Intestines and immunity – how does it work?
“Good immunity” is mainly associated with resistance to seasonal colds, but it is definitely more than that. An efficient immune system constantly provides the body with optimal working conditions:
- prevents pathogens from entering the body, forming protective barriers,
- fends off “attacks” by pathogens: pathogenic bacteria, viruses and fungi,
- distinguishes between “threat” and “neutral” cells (if this process is disturbed, autoimmune diseases can occur),
- forms an immune memory, that is, it remembers the antigens which it has been in contact with and, in the event of reinfection, responds more quickly and efficiently,
- removes abnormal and deformed body cells (if this process does not proceed properly, it can lead to e.g., tumorigenesis).
According to estimates, as many as 70-80% of immune cells are located in the gut, and more specifically in the GALT. It is the body’s first line of defence against parasites, viruses and bacteria. The intestines and mucosa are the habitat of the gut microbiome. The interplay between the gut microbiome, intestinal epithelium and intestinal mucosa is crucial to the proper functioning of the entire immune system.
What is obvious and quite clear is the effect that the gut has on the local immune response in the digestive system. If a pathogen enters the body through the digestive route (e.g. a bacterium with stale food), a local response to the pathogen takes place. This means that the cells of the immune system fight it at the site of occurrence – most often precisely in the intestines with the help of the immune response of the intestinal mucosa.
However, there is also growing talk of the impact of the microbiome (and the entire gastrointestinal tract) on systemic immunity – that is, the one that definitely goes beyond the gut. Gut microbes, their proportions and the effect they have on the body can be of great importance for the functioning of the body’s entire immune system.
Mechanisms of interaction between the gut and immunity
The operation of the immune system is relatively complex and relies on a network of physiological connections between organs and systems. Gut microbes subtly or decisively act on this network of connections and either support or disrupt the immune system. Here are the mechanisms by which the gut (and the microbes that inhabit it) and the immune system interact:
- The intestines are a protective barrier
The intestines act as a physical barrier to protect the body from pathogens and toxins that can enter the body with food, for example. The first line of defines is the intestinal mucosa. It produces mucus that forms a physical barrier preventing unfavourable substances from entering the bloodstream. Another component of this barrier is the enterocytes – cells of the intestines that limit the penetration of unwanted substances by adhering tightly to each other. Also present in the intestines are Paneth cells, which produce special peptides involved in the body’s defence reactions.
- Microbes are involved in the immune response
The gut microbiome, which is all the bacteria and microorganisms that naturally reside in the gut, is also involved in the body’s immune response. They affect the activity of immune cells, such as macrophages, T lymphocytes and dendritic cells. Thus, they indirectly support pathogen identification and control.
- Gut bacteria produce anti-inflammatory substances
A well-functioning gut microbiome produces metabolites that support epithelial function, such as the short-chain fatty acids (SCFAs) – acetate, butyrate and propionate. They have anti-inflammatory effects and support the regeneration of the intestinal epithelium. As a result, they support the function of the mucosa and the body’s natural protection against the entry of pathogens. In simple terms, we can say that with SCFAs the microbes “feed” the environment they inhabit.
- Monitoring role of the gut immune system (GALT)
The intestinal walls contain a large number of immune cells that make up the so-called gut-associated lymphoid tissue (GALT). It is a lymphoid tissue that “monitors” substances passing through the intestines and decides whether to trigger an immune response. The GALT is the largest cluster of lymphoid tissue in the entire body and consists of, among other things, lymphocytes that secrete antibodies, M cells and Peyer’s patches which detect potential threats. Thanks to the efficient functioning of the GALT system, the body is able to effectively distinguish between harmless external factors (such as food) and bacteria and viruses that threaten the body’s safety. The intestinal immune system is also involved in limiting excessive reactions, which can manifest themselves, for example, in food allergies or even autoimmune diseases.
Gut bacteria synthesise vitamins
The gut microbiome also plays a key role in the internal production of certain vitamins that are essential for the body to function properly and provide good immunity. Intestinal bacteria in the colon primarily synthesise vitamin K and some B vitamins. They have anti-inflammatory effects, support immune cell metabolism and generally improve the health of the entire body. In order for vitamin synthesis to actually occur in the gut, the microbiome and its composition must be taken care of.
How to support immunity by taking care of the gut?
Simply enriching the diet with vitamin C or superfoods may not be enough to effectively support immunity. When taking care of immunity, the role of the gut microbiome cannot be overlooked. Here are 12 specific tips to ensure a healthy and diverse composition of gut microbes, thereby supporting the immune system:
- Eat fibre (especially soluble fibre)
Soluble fibre is literally food for intestinal microbes. Theoretically, fibre is an indigestible dietary fibre that does not directly provide energy to our body cells, but can nourish intestinal microbes. For this reason, fibre is extremely necessary for the proper functioning of the intestines and the right composition of the microbiome. Which products have the most fibre?? These are mainly whole-grain cereal products, legumes, nuts, fruit and vegetables. Soluble dietary fibre fractions such as beta-glucans, pectin, gums and mucus, for example, work best as a medium for gut microbes. Here is a list of products particularly rich in this type of fibre, which nourishes intestinal bacteria and most effectively, indirectly, supports immunity:
- flaxseed (27.3 g of fibre, including 1 g of soluble fibre),
- oat flakes (10.6 g of fibre, including 3.0 g of soluble fibre),
- oat bran (15.4 g of fibre, including 3.6 g of soluble fibre),
- dried apricots (7.3 g of fibre, including 1.4 g of soluble fibre),
- chia seeds (34.4 g of fibre, including 1.1 g of soluble fibre),
- figs (9.8 g of fibre, including 1.9 g of soluble fibre),
- apples (2.4 g of fibre, including 0.6 g of soluble fibre),
- citrus (2.2 g of fibre, including 0.4 g of soluble fibre),
- legumes (beans, lentils, chickpeas – 6.4 g of fibre, including 2.2 g of soluble fibre),
- pears (3.1 g of fibre, including 1.0 g of soluble fibre),
- broccoli (2.6 g of fibre, including 0.5 g of soluble fibre),
- dried prunes (7.1 g of fibre, including 1.8 g of soluble fibre).
Dietitian’s tip: Ensure that your diet contains at least 25-30 g of fibre per day.
- Avoid processed food
A typically Western diet rich in saturated fat, sugar, trans fatty acids and excess salt does not support the health of the gut microbiome. It promotes the growth of Candida fungi, increases inflammation and reduces the number of beneficial bacteria. Regular consumption of processed food leads to depletion of the gut microbiome, dysbiosis, inflammation and weakening of the intestinal barrier. These are unfavourable conditions for the functioning of the immune system.
- Choose a variety of foods to diversify the microbiome
Despite many studies, scientists are still not sure what the ideal composition of the gut microbiome is. It is certainly known that some bacterial strains are more desirable than others, but in determining “whether the microbiome is healthy”, what matters most is the degree of species diversity of gut bacteria. In simple terms, we can say that the more diverse bacteria inhabit the gut, the healthier the entire microbial ecosystem.
How to increase the microbiome’s diversity? It is not at all necessary to introduce specific strains through expensive probiotic therapy (although this can be useful in some cases). The best way is to increase the variety of food consumed. Different species and subspecies of gut bacteria prefer different products. A monotonous diet is a simple path to a poorly diversified microbiome. Above all, it is worth ensuring the wealth of plant-based food (and thus the variety of dietary fibre consumed). Experts estimate that it is worth eating at least 40 different plants per week. How to implement this recommendation in practice?
- Eat colourful salads – mix fruit, vegetables, groats, seeds and nuts to expand the range of food products.
- Reach for mixed vegetables – such as frozen stir-fry vegetables or frozen mixes for soups. You can easily incorporate them into your diet and increase the number of plant-based products you consume.
- Opt for sprinkles – black cumin for sandwiches, sesame to sprinkle on pasta, almond flakes for oatmeal, sunflower seeds for cream soup, bran for a smoothie... You can easily incorporate a greater variety of plant-based products into your menu.
- Compose healthy smoothies – blend fruit and vegetables, but also legumes, herbs and spices for additional ingredients to support microbiome diversity.
Read also: Healthy Smoothie Recipes
- Exercise to nourish microbes
Regular physical activity significantly supports building a healthy gut microbiome and immune system. Activity does not have to be intense or burn a lot of calories in order to be effective. Even a daily walk improves blood circulation (including blood in the intestines) and reduces stress levels. This contributes to more efficient digestion of food and support of intestinal bacteria. It is worthwhile to use regular physical activity: from walking, swimming and strength training, to rollerblading or practicing yoga. Any form of activity is valuable for the gut and building immunity.
- Enrich your diet with natural pro- and prebiotics
Natural sources of probiotics and prebiotics are great for the composition of the gut microbiome and can support natural immunity. Enrich your diet with the following ingredients:
- pickles: cucumbers, cabbage, kimchi, beet sourdough,
- fermented dairy products: buttermilk, yoghurt, cottage cheese, leben,
- kombucha,
- sources of inulin, such as chicory, Jerusalem artichoke, garlic and onions,
- prebiotic legumes: lentils, beans, chickpeas.
They have a very positive effect on the gut and immunity. They should often be on the plates, especially in the autumn and winter.
Read also: Diet for a healthy gut
- Avoid stress
Excessive stress negatively affects the entire body, including the gut microbiome. Long-term stress disrupts the balance of microorganisms in the gut, thus weakening the body’s immunity. The connection between the intestines and the brain plays a key role, with some studies suggesting that gut bacteria can directly regulate the secretion of cortisol, the stress hormone. So try to maintain work-life balance, incorporate relaxation techniques, practice meditation. Physical activity to reduce stress levels will also help.
- Bet on quality sleep
Sleep is a time for recovery of the entire body, including the intestines. Sleep deprivation and inadequate sleep hygiene can lead to disruption of the microbiome. This is supported by scientific studies, which noted that sleep deprivation even led to intestinal dysbiosis. Therefore, not having proper nightly rest is one of the most important factors lowering immunity.
- Drink the right amount of water
Drinking an adequate amount of fluids (especially water!) every day is key to keeping the body healthy. Common effects of dehydration include weight loss problems, headaches and sluggishness. Few people remember, however, that water is crucial to maintaining the health of the digestive system, including the gut and microbiome. Water plays an important role in:
- the process of digestion and absorption of food,
- supporting intestinal peristalsis and preventing constipation, which can promote the overgrowth of undesirable intestinal bacteria,
- maintaining optimal pH in the intestines and the entire digestive tract,
- regular removal of toxins and other unwanted substances from the intestines.
Tip: The healthiest liquid in terms of health of the gut microbiome is water, but it can be partially replaced by tea, coffee and herbal infusions. Drinking beverages with sugar and sweeteners has controversial effects on gut health and is rather not recommended.
- Avoid controversial food additives
Among food additives, there are some whose effects on the gut microbiome are controversial or not fully understood. These ingredients have no explicitly proven negative effects, but isolated cases suggest that they may be affecting the microbiome (and it is more likely a negative impact). Such substances include sweeteners (especially sucralose, saccharin, aspartame), emulsifiers and carrageenan.
It is suspected that sweeteners may disrupt the natural metabolic activity of intestinal bacteria, and carrageenan may adversely affect the intestinal epithelium. Emulsifiers are suspected of affecting the epithelium and intestinal mucus. It is worth noting that these are not clearly negative conclusions. However, one should be aware of the controversy and not consume too much processed products very rich in such ingredients. They are found, for example, in popular protein puddings, plant-based drinks, ice cream or protein snacks.
- Avoid unnecessary antibiotics and drugs
Antibiotics fight microbes, and this effect is often not selective. Along with pathogenic bacteria, health-supporting elements of the gut microbiome are also lost with antibiotic therapy. Of course, in many cases, antibiotics are necessary for effective treatment, but take them only under doctor’s supervision and with a clear recommendation. Uncontrolled antibiotic therapy can upset the microbiome’s composition and lead to immunity problems.
It is not just antibiotics that affect the microbiome. Other drugs also influence the gut microbiota and the intestinal barrier: proton pump inhibitors, non-steroidal anti-inflammatory drugs, iron preparations or the popular metformin. Use them under close supervision of a doctor and knowing that they can affect the intestinal microflora, which is worth additional support during therapy.
- Reach for targeted probiotic therapy if needed
Well-chosen probiotics can have great health effects, but it makes little sense to recommend probiotics “blindly”. A probiotic should be selected for a specific purpose and target the right strains and dosages. Here are some mechanisms for supporting the immune system through targeted probiotic therapy:
- enhancing the activity of immune cells (macrophages and granulocytes),
- activating Natural Killer cells that support the elimination of cancerous and virus-infected cells,
- modulating the activity of pro-inflammatory cytokines.
However, this is only a theoretical effect of selected bacterial strains, most often confirmed only by laboratory tests. Probiotic therapy can definitely work to support the health of the microbiome, but the research conducted leads to little practical conclusions that can rarely be turned into general recommendations.
In the context of strengthening immunity to seasonal infections, the greatest efficacy has been shown for the Lactobacillus Rhamnosus LGG bacterial strain. Taking probiotics with this strain in studies reduced the risk of upper respiratory tract infections by up to about 40%.
- Act regularly
Building immunity can take months or even years. Do not count on the described methods to bring immediate results. It is best to start thinking about supporting immunity before health problems arise. In order for all the methods indicated above to work, you need to develop consistent habits for a healthy lifestyle, including a balanced diet rich in plant-based foods and fibre, moderate activity, relaxation and avoidance of stress.
Remember that building immunity to autumn infections starts as early as summer, and even earlier. The gut microbiome is a complex ecosystem that requires constant support and a healthy lifestyle. Ad hoc measures may not be enough.
References:
Wiertsema S. P., van Bergenhenegouwen J., Garssen J., Knippels L. M. J., 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, 2021 Mar 9;13(3):886, doi: 10.3390/nu13030886, PMID: 33803407; PMCID: PMC8001875.
Yoo J. Y., Groer M., Dutra S. V. O., Sarkar A., McSkimming D. I., Gut Microbiota and Immune System Interactions, Microorganisms, 2020 Oct 15;8(10):1587, doi: 10.3390/microorganisms8101587. Erratum in: Microorganisms, 2020 Dec 21;8(12):E2046, doi: 10.3390/microorganisms8122046, PMID: 33076307; PMCID: PMC7602490.
Princivalli M. S., Paoletti C., Magi G., Palmieri C., Ferrante L., Facinelli B., Lactobacillus rhamnosus GG inhibits invasion of cultured human respiratory cells by prtF1-positive macrolide-resistant group A streptococci, Lett Appl Microbiol, 2009 Mar;48(3):368-72, doi: 10.1111/j.1472-765X.2008.02540.x. Epub 2009 Jun 23, PMID: 19187508.