Gut Health and Immunity: Why You Keep Getting Sick

It can be very frustrating when you seem to catch every single cold going around. You might eat plenty of fresh fruit, get lots of sleep, and wash your hands often, but you still end up feeling unwell while your friends stay perfectly healthy. The real reason for your constant sniffles might not be a weak body, but a struggling digestive system.

Because most of your body's natural defences live in your gut, taking a microbiome test may help identify microbiome patterns that could be relevant to immune health and overall well-being.

• Why do I seem to get sick more often than other people? You may be missing some of the beneficial gut bacteria that help support and train your immune system to recognise and respond to harmful germs and viruses.

• Where is my immune system actually located? A large part of your immune system, about 70 percent, is located in your gut and intestines, where it interacts closely with your microbes.

• How do I fix a weak immune system naturally? By taking an advanced test, you may get useful information about your gut microbiome and use this to guide food choices that support beneficial bacteria and overall immune health.

Approximately 70% of the immune system is associated with the gut, particularly within a complex network of tissues called the gut-associated lymphoid tissue, or GALT. This system interacts closely with the gut microbiome and plays an important role in immune function, immune training, and everyday defence against infection. 

This means your gut is a key centre for your body’s defence system. The beneficial bacteria inside it help support immune cells in recognising the difference between harmless substances, such as food, and potential threats such as viruses.

If you do not have enough beneficial bacteria, immune balance may be affected. This may influence how well your body responds to common germs and infections.

Secretory IgA (sIgA) is an important antibody found in the lining of the gut. It helps support the body’s first line of defence by binding to microbes and other substances in the digestive tract before they can interact more closely with the body.

Think of sIgA as part of your body’s frontline defence system. When the gut is balanced, it helps support normal immune function in the digestive tract.

• It helps bind to potentially harmful microbes and toxins in the gut so they can be removed from the body.

• It helps support the protective barrier of the gut lining.

• If sIgA levels are low, it may suggest reduced immune support in the gut.

Yes, gut microbiome imbalance may contribute to systemic inflammation by increasing the movement of microbial products into the bloodstream, which can affect immune responses and may be associated with autoimmunity, a condition in which the body attacks its own healthy tissues.

When harmful microbes outnumber the good ones, they can irritate the gut lining. This may contribute to local inflammation and, in some cases, low-grade systemic inflammation. Persistent inflammation can be associated with fatigue, discomfort, and a general feeling of being unwell [1].

If this inflammation persists, altered immune regulation may be linked to conditions affecting the joints, thyroid, or skin. This is why maintaining a healthy gut microbiome may support long-term health.

T-regulatory cells help control immune responses, and certain beneficial gut bacteria, including some Clostridia species, can support their development and function. These cells help limit excessive immune activity and support recovery after infection.

When you catch a cold, your immune system responds to the virus, which can contribute to symptoms such as fever or sore throat. After the virus is cleared, the immune response needs to be reduced.

Certain groups of beneficial bacteria, including some Clostridia, produce chemical signals that can promote T-regulatory cell activity [2]. These cells help regulate the immune response. If these and other beneficial bacteria are reduced, immune regulation may be affected.

Yes. A stool test can provide information about the composition of the gut microbiome. It may show reduced levels of beneficial microbes or an overgrowth of potentially harmful ones, which could be associated with inflammation or altered immune function.

Probiotics may support gut health, but they do not reliably prevent all illness. Testing first may help guide a more targeted approach to understand your gut’s needs.

Changes in gut health may support immune function over time, but improvement varies between individuals. After following a personalised plan, some people may notice benefits within a few months, with fewer colds and viral infections than usual.

“When people come to us exhausted by back-to-back colds or struggling with ongoing immune-related symptoms, the first place we often look is the digestive system. Since a large proportion of the immune system is associated with the gut, gut microbes play an important role in immune function. If you are lacking certain beneficial bacteria, including some Clostridia species, T-regulatory cell function may be affected, which can contribute to immune dysregulation and inflammation. By using an advanced stool test, we can assess aspects of the gut microbiome. This information may help guide targeted nutrition and other interventions to support gut health and immune resilience.”

[1] Belkaid Y, Hand TW. Role of the microbiota in immunity and inflammation. Cell. 2014 Mar 27;157(1):121-41. doi: 10.1016/j.cell.2014.03.011. PMID: 24679531; PMCID: PMC4056765.

[2] Atarashi K, Tanoue T, Shima T, Imaoka A, Kuwahara T, Momose Y, Cheng G, Yamasaki S, Saito T, Ohba Y, Taniguchi T, Takeda K, Hori S, Ivanov II, Umesaki Y, Itoh K, Honda K. Induction of colonic regulatory T cells by indigenous Clostridium species. Science. 2011 Jan 21;331(6015):337-41. doi: 10.1126/science.1198469. Epub 2010 Dec 23. PMID: 21205640; PMCID: PMC3969237.