Studies show gut bacteria is connected to depression and dementia – here’s what you NEED to do to prevent it

gut bacteria, gut health, improve gut health
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My brain totally broke in 2010 and I felt like I had developed ADHD, depression, and dementia all at once. By scouring the scientific literature, interviewing and consulting with doctors and researchers, and experimenting with my own body and mind, I finally came to understand that it wasn’t just one thing that had caused my brain and body to break, but the accumulation of many things.

One of my main problems: I had an imbalance of healthy and unhealthy bacteria in my digestive system.

Gut Bacteria Overgrowth: The Health Implications

There are approximately 100 trillion microorganisms and 500 known bacterial species living in our guts. That means there are 10 times more bacteria cells in our bodies than human cells and over 90% of our cells are non-human. Simply put, we are more bacterial than we are human (1).

Gut bacteria affect our nervous, hormonal and immune systems and play a key role in countless bodily functions, including the digestion of food and production of vitamins. So not surprisingly, the makeup of these bacteria in our system can affect how we feel physically and mentally.

What Causes Bad Gut Bacteria Overgrowth

But our modern lifestyle isn’t good for our gut bacteria. Stress, bad diet, and medications can reduce probiotic (good) bacteria and increase bad bacteria in our digestive tract.

gut health, how to heal your gut, gut brain connection, gut bacteria

A lot of people today have out-of-balance and dysregulated gut bacteria. So if we want to regain optimal brain and mental health, it’s critical to restore and support the “good germs” in our gut.

In this post, I’ll show you how to increase your good bacteria and reduce your bad bacteria as I did, so that you’ll improve the health of your brain and experience more mental resilience.

The Gut-Brain Connection

Impressive new research shows that there is a connection between our brain and our digestive tract and that the bacteria in our gut can have a profound influence on our behavior, thoughts, and mood.

There’s evidence that healthy gut bacteria actually produces and regulates the number of neurotransmitters in the brain (such as serotonin, dopamine, and GABA), which can affect mood, pain, and cognition (2-4).

Dr. Stephen Collins, a gastroenterology researcher at McMaster University, has done a lot of research in the field and discovered that unhealthy gut bacteria play a key role in causing abnormal behavior (including anxiety and depression). On the other hand, certain strains of good bacteria can reduce stress hormones and anxious behavior.

Gut Health is More than Just Physical

In one study, Collins took the gut bacteria of anxious mice and transplanted it into calm mice. After the transplant, the calm mice started acting nervously. He has also seen the same results with humans (5 – 12).

Studies by Dr. John Cryan, a neuropharmacologist and microbiome expert at the University College Cork, shows that gut bacteria can alter brain chemistry.  

He found that after eliminating the good bacteria in mice, they act in ways that mimic human anxiety, depression, and autism. And in one of his studies, two strains of bacteria were more effective than an antidepressant at treating anxiety and depression (13 – 19).

Lastly, research has found that mice with autistic-like behavior have much lower levels of a common type of bacteria called “Bacteroides Fragilis” than normal mice. They were stressed, antisocial, and had the same digestive problems often found in autism. But when they were fed “Bacteroides Fragilis”, there was a reversal of their autistic symptoms. They became less anxious, communicated more effectively, and showed less repetitive behavior (20, 21).

This is just the tip of the iceberg. A growing number of scientists and practitioners around the world are researching and speaking out about this, explaining that the gut-brain connection can be hacked to treat psychiatric disorders.

How to Heal Your Gut to Improve Gut Health and Mental Health

So without further ado, here are three ways to nurture your good bacteria and eliminate the bad bacteria in your gut.

By following these steps, you’ll feel stronger both mentally and physically.

1. Consume Probiotics In Food and Supplement Form


Simply increasing the number of beneficial bacteria in your gut is one of the most powerful things you can do for your brain and mental health.

Probiotic supplements add good germs to your digestive system, and providing your body with a diverse array of friendly bacteria can significantly reduce your susceptibility to the negative effects of stress. Researchers have found that mice are less anxious when they are fed probiotics, and numerous studies have shown that humans experience less stress, anxiety, rumination, hostility, depression, and aggression when supplementing with probiotics (22-29).

Researchers are starting to uncover how probiotics work to support the brain. One study showed that probiotics can help you naturally produce more GABA, a relaxing amino acid, and neurotransmitter. Amazingly, this same study showed that probiotics not only help your body produce more GABA, but they enhance the sensitivity of the GABA receptors in your brain, making you more susceptible to calming effects of your natural GABA production (27, 21).

Other species of probiotics have also demonstrated an ability to reduce stress hormones and increase tryptophan, serotonin and omega-3 fatty acids in the brain, all of which play a role in proper mood and cognition (30).

So it’s critical to keep your insides flourishing with a healthy colony of good bacteria.

But do you need to just supplement with probiotics?

Not necessarily.

You can also experiment with incorporating probiotic-rich fermented foods into your diet, including sauerkraut, kimchi, kombucha, natto, and pickled cucumbers. And if you can tolerate dairy, foods like kefir and yogurt (unsweetened) are also high in nourishing bacteria.

By eating probiotic foods, you’re promoting the proliferation of good bacteria in your gut, which will then support your brain. They also tend to have a broad combination of bacteria too – more than what can be found in typical probiotic supplements.

One study suggests that young adults experience less social anxiety if they eat fermented food, and another study shows that yogurt eaters experience positive changes in brain function that cause them to react more calmly to visual stimuli (37, 38).

2. Feed The Good Guys With Prebiotics and Resistant Starch

The existing probiotics in our gut also need to be nourished and supported, and this can be done by eating or supplementing and eating prebiotics.

Prebiotics are substances that humans can’t digest, so they pass through our gastrointestinal tract and promote the growth of many different strains of good bacteria in our lower bowel. They are essentially food for the good bacteria in our intestines.

Dr. Phil Burnet, a neurobiologist at Oxford University, published a paper in 2015 showing that people who ingested probiotics have lower levels of cortisol, a key stress hormone, and focused more on positive feedback and less on negative stimuli. He said the results were very similar to when people take anti-depressants and anti-anxiety medication, but without the side effects.

Other research by Burnet shows that prebiotics supports overall brain health in humans and foster the growth of probiotics in mice, which leads to increased levels of several neurotransmitters that reduced anxiety-like behaviour (42-45).

So if you feed the good bacteria, you will feel healthier physically and mentally. Prebiotic-rich foods include sweet potatoes, carrots, onions, asparagus, and squash. These foods are included in my free grocery shopping guide for optimal brain health and you should be eating them regularly. Resistant starch is another potent way to boost your prebiotic intake, and it’s been shown to help prevent and manage chronic disease (46).

Overall, you should also be eating a wide variety of whole foods, including prebiotics and resistant starch, to support your gut health. Eating a standard Western diet for just one day can dramatically change your gut bacteria in a bad way while eating lots of whole foods increases the diversity of good bacteria (39-41).

3. Avoid Antibiotics (unless absolutely necessary)

Seven years ago, I went to the doctor because my asthma was getting significantly worse. A lot of inflammation and phlegm was building up in my lungs. It felt like I was breathing through a straw all of the time.

The doctor incorrectly assumed I had a bacterial infection (I actually had gluten and dairy allergies), so he gave me a course of antibiotics. And then another course. And then another. They did anything.

Broad-spectrum antibiotics don’t differentiate between good and bad bacteria. These drugs not only kill bad bacteria, but they destroy good bacteria too. By the time I was done all three courses of antibiotics, a lot of the good bacteria in my gut was completely wiped out. And not only did my asthma get worse (and my body less able to handle the gluten and dairy I was eating), but my mental health deteriorated as well.

Moral of the story: Antibiotics can save lives, but they can also destroy your health if they aren’t completely necessary. Yet many conventional doctors hand them out like candy on Halloween.

Studies show that antibiotic use can lead to profound changes and rapid loss of diversity in the composition of the gut bacteria and this can lead to other chronic health complications. American children are typically prescribed one course of antibiotics every year, and excessive and inappropriate use can cause serious long-term consequences without probiotic intervention. For example, antibiotics used to treat acne are associated with the development of inflammatory bowel disease (31-34).

An article published in Nature highlights the negative long-term consequences of antibiotic over-prescription. It points out that antibiotics cause significant and possibly permanent changes in gut bacteria, and infants delivered via caesarean section and/or by a mother given antibiotics during pregnancy significantly will have an insufficient level of good bacteria (35, 36).

I don’t want to suggest that antibiotics are absolutely terrible and we should always avoid them. But they are excessively and inappropriately prescribed and their benefits come at a cost. You should be aware of this so you can make an informed choice. If you do decide to take antibiotics, make sure you take probiotics afterward.


Promoting the growth of beneficial bacteria through positive lifestyle choices can make our brains feel great and function optimally. Too much bad bacteria can make you feel mentally weak, tired and ill, and you may even see changes in your personality. I know I did.  

Bacteria have lived inside humans for hundreds of thousands of years and therefore have lots of experience modifying our brains. They are more precise and subtle than pharmaceuticals, meaning means fewer side effects. As a result, changing the composition of our gut bacteria through lifestyle and dietary interventions is emerging as a very effective and practical way to treat anxiety, depression, autism and other mental health disorders (27, 48, 49).

By taking the above three steps, your gut, body, and brain can become stronger and more resilient over time. 

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