This article, reprinted from Dr. Mercola is very important on the relationship between gut bacteria and the brain:
By Dr. Mercola
While many think of their brain as the organ in charge of their mental health, your gut may actually play a far more significant role.
The big picture many of us understand is one of a microbial world that
we just happen to be living in. Our actions interfere with these
microbes, and they in turn respond having more effects to our individual
health as well as the entire environment.
There is some truth to the old expression, having ‘dirt for brains’.
The microbes in our soil, on our plants, in our stomachs are all a
result of our actions. Antibiotics, herbicides, vaccines, and
pesticides, and the tens of thousands of synthetic chemicals we’ve
created all have impacts and result in reactions from these microbes.
Mounting research indicates that problems in your gut can directly
impact your mental health, leading to issues like anxiety and
The gut-brain connection is well-recognized as a basic tenet of
physiology and medicine, so this isn’t all that surprising, even though
it’s often overlooked. There’s also a wealth of evidence showing
intestinal involvement in a variety of neurological diseases.
With this in mind, it should also be crystal clear that nourishing your
gut flora is extremely important, because in a very real sense you have two brains, one inside your skull and one in your gut, and each needs its own vital nourishment. A recent article1 titled “Are Probiotics the New Prozac?” reviews some of the most recent supporting evidence.
Probiotics Alter Brain Function, Study Finds
The featured proof-of-concept study, conducted by researchers at UCLA,
found that probiotics (beneficial bacteria) actually altered
participants’ brain function. The study2 enlisted 36 women between the ages of 18 and 55 who were divided into three groups:
- The treatment group ate yogurt containing several probiotics
thought to have a beneficial impact on intestinal health, twice a day
for one month
- Another group ate a “sham” product that looked and tasted like the yogurt but contained no probiotics
- Control group ate no product at all
Before and after the four-week study, participants underwent functional
magnetic resonance imaging (fMRI) scans, both while in a state of rest,
and in response to an “emotion-recognition task.”
For the latter, the women were shown a series of pictures of people
with angry or frightened faces, which they had to match to other faces
showing the same emotions.
“This task, designed to measure the engagement of affective and
cognitive brain regions in response to a visual stimulus, was chosen
because previous research in animals had linked changes in gut flora to
changes in affective behaviors,” the researchers explained.
Compared to the controls, the women who consumed probiotic yogurt had
decreased activity in two brain regions that control central processing
of emotion and sensation:
- The insular cortex (insula), which plays a role in functions
typically linked to emotion (including perception, motor control,
self-awareness, cognitive functioning, and interpersonal experience) and
the regulation of your body’s homeostasis, and
- The somatosensory cortex, which plays a role in your body’s ability to interpret a wide variety of sensations
During the resting brain scan, the treatment group also showed greater
connectivity between a region known as the ‘periaqueductal grey’ and
areas of the prefrontal cortex associated with cognition. In contrast,
the control group showed greater connectivity of the periaqueductal grey
to emotion- and sensation-related regions.
The fact that this study showed any improvement at all is remarkable,
considering they used commercial yogurt preparations that are
notoriously unhealthy; loaded with artificial sweeteners, colors,
flavorings, and sugar. Most importantly, the vast majority of commercial
yogurts have clinically insignificant levels of beneficial bacteria.
Clearly, you would be far better off making your own yogurt from raw
milk—especially if you’re seeking to address depression through dietary
Yes, Your Diet Affects Your Mood and Mental Health
“Time and time again, we hear from patients that they never felt
depressed or anxious until they started experiencing problems with their
gut. Our study shows that the gut–brain connection is a two-way
street… ‘When we consider the implications of this work, the old sayings ‘you are what you eat’ and ‘gut feelings’ take on new meaning.’”
The implications are particularly significant in our current era of
rampant depression and emotional “malaise.” And as stated in the
featured article, the drug treatments available today are no better than
they were 50 years ago. Clearly, we need a new approach, and diet is an
obvious place to start.
Previous studies have confirmed that what you eat can alter the
composition of your gut flora. Specifically, eating a high-vegetable,
fiber-based diet produces a profoundly different composition of
microbiota than a more typical Western diet high in carbs and processed
The featured research tells us that the composition of your gut flora
not only affects your physical health, but also has a significant impact
on your brain function and mental state. Previous research has also
shown that certain probiotics can help alleviate anxiety:
- The Journal of Neurogastroenterology and Motility5 reported the probiotic known as Bifidobacterium longum
NCC3001 normalized anxiety-like behavior in mice with infectious
colitis by modulating the vagal pathways within the gut-brain.
- Other research6 found that the probiotic Lactobacillus rhamnosus
had a marked effect on GABA levels—an inhibitory neurotransmitter that
is significantly involved in regulating many physiological and
psychological processes—in certain brain regions and lowered the
stress-induced hormone corticosterone, resulting in reduced anxiety- and
depression-related behavior. It is likely other lactobacillus species
also provide this benefit, but this was the only one that was tested.
It’s important to realize that you have neurons both in your brain and your
gut — including neurons that produce neurotransmitters like serotonin.
In fact, the greatest concentration of serotonin, which is involved in
mood control, depression and aggression, is found in your intestines, not your brain! Perhaps this is one reason why antidepressants, which raise serotonin levels in your brain, are often ineffective in treating depression, whereas proper dietary changes often help…
Your Gut Bacteria Are Vulnerable to Your Diet and Lifestyle
Processed, refined foods in general will destroy healthy microflora and
feed bad bacteria and yeast, so limiting or eliminating these from your
diet should be at the top of your list. Following my recently revised nutrition plan
is a simple way to automatically reduce your intake of sugar from all
sources. Processed foods wreak havoc on your gut in a number of
- First, they are typically loaded with sugar,
and avoiding sugar (particularly fructose) is in my view, based on the
evidence, a critical aspect of preventing and/or treating depression.
Not only will sugar compromise your beneficial gut bacteria by providing
the preferred fuel for pathogenic bacteria, it also contributes to
chronic inflammation throughout your body, including your brain.
- Many contain artificial sweeteners and other
synthetic additives that can wreak havoc with brain health. In fact,
depression and panic attacks are two of the reported side effects of aspartame.
Preliminary findings presented at the 65th annual meeting of the
American Academy of Neurology also report that drinking sweetened
beverages―whether they’re sweetened with sugar or artificial
sweeteners—is associated with an increased risk of depression.7
- Processed foods are also typically loaded with refined grains, which turn into sugar in your body. Wheat
in particular has also been implicated in psychiatric problems, from
depression to schizophrenia, due to Wheat Germ Agglutinin (WGA), which
has neurotoxic activity.
- The majority of processed foods also contain genetically engineered (GE) ingredients
(primarily corn and soy), which have been shown to be particularly
detrimental to beneficial bacteria. There are several mechanisms of harm
at work here. For example:
- Eating genetically engineered Bt corn may turn your intestinal flora into a sort of “living pesticide factory,” essentially manufacturing Bt-toxin from within your digestive system on a continuing basis
- Beneficial gut bacteria are very sensitive to residual
glyphosate (the active ingredient in Roundup). Due to mounting
resistance, GE Roundup Ready crops are being drenched with increasing
amounts of this toxic herbicide. Studies have already confirmed that
glyphosate alters and destroys beneficial gut flora in animals, as
evidenced by the increasing instances of lethal botulism in cattle
- Recent research also reveals that your gut bacteria are a key component of glyphosate’s mechanism of harm, as your gut microbes have the identical pathway used by glyphosate to kill weeds!
Your gut bacteria are also very sensitive to and can be harmed by:
Antibiotics, unless absolutely necessary (and when you do,
make sure to reseed your gut with fermented foods and/or a probiotics
Conventionally-raised meats and other animal products, as CAFO animals are routinely fed low-dose antibiotics, plus genetically engineered grains, which have also been implicated in the destruction of gut flora Chlorinated and/or fluoridated water Antibacterial soap
How to Reseed Your Gut Flora
Considering the fact that an estimated 80 percent of your immune system
is located in your gut, reseeding your gut with healthy bacteria is
important for the prevention of virtually ALL disease, both physical and
mental. The first step is to clean up your diet and lifestyle by
avoiding the items listed above. Then, to actively reseed your gut with
beneficial bacteria, you’ll want to:
- Radically reduce your sugar intake. I’m being
repetitive here, to drive home the point that you can take the best
fermented foods and/or probiotic supplements, but if you fail to reduce
your sugar intake you will sabotage your efforts to rebuild your gut
flora. This would be similar to driving your car with one foot on the
accelerator and one on the brake simultaneously. Simply not a good
strategy at all. When you consume sugar at the level of the typical
American you are virtually guaranteed to have a preponderance of
pathogenic bacteria, yeast and fungi, no matter what supplements you are
- Eat traditionally fermented, unpasteurized foods: Fermented
foods are the best route to optimal digestive health, as long as you
eat the traditionally made, unpasteurized versions. Some of the
beneficial bacteria found in fermented foods are also excellent chelators of heavy metals and pesticides, which will also have a beneficial health effect by reducing your toxic load. Healthy choices include:
- Fermented vegetables
- Lassi (an Indian yoghurt drink, traditionally enjoyed before dinner)
- Fermented milk, such as kefir
- Natto (fermented soy)
Ideally, you want to eat a variety of fermented foods to maximize
the variety of bacteria you’re consuming. Fermented vegetables, which
are one of my new passions, are an excellent way to supply beneficial
bacteria back into our gut. And, unlike some other fermented foods, they
tend to be palatable, if not downright delicious, to most people.
As an added bonus, they can also be a great source of vitamin K2 if you
ferment your own using the proper starter culture. We tested samples of
high-quality fermented organic vegetables made with our specific
starter culture, and a typical serving (about two to three ounces)
contained not only 10 trillion beneficial bacteria, it also had
500 mcg of vitamin K2, which we now know is a vital co-nutrient to both
vitamin D and calcium. Most high-quality probiotics supplements will
only supply you with a fraction of the beneficial bacteria found in such
homemade fermented veggies, so it’s your most economical route to
optimal gut health as well.
- Take a high-quality probiotic supplement.
Although I’m not a major proponent of taking many supplements (as I
believe the majority of your nutrients need to come from food),
probiotics are an exception if you don’t eat fermented foods on a
Nurture Your Gut for Optimal Health and Mental Well-Being
Foods have an immense impact on your body and your brain, and eating whole foods as described in my nutrition plan is the best way to support your mental and physical health.
Mounting research indicates the bacterial colonies residing in your gut may in fact play key roles in the development of brain, behavioral and emotional problems—from depression to ADHD, autism
and more serious mental illness like schizophrenia. Certainly, when you
consider the fact that the gut-brain connection is recognized as a
basic tenet of physiology and medicine, and that there’s no shortage of
evidence of gastrointestinal involvement in a variety of neurological
diseases, it’s easy to see how the balance of gut bacteria can play a
significant role in your psychology and behavior.
With this in mind, it should also be crystal clear that nourishing your
gut flora is extremely important, from cradle to grave, because in a
very real sense you have two brains, one inside your skull and one in your gut, and each needs its own vital nourishment.
Cultured foods like raw milk yogurt and kefir, some cheeses, and
fermented vegetables are good sources of natural, healthy bacteria. So
my strong recommendation would be to make cultured or fermented foods a regular part of your diet; this can be your primary strategy to optimize your body’s good bacteria.
If you do not eat fermented foods on a regular basis, taking a
high-quality probiotic supplement is definitely recommended. A probiotic
supplement can be incredibly useful to help maintain a well-functioning
digestive system when you stray from your healthy diet and consume
excess grains or sugar, or if you have to take antibiotics.