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Use gut bacteria to protect yourself against anxiety, depression, obesity and a host of other mental health issues.

You already know that emotional states have gastrointestinal consequences: Stress causes you stomach pain, you feel butterflies in your stomach before a public speech... - but did you know that gut bacteria imbalances can also damage your mental health?

100 trillion bacteria call your gut home; you're carrying roughly 5 pounds of bacteria, viruses and other eukaryotes right now!1 These microbes play essential roles in our body. Keep a good balance of beneficial gut bacteria and you protect health and well-being. Let bacteria slide out of balance and you put your physical and mental health at risk.

Read on to learn more about...

  • The roles bacteria play in your gut
  • Research that supports gut bacteria’s influence on anxiety, depression and weight management
  • Diseases and conditions associated with gut bacteria imbalances
  • How to promote healthy gut bacteria levels

What Gut Bacteria Do

Your gut (your digestive tract) is essentially a long tube that begins at the back of your mouth and continues to your stomach, small intestines, and to the colon and anus.

  • Your gut is the only organ that has its own nervous system (with over 100 million neurons residing within the walls of the organ).
  • You start out as a newborn with a sterile gut. By age 2 to 4 you have 100 trillion bacteria in your gut. Everyone has a unique mix of different bacterial populations. This mix is influenced by where you live, what you eat, your genetics, your experiences as an infant and other environmental factors
  • Gut bacteria play an essential role in the manufacture of neurotransmitters - such as 95% of the brain’s serotonin. (Serotonin is an important messenger in the brain and in the gastrointestinal tract. Significantly, children who lack certain types of gut bacteria in early development will never produce as much serotonin, even in adulthood, as children with more diverse microflora.)2
  • Gut bacteria help with the digestion and metabolism of food. They extract vitamins and maintain the gut wall - and once beneficial bacteria colonize the gut, they repel pathogens that would otherwise establish a foothold. They do this by optimizing pH and out-competing ‘invaders’ for nutrients.
  • Gut bacteria communicate with dendritic cells of the immune system to quicken the response to harmful germs3 4

We are composed of 30 000 human genes and carry roughly 3 million bacterial genes. Given this, is it any wonder that bacteria have such an influence on so many systems of the body, including cognition and emotional regulation?5

Research: Gut Bacteria’s Influence on Anxiety

Transforming Behavior with Bacteria

Using mice, scientists at McMaster University in Ontario demonstrated that altering gut bacterial levels with antibiotics changes behaviors and anxiety levels.6

After antibiotics and gut bacterial disruption, mice that were normally cautious became adventurous and less anxiety-prone. Or, in another experiment, the researchers demonstrated that by injecting normally active mice with bacteria from more passive mice, they transformed the active mice into timid creatures.

The researchers conclude that altering gut microflora with antibiotics or diet may cause emotional or behavioral changes; they suggest research on the use of probiotics as treatments for behavioral disorders.

UCLA Yogurt Study

UCLA researchers say eating probiotic yogurt twice daily for a month changes the brain’s response to threatening stimuli and induces structural changes in the cortex – dampening reactivity within areas of the brain that cause emotional spikes in response to bodily sensations.

Compared to subjects who ate no probiotic yogurt, subjects given a month of twice daily probiotic yogurt:

  • Showed less neural-emotional response to pictures of threatening faces – particularly in areas of the brain that process and integrate bodily sensations into emotional and cognitive reactions.
  • Had increased connections within cognition areas of the prefrontal cortex

So if a twinge in your gut spikes your anxiety, you may want to consider adding a couple of probiotic yogurts a day.7

Chronic Fatigue Anxiety Study

Subjects with chronic fatigue syndrome were given either probiotics supplements or a placebo for 2 months. After 2 months, those given the probiotics had significantly reduced anxiety scores as measured by the Beck Anxiety Inventory.8

Research: Gut Bacteria’s Influence on Depression

Early-Life Bacterial Deficits Create Life-Long Serotonin Deficits

Gut bacteria play an essential role in the production of serotonin and low serotonin levels are associated with an increased depression risk. In an animal model experiment, Irish researchers found that mice lacking certain gut bacteria during infancy never developed normal serotonin levels, even when they were colonized with essential bacteria later in life. A bacterial deficit in early-life caused an irreversible serotonin deficit through adulthood.9

Research: Gut Bacteria’s Role in Weight Management

Not convinced that gut bacteria play an important role in obesity? Then consider this - give a sample of your gut bacteria to scientists at The University of Florida’s Center for Biotechnical Research and they’ll predict your obesity or leanness with 90% accuracy.10

Danish Obesity Study

In a study of obese and non-obese people in Denmark, obese people were found to have less gut bacterial diversity than healthy-weight people - and over the 9 year study period, people with the least bacterial diversity gained the most weight.11

Bacteria Change Leads to Weight Gain

In an animal model study, mice colonized with bacteria from an obese mouse gained weight more quickly than mice colonized with bacteria from a lean mouse.12

How Does Gut Bacteria Change Brain Function?

Researchers don't yet know exactly how gut bacteria influence our moods, but they’re pretty sure that the vagus nerve - a nerve-line which sends information from the gut to the brain - serves as one key pathway of influence.

Vagus Nerve Experiment

  1. Mice fed a lactobacillus spiked diet became more adventurous and suffered less from stress. They also became more responsive to the neurochemical GABA (a chemical which is also targeted by medications like Xanax.)
  2. However, when the scientists severed the vagus nerve, feeding lactobacillus to mice no longer caused any changes to stress, anxiety or GABA systems.13

Gut bacteria may also cause the release of chemical messengers from the gut into the bloodstream, and eventually into the brain.

What Is Gut Dysbiosis?

Dysbiosis - The condition of having an imbalanced microbiome; too much harmful bacteria and not enough beneficial bacteria.14

An imbalance in the gut impairs beneficial bacteria. Since beneficial bacteria play essential roles in digestion, immune system functioning and even mental health, this can lead to serious health conditions, like

  • Obesity and other metabolic disorders
  • Immune disorders
  • Type 2 diabetes
  • Endotoxemia
  • Inflammatory bowel disease (IBS)
  • Aggravated existing liver disease
  • Food allergies
  • Diminished mental health

How to Protect Healthy Gut Bacteria

100 trillion gut bacteria live and work in an average digestive system. They play important roles and when they get imbalanced we get diseases and mental health problems.

Given this, it makes sense to try to protect our microbiome - to encourage a good balance of beneficial bacteria. Here are a few general tips on maintaining good bacterial health:

  • Avoid unnecessary antibiotic use and limit antibiotic use to short courses, whenever possible
  • Encourage beneficial bacteria with a diet high in probiotics and prebiotics
  • Avoid intestinal parasites and if exposed get treated promptly
  • Be cautious with GERD drugs like proton pump inhibitors which drastically reduce stomach pH. This alteration in pH can lead to a dramatic change in gut flora and in some cases, growth of harmful bacteria at the expense of beneficial bacteria more accustomed to normal stomach pH levels.15
  • Avoid excessive stress – animal research shows that long periods of stress lead to substantial declines in certain beneficial bacteria.16
  • Breastfeed infant children
  • Watch out for excessive hygiene and let small children get a little dirty every now and again – studies show that animals reared in sterile environments don’t develop the same healthy gut microflora as animals raised more naturally.17
  • Make healthy eating choices – minimize consumption of high sugar, high fat and processed foods and maximize consumption of fiber-rich vegetables and fruits (see below for more on how diet influences your microbiome).

Dietary Choices for a Healthy Microbiome

People who consume high fiber, plant-based diets tend to have healthier microflora than people who consume a diet that’s higher in fats and simple carbohydrates (a junk-food diet!)

To encourage a healthy bacterial balance:

  • Avoid a high fat diet – a high fat diet leads to the decrease or elimination of Bifidobacteria spp, a bacterium which plays an essential role in the protection of the gut barrier.
  • Avoid a high sugar diet – too much refined sugar leads to excess bile production and creates a welcoming environment for the opportunistic pathogens C. difficile and C. perfringens (C. difficile is a super-bug that can cause symptoms ranging from mild diarrhea to life-threatening colitis.)18
  • Eat more complex carbohydrates – Complex carbs encourage the growth of beneficial colonies of paratuberculosis and enterobacteriaceae and increase levels of Bifidobacteria spp
  • Consider a high fiber vegetarian diet – high fiber consumption leads to significant fatty acid production (as microbes break-down these fibers.) This lowers pH and decreases pathogenic e-coli bacteria levels.19

Dietary Sources of Probiotics and Prebiotics

If you have gut dysbiosis, restoring a healthy gut microbiome should get you feeling a lot better.

One way to restore gut health is through the consumption of probiotic and prebiotic foods.

These foods are generally very healthy for all people, so with pre and probiotics you have very little to lose and potentially much to gain

Probiotic foods are foods high in beneficial bacteria. Some examples of probiotic foods are:

  • Yogurt (buy one that indicates live active culture on the label)
  • Kefir – a fermented dairy drink
  • Sauerkraut
  • Natto
  • Miso
  • Kimchi
  • Fermented pickles

Prebiotic foods are foods high in the soluble fibers that feed beneficial bacteria – the idea is you can sustain a healthy microbiome by feeding it well. Some examples of prebiotic foods are:

  • Bananas
  • Honey
  • Garlic
  • Onions
  • Leeks
  • Whole grains
  • Artichokes
  • Asparagus
  • Chicory

Are Probiotic Supplements Safe?

As an alternative to pro and prebiotics consumed through food, you can also take a daily dose through supplements.

According to The National Center for Complementary and Alternative Medicine (NCCAM) probiotics are generally well-tolerated and cause few side effects. There is little research evidence to support their long-term safety (or harm). People with pre-occurring serious health conditions may be at greater risk of serious side effects.20

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Page last updated May 26, 2016

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