Gut Brain Axis & Microbiome Explained

The gut microbiota plays a person’s physiological development. Recent research shows that gut microbiota affects the central nervous system (CNS) and enteric nervous system (ENS). The linkage between the gastrointestinal tract and the nervous system is made possible by the bidirectional pathways commonly known as the gut-brain axis (GBA).

The gut-brain axis consists of multiple connections that involve the vagus nerve, immune system, endocrine system (hypothalamic-pituitary-adrenal axis), and the autonomous nervous system. Dysbiosis (alteration of gut microbiomes) results in gastrointestinal disorders and a host of other diseases affecting other distal organs. Dysbiosis interferes with the gastro-immuno-endocrine-neuro communication pathways leading to central nervous disorders such as autism, depression, and anxiety in patients.

This piece explores the relationship between the brain and the gut and suggests improving the gut microbiome.

What is the gut microbiome?

The human body is packed with billions of viruses, bacteria, and fungi, collectively known as the microbiome. The largest concentrations of microbiomes reside in the digestive tract, the skin, and genitals. Gut microbiota refers to the collection of all microorganisms found in the digestive tract.

Although many different microbiomes exist in the human body, researchers mostly focus on bacteria compositions. The gut microbiota comprises thousands of bacteria species, each playing a unique role in the human body. While some bacteria are harmful and may cause gut diseases, most are beneficial bacteria critical to maintaining good gut health.

However, the composition of gut microbiomes varies across different potions of the digestive tract. Most gut microbes lie in a pocket of space within the colon, called the cecum. The colon contains the highest microbial density, more than all other body organs combined. In human beings, the gut flora begins to form at least a year after birth, when the intestinal epithelium and mucosal barriers have fully developed.

The composition of gut microbiomes changes over time and is largely influenced by changes in diet and an individual’s overall health. Researchers estimate that the genes in the gut flora are ten times more than the entire cells in your body. Collectively, the microorganisms living in the digestive tract weigh around four pounds, which is the typical weight of a human brain. Together, these microbiota function like an extra body organ playing a key role in immunity, nutrition, and mental wellbeing.

How are the gut and brain connected?

The gut is home to millions of neurons that connect to your brain via certain nerves in the nervous system. Neurons rely on chemical signals and electrical impulses to relay information between the nervous system and certain brain parts. The vagus nerve is the organ that connects the brain to the digestive tract. The nerve facilitates the passage of signals between the brain and gut.

Studies show that people under stress can send signals to the gut via the vagus nerve leading to gastrointestinal problems. Further studies reveal that people living with irritable bowel syndrome (IBS), a gastrointestinal disorder, had reduced activity of the vagus nerve (vagal tone).

The second way the brain and gut are connected is through neurotransmitters. Neurotransmitters are chemical substances neurons secrete to relay messages to other organs across the synapse. The information exchange between neurons occurs in the synaptic cleft, a tiny gap between synapses.

The brain produces neurotransmitters which are control emotions and feelings. Serotonin is one such neurotransmitter that creates feelings of happiness. Interestingly, cells in the digestive tract produce a significant portion of all neurotransmitters, including serotonin. Gut microbiomes produce gamma-aminobutyric acid (GABA), a neurotransmitter that controls feelings of anxiety and fear.

Probiotics, prebiotics, and the gut-brain axis

Prebiotics are foods or supplements that promote the development of beneficial bacteria in the digestive tract. Prebiotics are rich in fiber and contain complex carbohydrates which are not easily digestible by human cells. However, certain species of bacteria found in the gut can break down these complex carbs. Prebiotics are found in many whole grains, fruits, and most vegetables. They promote the growth of many types of beneficial microbiomes.

Probiotics refer to many types of live bacteria and yeast, which, when consumed, improve gut health. Probiotics are available as supplements but are also present in yogurts and many fermented foods. Doctors and nutritionists sometimes recommend probiotics to patients with digestive tract disorders. While probiotics contain many forms of bacteria, lactobacillus and Bifidobacterium are the most bacteria in many probiotic supplements.

Interestingly, prebiotics and probiotics can affect your cognitive functioning too due to linkage between the gut and brain via the gut-brain axis (GBA). A recent study reveals probiotics can boost mood and cognitive function in patients with mental disorders.

Further studies show probiotics can reduce depression and anxiety in patients with major depressive disorder (MDD) and irritable bowel syndrome (IBS).

What does the gut microbiome benefit?

Gut microbiomes help reduce inflammation.

Gut microbes play an essential role in reducing gastrointestinal inflammation. Dysbiosis, a condition that arises from the alteration of gut microbes, is one of the major causes of intestinal inflammation and irritable bowel syndrome (IBS).

The gut microbiome can improve heart health.

Besides improving gut health and mental wellness, gut microbiomes are also responsible for good heart health. Recent studies reveal that gut microbiomes are essential in forming beneficial HDL cholesterol. Imbalances in the gut microbiome raise the risk of cardiovascular disease.

A healthy gut microbiome lowers the risk of diabetes.

A healthy gut microbiome helps regulate blood sugars, thus lowering the risk of type 1 and type 2 diabetes. Gut microbiome diversity in infants significantly reduces the risk of type 1 diabetes. Breastmilk, though nutritious, also contains sugar. Gut microbiomes help break down and control sugar levels in breastmilk, thus lowering the risk of high blood sugar among infants.

Gut microbiomes improve brain health.

Serotonin, a neurotransmitter that controls feelings of happiness, is produced by both brain cells and gut cells. Researchers believe up to 90 % of the neurotransmitter is produced by gut cells. Serotonin production boosts mood while helping to suppress anxiety and depression. Taking probiotics can improve gut health and thus improve the outcome of people with major depression disorder (MDD).

How to improve gut microbiome

Below are some ways you can improve your gut microbiome:

Eat a well-balanced diet

Eating a balanced diet comprising diverse foods helps establish microbiome diversity, a key indicator of a healthy gut. The more species of helpful bacteria you have in your gut, the more benefits you stand to gain. Unfortunately, most urban diets score lowly in diversity while being overly saturated with fats and processed sugars.

In comparison, rural diets tend to be richer and more diverse. As a result, people who dwell in rural parts of Africa, Asia, and South America are likely to have better gut microbiome diversity than urban dwellers in North America and Europe.

Increasing intake of legumes and leafy vegetables

Fruits and green leafy vegetables pack many nutrients vital in maintaining a healthy gut microbiome. Beans and legumes are rich sources of fiber and are crucial in developing bifidobacterial microbiomes. Bifidobacteria are helpful bacteria that enhance gut health by preventing inflammation and indigestion.

Fiber-rich foods include broccoli, green peas, bananas, lentils, berries, beans, and other whole-grain meals.

Consuming fermented foods

When food undergoes fermentation, bacteria and yeast break down all its sugars. Fermented foods are rich in lactobacilli, a beneficial bacteria. Yogurt, miso, kimchi, cultured milk, and sauerkraut are fermented foods that enhance the composition and function of beneficial gut microbiomes.

What’s more, regular consumption of yogurt and fermented foods reduces the concentration of Enterobacteriaceae, bacteria that cause gut inflammation, and a host of other chronic gut complications. However, consuming only plain and unflavored yogurts is advisable to enjoy gut health benefits. Flavored yogurts contain high amounts of artificial sweeteners, which raise blood sugar levels and favor the growth of Enterobacteriaceae. Ensure you read product labels of all yogurts to understand their ingredient compositions.

Breastfeed your baby for at least six months

A baby’s gut microbiome starts to develop shortly after birth. Much of the gut microbiome develops during the first two years after birth. Bifidobacteria is among the first to develop and helps digest sugars present in breast milk. Breastfeeding an infant for the first six months enhances the development of these beneficial bacteria.

Bottle feeding infants with commercial baby feed formulas alters the gut microbiome resulting in a lower density of bifidobacteria. More importantly, breastfeeding lowers the risk of obesity, allergies, and health complications. These complications usually arise due to alterations in the gut microbiota.

Consider switching to a plant-based diet.

Numerous studies have shown that plant-based diets enhance gut heath due to high fiber content. A 2013 study linked vegetarian diets to reduced levels of harmful bacteria in obese people. What’s more, a plant-based diet is often associated with low cholesterol while lowering the chances of intestinal inflammation.

Consume foods rich in polyphenols

Polyphenols have many health benefits, including reducing gut inflammation, lowering cholesterol, and oxidative stress in the human body. However, human cells are incapable of digesting polyphenols. Instead, the plant compounds eventually find their way to the colon, where gut bacteria break them down and digest them. Popular sources of polyphenols include red wine, cocoa, dark chocolate, onions, and almonds.