Explore the intimate but complex relationship between the gut and brain microbiome in a comprehensive study below.
In this article:
- More Scientists Are Looking Into the Gut Microbiome and the Brain
- Gut Microbiome and Brain Link
- Gut-Brain Axis: How the Microbiome Influences Anxiety and Depression
- Leaky Gut and the Old Friend Hypothesis
- The Effects of Diet and Environment on Gut and Brain Microbiome
Brain Microbiome: How Gut Microbiota Develops — and Challenges — the Human Brain
More Scientists Are Looking Into the Gut Microbiome and the Brain
Over the past few years, more scientists are digging deeper into the brain microbiome: What’s the relationship between gut flora and brain function, including behavior?
This question is all due to the growing number of neurodegenerative diseases. These include Alzheimer’s disease (AD), multiple sclerosis (MS), and Parkinson’s disease.
What is Parkinson’s disease? It is a neurological disease characterized by muscle rigidity and tremor.
More people are also dealing with mental disorders like anxiety and depression.
What do gut microbes have to do with these, though? A 2018 research in the Frontiers in Integrative Neuroscience shared the following:
- How the brain and the gut develop together and interact with each other
- A hypothesis called “old friend”
- Impact of leaky gut on the brain
- Changes in society that influence gut microbiota and, in turn, brain function
Gut Microbiome and Brain Link
The study said the gut and brain microbiome tends to develop together. The axis or vagus nerve that links them both also allows them to influence each other.
The body has millions of microbes. In fact, some scientists already recommend using “we” instead of “I” to describe a human being.
You can find them in the:
- Urinary system
- Respiratory system
- Digestive system, especially the gut
The microbiota in the gastrointestinal tract (GI tract) is the most abundant. These microorganisms also have a commensal relationship with the host:
- The body nurtures these microorganisms by providing food and space.
- The gut bacteria then help in the development and function of the different systems of the body. These include immune response and brain function.
Meanwhile, gut bacteria, like the brain, can evolve over time. Factors such as the environment and diet can affect them.
A person’s first exposure to the gut and brain microbiome can also begin as soon as they are born. The microbes they encounter, though, can vary according to the method of delivery.
The vaginal microbiome can provide Lactobacillus to the child. A Caesarian section can increase Clostridium from the mother’s skin.
The diversity and number of gut bacteria can also change. For example, antibiotics at early childhood can delay gut microbiome development.
By the time a child reaches three years old, they can already have the same gut health as an adult. Note that it’s also the age for significant changes in brain skills such as language.
Some studies also cited how gut microbes help the brain and mind mature using animal models. These learned that germ-free mice developed brain defects and abnormal development.
Gut-Brain Axis: How the Microbiome Influences Anxiety and Depression
The Frontiers study also associated gut dysbiosis with poor brain health. These 4 other research areas corroborate it:
1. Irritable Bowel Syndrome (IBS) and Mood Disorders
Irritable bowel syndrome is a cluster of abdominal or digestive symptoms. These include:
- Stomach cramps
- Bloating and gas
- Changing patterns of bowel movements
- Food intolerance
Another symptom is brain fog or mental confusion. An experiment using magnetic resonance imaging revealed people with IBS also had depression and anxiety.
2. IBD and Brain Dysfunction
Inflammatory bowel diseases may also manifest in the brain. A 2018 study used mouse models to illustrate that.
The researchers used a substance known as dextran sodium sulfate (DDS) in mice. It is to induce ulcerative colitis, which is an inflammation in the colon.
They then analyzed the brain tissue of the animals. They discovered that DDS caused changes in the brain structure within three days.
The alteration depends on the region:
- In the hippocampus, which helps regulate emotions, glial fibrillary acidic protein (GFAP) increased. This protein can mean neurotoxic effects in the brain.
- The brain-derived neurotrophic factors (BDNF) in the amygdala decreased. Both are necessary to reduce anxiety.
- Stress hormones and markers of inflammation also went up.
3. Complicated Balance of Microbiome
A healthy microbiota includes species of bacteria, viruses, and fungi. Diversity, though, isn’t enough.
The number can also matter. Take, akkermansia muciniphila, for example.
A. muciniphila is an intestinal species associated with metabolic health and weight loss. In other words, it can help fight obesity by working as one of the probiotics.
On the downside, an overgrowth could damage the mucosal layer of the small intestines. Research in 2018 revealed its association with Parkinson’s disease.
They also associated reduced anxiety and depression with Lactobacillus rhamnosus.
4. Neuroactive Compounds and the Gut
It’s not only the brain that produces neuroactive compounds, such as serotonin, so does the gut!
The gut microbiome can also create short-chain fatty acids (SCFAs). These are metabolites or by-products of microbes when they ferment dietary fiber.
A study in Nature cited how SCFA is vital in gut and brain microbiome. It works with the brain-gut microbiome axis, mediating their interactions.
Leaky Gut and the Old Friend Hypothesis
The Frontiers study talked about theories about the gut and the brain microbiome:
- Leaky gut theory
- Old friend hypothesis
Leaky Gut Theory
Dr. Microbiome has already talked about leaky gut syndrome a lot. You can learn more about it in this post.
Leaky gut can happen for a variety of reasons. One of the possible causes is gut dysbiosis.
It refers to the changes in the diversity and composition of the microorganisms. You may confirm it with microbiome analysis.
A 2019 research said this imbalance may lead to leaky gut syndrome that may increase the risk of Alzheimer’s disease:
- When the gut barrier becomes semi-permeable, it can trigger systemic inflammation.
- This inflammation can damage the blood-brain barrier, a semi-permeable border that helps protect the brain.
- When other substances enter the brain, it can then result in neurological inflammation. It may cause the buildup of amyloid-beta or proteins that destroy nerve cells.
Scientists are also looking into the leaky gut to help understand multiple sclerosis, an autoimmune condition that damages the protective layer of the nerve cells.
A study revealed that gut microbes protect the central nervous system under attack. It will send immune cells when something destroys the protective layer.
An experiment in PLOS ONE, though, showed the effects of leaky gut. After they induced MS-like symptoms on the mice, they learned that:
- They developed a leaky gut.
- The mice showed inflammation in the intestinal barrier. It developed even before the symptoms of MS.
- The researchers also recorded an increase in inflammatory markers.
- The number of T-cells, which help regulate immune response, also dropped.
Old Friend Hypothesis
Professor Graham Rook introduced the old friend hypothesis in 2003. What’s it about?
Humans and microbiomes evolved together and depend on each other to function well. The body cannot and should not exist without these microbes.
The changes in the composition and diversity could explain these common global problems:
- Autoimmune diseases
- Asthma and allergies
The Effects of Diet and Environment on Gut and Brain Microbiome
Frontiers also explored the role of diet and environment in the microbiome and the brain. It also partly touches on the mentioned theory and hypothesis above.
Some of the essential points include:
- High-carbohydrate diets can disturb the microbiota.
- A high-fat diet can also have the same effect, which is dysbiosis. An example is a ketogenic diet, which is a high-fat but low-carb meal plan.
- Probiotics and prebiotics can improve gut and brain microbiomes.
- The gut microbiome can regulate sensitivity to pain. It could increase after antibiotics and decrease with probiotic supplementation.
- A probiotic treatment such as the Nourish Regimen may help.
- Changes in lifestyle can also disrupt the microbial environment in the gut. Staying indoors can limit contact with harmless organisms in pollution-free water and soil.
The study on the gut and brain microbiome is still new, and we can discover more about it later. For now, research suggests this link is strong.
What do you think about the gut-brain axis? Share your thoughts in the comments section below!