How Improving Gut Health Can Optimize the Immune System

The gut is filled with bacteria, viruses, and fungi living together synergistically. While these microbes enjoy a place to live, we benefit from their influence on our digestive system and ability to extract important food nutrients. The gut microbiota also influences our immune system. Five foods to improve gut health can optimize the immune system.

Boost your immune system from the inside

Our environment, genetics, diet, antibiotics, exercise, and stress influence the composition of the gut microbiota. What we consume either helps or hurts the “good” bacteria. Feeding them essential prebiotics can ensure the helpful bacteria maintain a protective presence in the gut.

The helpful and harmful bacteria continually sense their environment and communicate with each other via chemical signals about which proteins to produce and how often to replicate them. These changes in proteins and bacterial growth, in turn, affect gut motility. As a result, people may notice changes in their microbiota with symptoms such as gas or bloating or the consistency of their stool.

Keeping the helpful bacteria supplied with a steady diet of high-quality foods ensures they prevail in this constant competition for resources. In addition, keeping them healthy keeps us healthy from the inside out.

Immune signals sent from the gut

Given that 70–80 percent of our immune cells are in the gut, any changes in the makeup of the “residents” living in the gut microbiota community also affect our susceptibility to infection and low-grade inflammation.

The interface between the microscopic organisms and our immune system lies at the surface of the intestines — the layer of cells forming the gut mucosa. The gut lining is approximately 400 m² (4000 square feet), the size of a large home. This is a substantial surface area interacting with everything we eat, drink, and breathe every day. So it makes sense that the immune system is always on alert, processing information and sending out necessary protective compounds where they are needed.

Think of the gut microbiota as a massive immune processing and distribution center, exerting a considerable influence on both local and systemic immunity via:

• Helping us to metabolize food fully.
• Promoting intestinal repair.
• Suppressing an over-active inflammatory response.
• Preventing pathogens from sticking to cells.
• Sending T cells out to inflamed tissues to protect against infection.
• Influencing T cell differentiation and function.
• Inducing regulatory B and T cells.

How does all this signaling happen?

The work of the gut microbiota is done at the cellular level through various “handshake arrangements” with immune cells. One example is pattern-recognition receptors (PRRs) which take up station within or between cells. The job of the PRR is to recognize specific microbe-associated molecular patterns (MAMPs) which signal an invasion is underway.

One type of PRR some may be familiar with is the Toll-like receptors (TLRs). These proteins are carried by special immune cells (macrophages and dendritic cells), which regularly patrol the body for invaders. When these PRRs pick up a signal suggesting a pathogen has invaded, they activate the innate immune system.

Gut-brain axis – insights from a scientist:

Dr. Christopher Lowry, Ph.D., senior author of what may be the most comprehensive overview of the gut-brain axis published, suggests that “consumption of a diversity of fresh fruits and vegetables not only provides important vitamins and nutrients but also increases the diversity of our gut microbiome.” In addition, Dr. Lowry notes that plants also have unique microbiomes. “For both plants and humans,” Lowry continues, “a diverse microbial community, in turn, is associated with healthy outcomes and increased stress resilience.”

The benefits of paying attention to gut health have intergenerational implications. “What is most exciting for me,” Amy Ogle, MS, RDN, says, “is that we're now beginning to get a glimpse into the multigenerational reach that a healthy (or compromised) microbiota may have.” Ogle is a reproductive nutritionist, exercise physiologist, and co-author of Before Your Pregnancy: A 90-Day Guide for Couples on How to Prepare for a Healthy Conception.

"The gut hosts the largest population of microorganisms, but other organ systems have microbiomes of their own, <…> Being well nourished and physically active can improve your own metabolic health as well as optimize the function of your reproductive organs, mucous membranes, and secretions. All of these factors play a critical role in conception and implantation, and later the infant's own microbiome and immune system."

Amy Ogle, MS, RDN

Taking steps to support the diversity of our own and an infant's microbiota makes eating for two even more rewarding.

How to improve your gut health

It is easy to think of our intestines as just a tube, stretching from end to end, processing food and extracting calories. Sugary foods and salty snacks are so addicting that mindless eating can disconnect us from what healthy food can do for our bodies.

The truth is, our modern fast-food diet is saturated with less-than-healthy foods which may be making us feel unwell. Simple changes to our daily routines can restore gut health, and being mindful of the friendly creatures down below may make these changes a little more satisfying than just switching to an apple a day.

Probiotic food for building good bacteria

Probiotics are the live microbes that comprise the beneficial gut microbiota. Foods that contain live bacterial cultures include yogurt, kefir, kombucha, and fermented foods such as kimchi or sauerkraut. These foods also contain prebiotic fiber that helps build up good bacteria.

A Cochrane Review of 12 clinical trials including 3,720 individuals found that incorporating probiotics reduced the number of acute respiratory tract infections, shortened the duration of infections, and reduced antibiotic use and days absent from school.

However, simply supplementing with a probiotic may delay the recovery of our naturally diverse microbiome after taking antibiotics. For example, in a study of mice treated with antibiotics, those who received autologous fecal microbiome transplant (aFMT) recovered within days, while those given a probiotic took “markedly” longer.

The takeaway message here is, like most things, fresh is best because it promotes diversity in the microbiome.

Prebiotic food for feeding good bacteria

Prebiotics are non-digestible by our enzymes, but can be broken down by the microbiota. As such, they are important “food” for the probiotics (the “good” bacteria), allowing them to help us fully process food and extract important nutrients.

The major players here are short-chain fatty acids (SCFAs) which enable the microbiota to communicate with our cells, keep inflammation under control, and inhibit the formation of cancer cells. One of the most prebiotic-packed foods is the apple — the tart Granny Smith has the highest concentration.

Other good sources of prebiotics include:

Take antibiotics only when necessary

Antibiotics disturb the diversity of helpful bacteria, creating space for the “bad” bacteria to flourish. These so-called opportunistic pathogens suddenly have less competition for resources and grow quickly, disrupting the delicate balance of the microbiota.

When taking antibiotics, be mindful about eating enough probiotic and prebiotic foods to restore the natural flora.

Other methods to optimize the immune response

Other immune-boosting practices include getting enough sleep, drinking enough water, and exercising every day. However, how does each of these common-sense practices work to stimulate the immune system?

Sleep deprivation changes the body's innate and adaptive immune capacity and sets up a chronic inflammatory state which can lead to infections, cancer, heart disease, and autoimmune conditions. On the other hand, getting enough sleep allows the body to release growth hormone, which is critical for cellular repair when recovering from a tough workout or a recent infection.

Drinking enough water allows the immune cells to migrate around the body as needed, navigating between cells as they hunt down invading pathogens. Water also flushes the cellular debris from destroyed pathogens through the kidneys to be excreted.

Finally, emerging research on athletes shows they have a different microbiome primed for metabolic health and tissue repair. Everyone benefits from movement to improve circulation, which is important for carrying immune patrol cells throughout the body, looking for irregular pre-cancerous cells, infections, and tissues needing repair. As these pathogens or dead tissues are picked up by immune cells, they are drained to the lymphatic system and eventually arrive in the lymph nodes (this causes swelling when sick).

Moving the muscles provides a natural “lymph massage” to push these waste products through the lymphatic system. They eventually get filtered out by the liver and kidneys, then excreted as normal waste.

Start taking care of the alimentary army today

The alimentary army is not an abstract entity — it is real and vital to overall health. Starting today, what five probiotic and prebiotic foods can we incorporate into our diet? The suggestions below are just a start:

• Breakfast blueberries. Yogurt topped with oats, blueberries, and honey.
• Afternoon apple. Green apple with peanut butter or a chia/banana/milk or (almond milk) smoothie.
• Spinach salad. Add onion or garlic, tomatoes, and sourdough rye bread.

How to incorporate more movement, water, and sleep:

• Go for a walk or take the stairs.
• Increase water/tea/kombucha intake by eight ounces a day until reaching three liters.
• Start a bedtime routine 30 minutes earlier.
• Avoid alcohol within two hours of bedtime.

Sometimes we have a hard time paying attention to common-sense strategies to boost health until we struggle to recover from an infection. Reframing being slowed down as instead an opportunity to dial into a new self-care phase can launch a “new you.”

The benefits to the microbiome can be detected within as little as 24 hours. Over time, your palate will change, and you will crave these fresh foods, which provide your gut all the diversity it needs to keep you well and moving.