Study Shows Anxiety May Be Caused By The Gut

anxiety mood gut health books

Researchers have finally found conclusive proof that the balance of bacteria in your gut may have more to do with your mood than any other contributing factor. Do you struggle with anxiety? Irritability? Depression? How about your friends or children? If yes, then this recently published study done by researchers at McMaster University may provide one of the keys to unlock mental clarity and wellness.

I don’t know about you, but I’ve been waiting for a prominent independent study to draw this connection for a long, long time. My belief in the connection between gut and brain was solidified ages ago by reading Dr. Natasha Campbell McBride’s book, The Gut And Psychology Syndrome. But now it seems that researchers are finally starting to embrace this theory, and with it the obvious ramifications.

You see, if the balance of bacteria in your gut really is affecting your mood, then treating mood disorders may be as simple as helping to proliferate the good kinds of bacteria in your digestive tract. I’ve written about what that sort of gut-improving diet might look like before in my post on Your Gut: Understanding The Keys To Health.

Of course, researchers haven’t yet leaped to that dietary conclusion, but they seem willing to investigate goodies like therapeutic probiotics:

To confirm that bacteria can influence behaviour, the researchers colonized germ-free mice with bacteria taken from mice with a different behavioural pattern. They found that when germ-free mice with a genetic background associated with passive behaviour were colonized with bacteria from mice with higher exploratory behaviour, they became more active and daring. Similarly, normally active mice became more passive after receiving bacteria from mice whose genetic background is associated with passive behaviour.

While previous research has focused on the role bacteria play in brain development early in life, Collins said this latest research indicates that while many factors determine behaviour, the nature and stability of bacteria in the gut appear to influence behaviour and any disruption, from antibiotics or infection, might produce changes in behaviour.

Bercik said that these results lay the foundation for investigating the therapeutic potential of probiotic bacteria and their products in the treatment of behavioural disorders. (source)

Notice also that they said “any disruption… might produce changes in behaviour.”

What can “disrupt” your balance of gut bacteria?

Some of the most common culprits, in no particular order:


I love antibiotics. That statement may shock you, considering that I almost never take them and go out of my way to make sure I don’t eat antibiotic contaminated food. But I’ve got to give antibiotics credit. Even as recently as a century ago, we were terrified by infectious disease. Someone getting an especially virulent strain of a disease was almost certainly going to die. Everyone knew someone who had done just that — caught the gripe, the consumption, the influenza, the scarlet fever, the (fill in the blank) and died. People got cuts on their extremities and ended up losing an arm or a leg because of poor wound care and rampant infections. The world we live in, the world where we let our children climb trees and scrape their knees with little to fear other than potential broken bones, the world where we can get stitches to help deep gouges heal in record time, this world wouldn’t be here today if it weren’t for antibiotics.

All that said, antibiotics work by killing not just the nasty, dangerous bacterias causing infections, but all bacteria — good and bad. This poses a problem for us because our digestive systems are home to more than 1,000 trillion bacteria, and we need them to be in good balance in order to be healthy. A typical course of antibiotics wreaks havoc on these colonies, and if our diet is deficient in any way our guts will repopulate with an imbalance of good bacteria to toxin-producing bacteria and our moods will be adversely affected.

Birth Control Pills

Nearly two-thirds of all women in the U.S. have taken birth control pills on a regular basis. As with antibiotics, oral contraceptives can annihilate the balance of bacteria in the gut.

Processed Foods

Processed junk foods, particularly those high in refined flours and sugars, feed (almost exclusively) the harmful, abnormal bacteria and microbes in our gut. A diet rich in these staples of industrial food will allow these abnormal microbes to thrive, weakening the population of healthy, beneficial bacteria, and leading to an imbalance of gut flora.

Chlorinated Drinking Water

Yes, chlorine keeps your pool spotless. It will do the same thing to your intestine if you ingest it — killing off beneficial as well as abnormal bacteria. And sadly, most of us drinking tap water on a regular basis do ingest chlorinated drinking water.

Yes, there are others.

But I’ve tried to list the most common ones for a single purpose: to demonstrate that not one of us is immune from gut dysbiosis. At some point in our lives, we’ve all regularly consumed something that would shift the balance of bacteria in our digestive tract.

What Can You Do To Restore Gut Balance?

First and foremost, work through the dietary changes listed in this post on gut health. On a real basic level that looks like opting out of industrial foods, consuming more bone broth, and incorporating more cultured, fermented foods in your diet.

Secondly, take a high-quality probiotic. A quality probiotic can be hard to find. Many probiotic supplements are processed in ways that don’t adequately preserve the bacteria strains, instead exposing them to too much oxygen or heat. Or they include strains of bacteria that may not be suited to repopulating the human gut well. You’ll want to find a probiotic that’s actually effective, and that’s simply measured by success. (Where to find high-quality probitioc supplements.)

Beyond these two major steps, I also recommend reading about one of my friend’s journeys to find a natural cure for anxiety and depression.

What Can You Expect When You Re-Introduce Good Bacteria?

When you first start re-introducing good bacteria in your gut through eating more cultured, fermented foods and taking a therapeutic grade probiotic, you’ll probably notice what’s called “die-off” symptoms. Headaches, dizziness, fever, nausea, and other mild cold-like symptoms are all natural parts of experiencing die-off. Basically, as your newly introduced good bacteria start out-competing the bad bacteria already present in your system, the bad bacteria start dying off. When they die off, they produce toxins. Normally, your body is able to eliminate these toxins without you experiencing any symptoms. However, when a radical shift in gut flora takes place, the bad bacteria die off in such large quantities that your body can’t effectively eliminate the toxins created in the die-off. So, you’ll experience the die-off effects, also known as a Herxheimer Reaction.

Don’t worry! The die-off symptoms won’t last long at all, and on the other side of them you’ll be feeling better than ever. And, if this new study is any indication (which I believe it is), you’ll have happier and more balanced moods, too.

(photo by jronaldlee)


  1. Karen says

    Interesting article. I have recently found your site and I am enjoying it very much. Thanks. Great recipes too!

  2. Amethyst Dowdell via Facebook says

    My daughter has been going through a “Nightmare” of constant diarrhea and vomiting for three weeks now. She has been to the ER three times. The last time, the doctor finally put her on antibiotics. He said that it is possible that she may have “Too Much of the Healthy Bacteria” and that the delicate balance is off. He said that they are seeing this more and more. They took a stool sample to culture to determine the cause of her problems, but we have yet to hear the results as they take a while to “grow”…Have you ever heard of having “too much” of the healthy bacteria? She eats WAPF, so she has not been taking any probiotics. I am interested in hearing your findings after reading Dr. Natasha. Have you followed GAPS? Have you used her bio-kult or do you know of anyone using them and being healed of Anxiety, Depression, Autism and STAYING HEALED?

  3. Vinessa Nevala via Facebook says

    Check out a book called “The Second Brain” by Michael Gershon, MD. Did you know that the gut has an almost completely separate nervous system, called the “enteric nervous system”, with very few connections to the central nervous system? In fact, the enteric nervous system has more nerve cells than the entire central nervous system combined, excluding the brain. Gershon also proposes that if we have neuroses in our brain (central system) why not also possibly in our “second brain”, i.e. the gut? It all makes sense when we think of “gut knowing” also.

  4. Amethyst Dowdell via Facebook says

    Food Renegade, do all of the books say basically the same thing? That we need the fermented foods, no grains, etc. ?

  5. says

    Maybe I’m just PMSing, but based on today’s level of irritability, tension, swinging moods and general overabundance of sass — I’m pretty sure I’m well past-due to start taking a good probiotic. Thanks for the reminder. ūüėČ

  6. says

    I’m really tripped out by this research, but glad to see it rolling out. I already intuitively know what’s possible via the gut, having reduced my anxiety by about 80-90% after going Primal. I’m fascinated by the possibilities.

  7. says

    @Amethyst — Pretty much! It’s way over simplifying, but those are the common threads between things like SCD, GAPS, Body Ecology, and other gut-healing diets. Bone broths, fermented foods, no/reduced grains, supplements like fermented cod liver oil, probiotics, etc.

  8. says

    New reader to the blog and glad to find beautiful minds here who love optimum health!

    Amazing observation on fermented foods! The foods we use to “scoff” at as kids is now the forerunner to robust health. Ha! God does have a sense of humor!

    Do you think kefir could be included as a nourishing food to the gut? The sour milk could heal, I think. I am not too sure about water kefir though.

    • KristenM says

      I absolutely think kefir would be a great way to introduce fermented foods and help heal the gut, even water kefir. Supposedly water kefir grains used to ferment coconut water makes one of the most probiotic and beneficial beverages out there (although I’ve personally never made it).

  9. Vinessa Nevala via Facebook says

    I’m currently also reading “The China Study”, I recommend it too. It’s bending my preconceptions a bit, but the science — major studies of large populations over 25-30 years — is incredible. The guy’s a rebel, but solid. It’s excellent.

  10. Vinessa Nevala via Facebook says

    Yes, I wouldn’t mind! I can see the benefit of plant-based foods and perhaps our over-emphasis on animal protein, but the question in my mind then remains soy… And I’m not sure whether he talks about cultured or fermented foods. Still, his point about how many diet claims are anecdotal or even fanciful, rather then supported by testing and study is I think worthwhile. And he does blast the “establishment” and its intrinsic reductionism… Plus he’s saying what so many doctors won’t — that diseases can be reversed by diet! Take that, Big Pharma!!! I’ll flag your post, FR, and read it after the book. I want to discover my own questions first and not go forward with a bias, but thank you!

  11. Vinessa Nevala via Facebook says

    BTW, have you read “The Jungle Effect”? My MD recommended it, which astounded me! I mean, conventional medicine doesn’t know, or frankly care, that much about nutrition, so I was impressed. I like finding MDs who buck the “party line”. It’s like they’re covert operators inside the Machine… With us working on the outside, and them shaking things up on the inside, the Machine might crack! I hope so!

  12. says

    This is very interesting to me. I have anxiety “issues” and would love to try a more healthy way of eating to try to help me with this. I am not schooled in nutrition but I know if I put garbage in, I get garbage out.

  13. says

    Interesting study. I’m curious,though, about which studies have shown that oral contraceptives can decimate intestinal flora. Can you provide a link or a citation? Thanks.

    • Amy says

      Seconded; I keep hearing this and I’d love some science to back it up. Deciding to avoid The Pill is a bit more complicated than deciding to avoid grains, or soy, or sugar ūüėČ

  14. Diana Bieniek via Facebook says

    So true for many people. However, some folks have problems with probiotics and fermented foods so it’s difficult for some to rebalance their flora once it’s been disrupted, even with a good diet.

  15. says

    Thanks. Lots of good info here. I forwarded to some friends.

    I wonder how you can tell the difference between die-off symptoms and something just not being good for you.

  16. says

    Actually, the news release says the OPPOSITE of what you are asserting:
    “the researchers showed that disrupting the normal bacterial content of the gut with antibiotics produced changes in behaviour; the mice became LESS cautious or anxious.”

    Can that be right? Considering they open the article talking about the “1000 trillium bacteria” in the gut, I wonder if they messed that up. Off to find the original article, now…

  17. says

    Ok, further reading suggests that the article means what it says: that mice act less anxious and have more brain derived neurotrophic factor (a natural anti-depressant) after their gut flora have been killed by antibiotics.


    • KristenM says

      I think you’re misreading it. The article says:

      “Working with healthy adult mice, the researchers showed that disrupting the normal bacterial content of the gut with antibiotics produced changes in behaviour; the mice became less cautious or anxious. This change was accompanied by an increase in brain derived neurotrophic factor (BDNF), which has been linked, to depression and anxiety.”

      I read it as they become less cautious, or they become anxious. Not that they become “less anxious.” This reading is particularly favored when combined with the following sentence about the antibiotics producing more of the BDNF, which is linked to depression and anxiety.

      • Lee says

        Looked this up via another source and found that mice become EITHER less cautious or anxious. Amazing what a difference one word can make, eh?

  18. Adrienne says

    This is extremely interesting. I have been considering probiotics for a long time, but have had a difficult time discerning between effective and ineffective — even at health food/supplement stores, I get conflicting information. Any recommendations? (The link to suggestions does not work, at least for me.)

    • KristenM says

      Hi Adrienne,

      Are you giving it a moment to load? It’s going to a particular section on my Resources Page, so it has to load the page first then jump to the sub-section. You can also reach it simply by going to my Resources page, then scrolling down to the section on supplements & superfoods.

      If the page is loading, but you don’t see any listings, then that’s a problem with an ad-blocker or a javascript disabler. You’ll need to disable those first for you to see the links.

  19. Tina says

    A personal anecdote of the truth gut issues affecting anxiety:

    I am a celiac with candida – changes in diet have made me healthy. The candida was a long time coming. Despite white bloodcells in my urine, doctors said I was fine until I ended up in the hospital with a bad kidney infection. The antibiotics pushed me over the yeasty edge.

    I began to have panic attacks. Very very aggresive panic attacks with borderline agoraphobia. After a doctor tried to put me on Xanax I started looking into potenital food factors (which is how I initiated the look into candida).

    Anyway, I cleaned up my diet, not only gluten free, but sugar free. The agoraphobia disapeared. The anxiety lessened. But it was still there. Through trial and error, I realized that it was corn. Every time I ate corn my gut would freak out, my kidneys go into overdrive, and cue panic.

    I had a ten year history of health problems being ignored before celiac and then candida diagnosis. My gut is a wreck, but it’s recovering thanks to probiotics, L-Glutamine to repair the damage, and a paleo diet (grassfed beef only, no vegetarian chicken or eggs – which is hard to find).

    The change in diet changed my life and since cutting out corn in all forms (which also means no vegetable oils, corn starch in cheeses, “natural flavors” and citric acid – basically no packaged goods) has meant no more panic attacks.

  20. Sarah S. says

    I just have to say, thank you. Yes, here comes a story.
    In high school I was very out going and took risks. When I was kicked out of school I went traveling and went to different countries. While on my vacation I started having horrible stomach issues and was suddenly very anxious.upon my return to the states I went to see a doctor because I knew something was very wrong. Mmind you I was 16 when I went to them with this issue. They told me I was just aging and have chronic heart burn. They put me on prilosec and sent me on my way. 2 weeks later I went back to the doctor because the prilosec gave me such pain in my stomach I would curl up and cry. The doctor told me to get over it and that was the end of it. Here I am 22 my stomach issues have gotten worse and worse, my anxiety has increased to the point I cry if someone tries to take me somewhere out of my comfort zone and my idiot doctor still tells me its heartburn. He suggests heartburn meds, antidepressants, and counceling. My boss recomended probiotics for me and explained why. I bought some immediatly and am waiting for them in the mail. This fits perfectly! I was in dirty countries eating questionable foods and drinking dirty water when suddenly I had horrible anxiety and stomach issues and my personality changed dramatically. It has gotten worse and worse and has ruinedc my life. I can’t even begin to explain how happy and excited I am to be getting these meds. I’ll actually be back to my old self. I can’t remember the last time I actually felt well and healthy. This article just verified so much so thank you for posting it.

  21. Kevin B says

    I want to get that book! I’m in hell right now with bad panic attacks and fear! I’m trying to get answers but it’s hard. I’m seeing endocrinologist for blood sugar issues, adrenals. I’m always afraid of dying. It sucks. She told me to find a good probiotic. I also have cf, sleep apnea and brain lesions. A mess I know lol. Any advice would be nice. I keep trying :)

  22. Janet Sheko says

    I got on this website to see whether not probiotics could cause anxiety. I have been on the Garden of life raw probiotics for a week for a stomach virus which is called in short the H virus, there have been a couple times where I have felt very very anxious and was wondering if perhaps it could’ve been from the probiotics because it was shortly after taking the probiotics. But I have also been on along with the probiotics, Oreganol, to add in the cleaning of my digestive system and upping my immune system as. And I also am in menopause, and so was wondering if it could be the menopause and the whole reaction between what menopause brings? Oh, I also after three days of being on the probiotics got a yeast infection but it did not last long, it slowly diminished??? Thanks for helping us who are trying to get healthy the right way!

  23. Diana says

    Hello, your link for probiotics went to a website but not a specific product. What probiotics do you recommend? I just started taking a SBO probiotic and my anxiety actually seems worse recently – die off perhaps?


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