calorie diet experienced significant increases in the genetic diversity of their gut bacteria.3

Intestinal Bacteria Influence Mood

When microbes release enzymes or signaling molecules, it has a ripple effect that changes the physiology of our bodies for better or for worse. Research is still in the early stages; the mechanisms, by which bacteria affect other parts of the body, are not entirely clear. But what we do know is that our diets cultivate good or bad bacterial ecosystem in our intestines.  

Diet has a tremendous impact on health. And at the level of our DNA, we now know that foods can turn on or off genes in ways that make us healthy or sick. The science that allows us to determine this is called epigenetics. In my forthcoming book, The Gene Therapy Plan: Taking Control of Your Genetic Destiny with Diet and Lifestyle, which will be published on April 21 by Viking, I discuss the effect foods have on our genes and health and the importance of a healthy gut.

Epigenes are chemical tags that sit above our genes, receive signals from the outside world, and transfer these signals to turn genes on or off. And food is one of those signals. So the foods we eat determine many things about our health, one being the bacterial diversity of our guts. And when it comes to certain bacteria, studies show that particular microbes can dampen or enhance your mood.

Animal studies

  • Researchers found that rodents exhibited less anxiety after they were fed a probiotic diet containing Lactobacillus rhamnosus (JB-1).4 Scientists also found that L. rhamnosus altered GABA, a neurotransmitter linked to mood, via the vagus nerve.
  • Compared to normal mice, those that had the bacteria in their gut removed were found to exhibit higher risk-taking behavior; these gut bacteria-free mice also had higher cortisol (stress hormone) levels and altered levels of a brain chemical called BDNF that is linked to anxiety and depression in humans.5

Human studies

  • In a study of healthy women, researchers instructed the study participants to eat probiotic-containing yogurt. After performing brain scans, the scientists found that the pathways involved in anxiety were less responsive.6
  • Another study showed people were less anxious and depressed when they consumed a probiotic mix containing Lactobacillus helveticus and Bifidobacterium longum.7

Although the available research in controlled trials is limited and only shows that there’s an association between gut bacterial strains and our mood, we do know that when we improve our gut flora we enhance our health. To promote gut health, drink plenty of water daily; consume a lot of fibrous foods; eat unprocessed, natural foods; and add fermented foods like yogurt, kefir, and miso soup to your diet.


  1. Qin J, Li R, Raes J, et al. A human gut microbial gene catalogue established by metagenomic sequencing. Nature. 2010;464(7285):59-65.
  2. Le Chatelier E, Nielsen T, Qin J, et al. Richness of human gut microbiome correlates with metabolic markers. Nature. 2013;500(7464):541-546.
  3. Cotillard A, Kennedy SP, Kong LC, et al. Dietary intervention impact on gut microbial gene richness. Nature. 2013;500(7464):585-588.
  4. Bravo JA, Forsythe P, Chew MV, et al. Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve. Proceedings of the National Academy of Sciences of the United States of America. 2011;108(38):16050-16055.
  5. Neufeld KM, Kang N, Bienenstock J, Foster JA. Reduced anxiety‐like behavior and central neurochemical change in germ‐free mice. Neurogastroenterology & Motility. 2011;23(3):255-e119.
  6. Tillisch K, Labus J, Kilpatrick L, et al. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology. 2013;144(7):1394-1401. e1394.
  7. Messaoudi M, Lalonde R, Violle N, et al. Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. Br J Nutr. 2011;105(5):755-764.