How Your Brain, Gut, and Immune System Work Together To Keep You Healthy

When it comes to building a more resilient immune response, ongoing research continues to uncover powerful links between our gut and immune system.

However, a more comprehensive model has emerged, extending our immune response beyond these two systems.

Known as the gut–immune–brain axis, this dynamic bidirectional communication system involves intricate interactions between the gut, immune responses, and the central nervous system¹.

Our gut microbiota – the vast community of trillions of microorganisms, including bacteria, viruses, fungi, and other tiny life forms, that live inside our digestive tracts – play a crucial role in regulating our physiology.

Research¹ has demonstrated that gut microbes not only influence metabolism, but also modulate host immunity, neurodevelopment and brain function.

Your gut acts like a busy internal control centre. The tiny microbes living there, and the chemicals they produce, don’t just help you digest food; they actually “talk” to your immune system and your brain.

This constant communication helps keep your body balanced, ensuring your natural immune defences remain strong and your nervous system functions properly.

READ MORE | Power up your gut-Immune axis with probiotics for better winter health

The fibre fix

Health issues often stem from a compromised gut microbiome. When your gut lining breaks down, conditions like leaky gut syndrome allow toxins and bad bacteria to slip into your bloodstream.

This doesn’t just cause issues like bloating and a stomach ache; it also sends distress signals to your brain.

In addition to compromised immunity, scientists have found that when this gut-brain connection breaks down, it is linked to serious conditions like depression, anxiety, Alzheimer’s, and Parkinson’s¹.

Interestingly, a recent study has found that a high-fibre diet can help ease certain neurodegenerative conditions like Alzheimer’s².

Published in the journal Cell Reports, the research showed that mice afflicted with the disease experienced less Alzheimer’s-related frailty, including tremors, when fed a high fibre diet.

The team found that feeding the mice anti-inflammatory prebiotic fibre inulin restored balance in their guts.

The researchers explained that inulin makes short-chain fatty acids and other metabolites that concentrate in the gut and can also circulate systemically, improving gut health and reducing chemokine signalling in the brain to modulate the immune response.

The findings bring the gut-immune system to the forefront of neurodegenerative disease pathology, as the gut houses the body’s largest population of immune cells.

READ MORE | Maintain a strong immune system all year for better health and recovery

Fermenting better function

In addition to fibre, including more fermented foods in your diet is another effective way to support healthy gut function and, in turn, enhance immunity.

Kimchi offers a prime example, thanks to a recent study³. This Korean side dish is made from fermented vegetables and has the potential to positively influence the many thousands of important microbes that live in the gut and our immune system.

The study found that kimchi affected the immune system in a targeted way. It increased the activity of immune cells called antigen-presenting cells  (APCs), which ingest pathogens, process them and show pieces of those pathogens on their surface so the body’s helper T cells (which coordinate overall immune response) know to mount a response against those specific pathogens.

Kimchi also increased the activity of certain genes that act like switches, helping these immune cells send clearer signals to T cells.

Most other immune cells stayed the same, meaning kimchi targeted helper T cells rather than activating the entire immune system.

The researchers explain that maintaining this balance is important because the immune system must be able to respond to infections effectively while avoiding excessive inflammation that can damage tissues.

READ MORE | Choose probiotic strains that support your immune system this winter

A two-way street

But is not just the gut that influences our immune response. The bi-directional relationship means the immune system also impacts the gut.

In this regard, scientists at the University of East Anglia in the UK uncovered a hidden link between gut health and the immune system⁴.

While studying the Seychelles warbler, a small songbird found on Cousin Island, researchers found that their immune genes influence which gut microbes thrive.

They say their work sheds light on how animal immune systems and communities of beneficial gut bacteria evolve together, including in humans. The study is published in the journal Microbiome.

Further highlighting the bi-directional relationship, the researchers explained that our immune system may help determine which microbes can live in our gut, while those microbes, in turn, help support and train the individual’s immune system.

References:

1. Park, J.C., Chang, L., Kwon, HK. et al.Beyond the gut: decoding the gut–immune–brain axis in health and disease. Cell Mol Immunol 22, 1287–1312 (2025). https://doi.org/10.1038/s41423-025-01333-3.
2. Makhijani P, Valentino TR, Manwaring-Mueller M, Emani R, Mu WC, Aguirre CG, Tan CR, Rane A, Wilson KA, Kifle A, Chen N, Du H, Wu F, Ng JHY, Ambrose BD, Ashok Kumaar PV, Khan S, Winer S, Wang C, Mortha A, Furman D, Schilling B, Ellerby LM, Rojas OL, Andersen JK, Winer DA. Amyloid-β-driven Alzheimer’s disease reshapes the colonic immune system in mice. Cell Rep. 2025 Sep 23;44(9):116109. doi: 10.1016/j.celrep.2025.116109. Epub 2025 Aug 30. PMID: 40885186; PMCID: PMC12520713.
3. Lee, W., Moon, HR., Choi, H. et al.Single-cell RNA sequencing reveals that kimchi dietary intervention modulates human antigen-presenting and CD4⁺ T cells. npj Sci Food 9, 236 (2025). https://doi.org/10.1038/s41538-025-00593-7.
4. Lee, C.Z., Worsley, S.F., Davies, C.S. et al.Host immunogenetic variation and gut microbiome functionality in a wild vertebrate population. Microbiome 14, 78 (2026). https://doi.org/10.1186/s40168-026-02341-9.