‘Gut health’ is becoming an increasingly popular term in both mainstream media and scientific communities. The relationship between the gut and the immune system is an ever-evolving, highly complex field of research. Both consumers and researchers are hungry to learn more about how to create a healthy gut microbiome through their diet and lifestyle choices.
It is important to understand how the immune system works, to then understand how it relates to the gut. Essentially, we have human cells which our body recognises as ‘self,’ and then we have other cells (e.g. bacteria, viruses) that our body recognises as ‘non-self.’ When ‘non-self’ cells enter the body, the immune system recognises these foreign bodies and mounts an ‘attack’. When something like salmonella or corona-virus enters the body, this process of recognising a dangerous foreign body begins.
The gastrointestinal (GI) tract (from mouth to anus) has a total area of 400m2, and the highest exposure to the external environment (1). It is home to the largest number of immune and microbe cells in the body (2), and the two work in harmony together to ensure optimal gut and immune health.
If there are so many microorganisms living in our GI tract why doesn’t our immune system fight these bugs off? Essentially, our immune system has an internal recognition system that is able to distinguish between potentially harmful bacteria and the ‘commensal bacteria’ that are safe and use our body as home (3). Immunoglobulin A (sIgA) is an important antibody that lives in the gut and is known for its first line response against potentially harmful pathogens and toxins (1).
To read more about particular nutrients for the immune system, read our last blog post about nutrition for the immune system. Our diet has the ability to very quickly change the gut environment and microbial species within it (4). When we feed ourselves, we are also feeding the millions of microbes that live in our gut, through processes such as fermentation. Poor dietary choices (i.e. the western diet) modulates the gut and is associated with intestinal inflammation, changes in species of bacteria and a gut environment that is potentially more vulnerable to pathogenic infection (1, 5). There are a number of dietary factors to consider when it comes to the gut, which the table below helps to describe.
| Name | Definition/function | Food |
|---|---|---|
| Prebiotics*(6) | A type of fibre that passes through the gastrointestinal tract largely unabsorbed, where it ‘feeds’ the gut bacteria, conferring health benefits. | Underripe bananas, rolled oats, chickpeas, lentils, savoy cabbage, onion, garlic, leek, barley, cashews, grapefruit, soy beans. |
| Probiotics (7) | Live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. These bacteria feed on fibre/prebiotics. | Fermented foods: yoghurt, kefir, sauerkraut, kombucha, pickled vegetables. |
| Postbiotics (8) | A relatively new term that describes the products/metabolites of bacterial fermentation in the gut that are related to health benefits, i.e. short chain fatty acid production (acetate, butyrate, propionate) as a result of prebiotic fibre fermentation. | Foods containing acetate: kombucha, apple cider vinegar, pickled foods. |
*Note: The term prebiotic is almost synonymous with high FODMAP. Many foods high in prebiotics are also high GOS/fructans. Check the app for serving size.
There is still a lot to learn about the benefits of pre/pro/post-biotics, their functions in the body, and how they behave in both health and disease. When it comes to food choices, eating a well-balanced diet, full of colour and variety is most important, rather than focusing solely on specific nutrients or ‘superfoods’. Following your countries nutritional guidelines (e.g. The Australian Guide to Healthy Eating) translates the scientific evidence to ensure you have all your bases and nutrients covered. Some people following a low FODMAP diet may struggle with certain nutrients, or food groups, and it is important to talk to your dietitian or health professional to avoid nutritional deficiencies.
1. Lazar V, Ditu LM, Pircalabioru GG, Gheorghe I, Curutiu C, Holban AM, et al. Aspects of Gut Microbiota and Immune System Interactions in Infectious Diseases, Immunopathology, and Cancer. Front Immunol. 2018;9:1830.
2. Jama HA, Beale A, Shihata WA, Marques FZ. The effect of diet on hypertensive pathology: is there a link via gut microbiota-driven immunometabolism? Cardiovascular Research. 2019;115(9):1435-47.
3. Nadine C-B, Valérie G-R. The immune system and the gut microbiota: friends or foes? Nature Reviews Immunology. 2010;10(10):735.
4. David LA, Maurice CF, Carmody RN, Gootenberg DB, Button JE, Wolfe BE, et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature. 2014;505(7484):559-63.
5. Zinöcker MK, Lindseth IA. The Western Diet-Microbiome-Host Interaction and Its Role in Metabolic Disease. Nutrients. 2018;10(3):365.
6. Gibson GR, Hutkins R, Sanders ME, Prescott SL, Reimer RA, Salminen SJ, et al. Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nature Reviews Gastroenterology & Hepatology. 2017;14(8):491-502.
7. Hill C, Guarner F, Reid G, Gibson GR, Merenstein DJ, Pot B, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014;11(8):506-14.
8. Aguilar-Toalá JE, Garcia-Varela R, Garcia HS, Mata-Haro V, González-Córdova AF, Vallejo-Cordoba B, et al. Postbiotics: An evolving term within the functional foods field. Trends in Food Science & Technology. 2018;75:105-14.
