How does our gut microbiome play a role in our immunity?

Everything we eat and drink passes through the gut along the gastrointestinal (GI) tract. It seems simple enough, but the GI tract, lined with a thin mucous, is embedded with 100’s of trillions of microorganisms that live, grow, and metabolize in what’s considered a complex ecosystem, called the gut microbiome. Your gut microbiome makes up 80% of your immune system and contains 10x more bacterial cells, both beneficial and harmful, than human cells. Everyone’s gut microbiome is different and is as unique as each individual’s fingerprint. Altogether, these microbes may weigh as much as 2–5 pounds, which is roughly the weight of your brain. Together, they function as an extra organ in your body and play a huge role in your health.

Most of us are familiar with the term “Gut-brain axis”. The gut-brain axis is believed to be a bidirectional communication between your gut and the brain, which occurs through multiple pathways that include hormonal, neural, and immune mediators. Your gut bacteria impacts many different key aspects of your health, including how your brain responds to stress (Gut-brain axis), how well your body can digest certain carbohydrates, the health of your immune system, how you store fat, and much, much more. If your gut microbiome is disrupted, it can cause dysbiosis*which leads to chronic illness.

*dysbiosis – an imbalance between healthy and unhealthy microbes present in a person’s natural microflora, especially that of the gut, thought to contribute to a range of conditions of ill health.

This brings us to the question of: What Exactly Does the Gut Microbiome Do Within Our Body?

Maintains Gastrointestinal (GI) Motility
Gut microbes support digesting and moving food through the GI tract by regulating neurotransmission throughout the enteric nervous system of the gut. The microbiome and GI motility have a symbiotic relationship. If the microbiome is altered it can impact motility and issues with motility can also impact the microbiome.

Supports Gut Barrier Integrity
Gut microbes help stimulate the cells that make up the lining of the intestines and regulate the proteins that bind cells in the intestine together. They also boost the development of a type of tissue found exclusively in the gut that assist with immunity called gut-associated lymphoid tissue (GALT).

Competes with Pathogens
Gut microbes compete with pathogens for colonization in the human gut; the healthier the microbiota is, the lower the risk of gut infections.

Produces Short-Chain Fatty Acids (SCFA)
Gut bacteria produce SCFA which have multiple beneficial functions. Two key functions of SCFAs are digestion and anti-inflammatory effects.

Synthesizes Vitamins
Gut bacteria synthesize a selection of important nutrients such as vitamins K2, B12, folate, and thiamine.

Bottom line: The gut microbiome affects the body from birth and throughout life by controlling the digestion of food, immune system, central nervous system and other bodily processes.

What can happen if your Gut Microbiome is Imbalanced?

Because the functions of a healthy gut microbiome are so diverse, any number of symptoms can appear due to dysbiosis*.

Compromised Immune System
Metabolites of beneficial gut bacteria, such as SCFA promote the development of a robust immune system. Gut dysbiosis may impair the immune response, increasing the likelihood of GI infections and respiratory infections.

Your gut bacteria are responsible for “teaching” your immune system how to tolerate proteins in food and environmental allergens such as pollen. When the gut microbiota is disrupted, this teaching process is impaired and the body has a negative reaction to allergens, resulting in food and environmental allergies.

In addition to influencing autoimmune diseases directly linked to the gut, such as Crohn’s disease and ulcerative colitis, we know from emerging research that the gut microbiota also affects the development of non-intestinal autoimmune disorders, including lupus, multiple sclerosis, and type 1 diabetes.

Bone Health
Two of the underlying causes of skeletal issues, such as osteoporosis, are inflammation and nutrient deficiencies. By regulating the body’s inflammatory balance, gut microbes can either promote or inhibit bone loss. A healthy gut microbiome also enhances the absorption of critical bone-building nutrients, including vitamins D and K2, calcium, and magnesium.

Brain Function
The gut microbiome influences the brain and neurobehavior via the gut–brain axis, a network of neurons and signaling molecules linking the enteric nervous system of the gut with the central nervous system. Disruptions of the gut microbiome are implicated in anxiety, depression and neurodegenerative diseases.

Heart Disease
Heart Disease is the leading cause of death worldwide!
Gut dysbiosis causes bacteria to move from the gut into the bloodstream, initiating an inflammatory response that triggers the growth and build-up of arterial plaque (atherosclerosis), which can cause heart attack and stroke.

Type 1 and 2 Diabetes
Gut dysbiosis is highly associated with insulin dysfunction in type 1 diabetes. Studies show that children with type 1 diabetes have lower levels of Lactobacilli and Bifidobacterium (healthy bacterias) compared to children without diabetes. Gut microbes may promote type 1 diabetes by inducing a pro-inflammatory immune response that damages insulin-producing pancreatic beta cells.

The gut microbiome also plays a critical role in type 2 diabetes. Several studies have shown that opportunistic pathogens are increased while microbes that produce a beneficial compound with an anti-inflammatory effect are decreased in type 2 diabetes. The resulting gut dysbiosis allows harmful bacteria into circulation inducing chronic inflammation, an important underlying cause of type 2 diabetes.

Gastrointestinal Health
Not surprisingly, gut microbes play crucial roles in the development and progression of GI disorders, including irritable bowel syndrome (IBS).

In IBS, there is an abundance of pro-inflammatory bacteria such as Enterobacteriaceae and reduced levels of Lactobacillus and Bifidobacterium.

Dysbiosis* may promote obesity by increasing the amount of calories obtained from the diet, by promoting inflammation, increasing appetite, and inflaming the nervous system, leading to overeating.

How do you keep your gut healthy?

Our microbiome is influenced on a daily basis by our food and lifestyle choices, chronic stress, antibiotic use, infections, and toxins. An imbalance in our microbiome, or dysbiosis*, has been implicated in countless chronic health conditions. Making lifestyle and dietary modifications is key in restoring our gut health and function which directly correlates to improving our immune system and minimizing inflammation.

1. Eat a Diverse Range of Foods
As previously stated, there are hundreds of species of bacteria in your intestines. Each species plays a different role in your health and requires different nutrients for growth. Generally speaking, a diverse microbiota is considered to be a healthy one. This is because the more species of bacteria you have, the greater number of health benefits they may be able to contribute to. A diet consisting of different food types can lead to a diverse microbiota!

2. Eat Lots of Vegetables, Legumes, Beans and Fruit
Vegetables, fruit, beans and legumes are the best sources of nutrients for a healthy microbiota. They are high in fiber which can’t be digested by your body, but can be digested by certain bacteria in your gut, which stimulates the growth of healthy gut bacteria. Some high-fiber foods that are good for your gut bacteria include:
● Raspberries
● Artichokes
● Green peas
● Broccoli
● Chickpeas
● Lentils
● Beans (kidney, pinto and white)

Apples, artichokes, blueberries, almonds and pistachios can all increase a beneficial bacteria called Bifidobacteria in humans. Bifidobacteria can help prevent GI inflammation.

3. Eat Fermented Foods
The process of fermenting usually involves bacteria or yeasts converting the sugars in food to organic acids or alcohol. Examples of fermented foods include:
● Yogurt
● Kimchi
● Sauerkraut
● Kefir
● Tempeh

Many of these foods are rich in lactobacilli, a type of bacteria that can benefit your health.

4. Don’t Eat too Many Artificial Sweeteners
Artificial Sweeteners are commonly used as low calorie replacements for sugar. Studies show that they can negatively impact gut bacteria.

5. Eat Prebiotic Foods
Prebiotics are foods that promote the growth of beneficial bacteria in the gut, especially Bifidobacteria.
They are mainly fiber or complex carbs that can’t be digested by human cells. Instead, certain species of bacteria break them down and use them for fuel. Many fruits, vegetables and whole grains contain prebiotics, but they can also be found on their own. A few examples of prebiotic foods include:
● Garlic
● Onions
● Asparagus
● Bananas
● Leeks

6. Eat Whole Grains
Whole grains contain lots of fiber and non-digestible carbs. These carbs are not absorbed in the small intestine and instead make their way to the large intestine. In the large intestine, they are broken down by the microbiota and promote the growth of certain beneficial bacteria such as Bifidobacteria and lactobacilli.

7. Eat a Plant-Based Diet
Diets containing plant-based foods promote the growth of different types of intestinal bacteria than animal-based diets do. A number of studies have shown that vegetarian diets may benefit the gut microbiota. This may be due to their higher fiber contents.

8. Eat Foods Rich in Polyphenols
Polyphenols are plant compounds that have many health benefits, including reductions in blood pressure, inflammation, cholesterol levels and oxidative stress. Polyphenols can’t always be digested by human cells and make their way to the colon, where they can be digested by gut bacteria.
Good sources of polyphenols include:
● Cocoa and dark chocolate
● Red wine
● Grape skins
● Green tea
● Almonds
● Onions
● Blueberries
● Broccoli

To conclude, take care of your gut and it will take care of everything for you. Eat a clean, healthy, plant based diet loaded with nutrients that support your gut health. It is never too late to start eating healthy. If you suffer from dysbiosis and gut problems and need help, I would suggest working with a practitioner who specializes in gut health to manage your specific concerns.

Happy Nourishing Simple Living
Lavanya Kethamukkala, RDN, LDN, CLT