How is your gut connected to immunity?

How is your gut connected to immunity?

The immune system is made up of different organs, tissues and cells situated throughout the body, each performing invaluable roles to keep us healthy. When you think of the immune system, you are most likely to think of the symptoms that you experience when unwell, such as the tonsils and lymph glands, which can become swollen and tender when fighting off an infection.

You may also be aware that 70-80% of immune system is found in the gut. Therefore, if you are looking to improve your immunity, the gut is a good place to start.

The microbiome and immunity

Your body is inhabited by millions of organisms - such as bacteria, fungi, and viruses - that are known collectively as the microbiome. Your microbiome is found in areas that are exposed to the outside environment, including the skin, nose, mouth and all the way through the gastrointestinal tract (the “gut”).

The microbiome supports our immunity by competing for space with invading microorganisms. You are probably familiar with probiotics, where the key aim is to support “friendly bacteria” in the gut. By supporting our microbiome through lifestyle interventions and supplements, such as probiotics, you encourage a healthier composition of bacteria in the gut, which can outcompete the “bad bacteria.” 

The make-up of the microbiome is impacted by factors such as genetics, age, gender, race, pollutants, antibiotics, stress, and nutrition. An unhealthy microbiome can lead to inflammation, a reduced capacity to overcome invaders, and an increased chance of infection¹.

Epithelial barrier

The cells that line the gut are known as epithelial cells. The gut lining is reinforced by a layer of mucus, which contains immune molecules, such as antibodies.

Antibodies are molecules that are trained by the immune system to recognise antigens (foreign substance, bacteria, or virus) and then signal for other molecules to come and destroy them.

The epithelial lining acts as a physical barrier between the microbiome and your blood stream¹.

What happens to microbiome and intestinal lining as we age?

The microbiome and integrity of the intestinal lining are constantly evolving and are heavily influenced by many factors, such as the food we eat, the environment we live in and different bacteria, viruses, and foreign substances that we encounter each day. As we age, several changes occur that impact the gut and immune system interplay and these changes reduce your immune response.

When you are younger, your body has the capacity to easily replenish and restore damaged intestinal cells. In fact, the intestinal epithelial barrier can renew itself every 3 to 5 days! As we age, this ability is reduced, which contributes to the structural and functional alterations seen as we age². The body becomes less able to restore itself in an environment where the body becomes more prone to damage, due to inflammation caused by a build-up of senescent cells that your bodies are less capable of clearing. 

A compromised barrier means that the microbiome is more vulnerable to contact with substances in the blood stream. You may be familiar with the term “leaky gut,” and this is used to describe gaps in the intestinal barrier cells that allow foreign substances to enter the body. This can further add to inflammatory and even autoimmune conditions, such as inflammatory bowel disease, obesity, diabetes, and colorectal cancer.

As you age, the composition of the microbiome changes, becoming less stable and less diverse and this further impacts your ability to defend against invaders.

What can you do to support the gut as you age?

There are many lifestyle and dietary habits that support gut health and maintain a healthy immune response.

Research shows that people that maintain a unique and diverse microbiome are likely to have better mobility and be able to walk faster than those with a less diverse microbiome³.

Some of the ways you can improve the diversity of your microbiome and the integrity of the gut are:

  • Eating a high fibre diet rich in fruits, vegetables, nuts, seeds, and beans.

The Mediterranean diet is well researched for its health benefits and encourages a healthy microbiome. It is rich in fibre, polyunsaturated fats, antioxidants, and anti-inflammatory foods.

  • Including prebiotic and probiotic foods in your diet.
Prebiotic foods create an environment which helps healthy bacteria to grow and thrive.  Foods include garlic, onions, chickpeas, lentils, apples, and bananas. Healthy bacteria feeds on prebiotics and so it is important to include these foods – or take a prebiotic supplement to encourage a healthier microbiome community.
Probiotic foods introduce healthy bacteria to the gut and include sauerkraut, kimchi, pickles, fermented soy (e.g., miso or tempeh), kombucha and Greek yoghurt.

Diets high in plant proteins, such as tofu, beans, lentils, quinoa, and almonds, are associated with a microbiome that has higher proportions of beneficial probiotics strains, Bifidobacterium, and Lactobacillus⁴

  • Avoiding processed foods, high in sugar, salt, or fat.

These foods encourage opportunistic bacteria to grow and, if left unchecked, can result in an off-balance microbiome.

  • Consider restricting calories.

Calorie restrictive diets, such as intermittent fasting, have been found to support the way we age in several ways. In the context of gut health, this dietary approach can improve microbiome diversity and reduce inflammation. When we are eating, its energy and resources are focused on processing and digesting food. Whilst we are in a fasting state, the gut can focus on repair and regeneration.

  • Regular exercise.

Exercise can encourage a healthy microbiome and intestinal barrier in several ways, such as improved circulation, reduced inflammation and supporting regular bowel motions. Regular exercise also supports a healthier microbiome balance.

  • Include supplements that support your gut and immune health.

Supplements to support your immune health include vitamin C, vitamin D, zinc and senolytics – more information can be found in our Tips for improving immunity blog. 

Prebiotics and probiotics support the health of the microbiome. If you are unable to incorporate these foods into your diet, you could consider taking these in supplement form. You may also consider supplementation if you have a condition that effects your gut health, or for additional support following antibiotic treatment.

Natural glycoprotein isolates are an emerging category of supplements that support immunity in the gut.


Suzy Walsh 

BBA (Hons)., BNat., mNMHNZ

Registered Naturopath & Medical Herbalist


¹ Wiertsema, S. P., Van Bergenhenegouwen, J., Garssen, J., & Knippels, L. M. (2021). The interplay between the gut microbiome and the immune system in the context of infectious diseases throughout life and the role of nutrition in optimizing treatment strategies. Nutrients, 13(3), 886. doi:10.3390/nu13030886

² Walrath, T., Dyamenahalli, K. U., Hulsebus, H. J., McCullough, R. L., Idrovo, J., Boe, D. M., McMahan, R. H., & Kovacs, E. J. (2020). Age‐related changes in intestinal immunity and the microbiome. Journal of Leukocyte Biology, 109(6), 1045-1061. doi: 10.1002/jlb.3ri0620-405rr

³ Wilmanski, T., Diener, C., Rappaport, N., Patwardhan, S., Wiedrick, J., Lapidus, J., Earls, J. C., Zimmer, A., Glusman, G., Robinson, M., Yurkovich, J. T., Kado, D. M., Cauley, J. A., Zmuda, J., Lane, N. E., Magis, A. T., Lovejoy, J. C., Hood, L., Gibbons, S. M., … Price, N. D. (2021). Author correction: Gut microbiome pattern reflects healthy ageing and predicts survival in humans. Nature Metabolism, 3(4), 586-586. doi: 10.1038/s42255-021-00377-9

⁴ Tomova, A., Bukovsky, I., Rembert, E., Yonas, W., Alwarith, J., Barnard, N. D., & Kahleova, H. (2019). The effects of vegetarian and vegan diets on gut microbiota. Frontiers in Nutrition, 6.