The gut is where the microbiomes and immune system meet. The immune system is a complex network of disease-fighting cells that protect the body from harmful antigens and toxins released by pathogens, including bacteria, viruses, parasites, and other microorganisms. About 70 per cent of the immune system is located in the gut and so keeping the gut healthy is crucial for the immune system to perform optimally.
The gut microbiota that houses the gastrointestinal tract has a major say in maintaining immune homeostasis and managing health outcomes. The alterations in gut microbiota culture are responsible for immune dysfunction, production of toxins, inflammation, and autoimmune disorders.
A 2020 review published in Cell Research mentions that microbiome-immune system crosstalk is associated with a variety of non-communicable and autoimmune diseases including inflammatory bowel disease, celiac disease, rheumatoid arthritis, metabolic syndromes, neurodegenerative disorders, and malignancy.
Poor nutrition and immune system
The relationship between diet and the immune system is bidirectional. What we eat every day has a huge impact on inflammation, gut microbiome balance, gut barrier function, and disease outcome. A growing body of evidence explains the link between the quality of diet, gut health, and immunity.
A western-style diet usually contains a high amount of trans fatty acid, refined carbohydrates, ultra-processed foods, salt, additives and lacks healthy food groups such as colorful vegetables, low sugar fruits, fish, protein, antioxidants. This type of diet, along with overeating and a sedentary lifestyle, was found to be linked with chronic inflammation that leads to non-communicable diseases and alters the immune system.
Ultra-processed foods are deficient in multiple micronutrients, many of which, like vitamin D, zinc, selenium, vitamin C, and B vitamins, are essential for optimal immune function. Sugary fruits and drinks – cakes, candy, processed cereals, and fruit juices are linked to leaky gut syndrome and promote the growth of pathogens in the gut and eliminate beneficial bacterial colonies. It also adversely altered gut microbiota thus promoting inflammation. Excess added salt was found to trigger or worsen certain autoimmune disorders, including rheumatoid arthritis.
Researcher Mohammad Iddir and colleagues address the importance of an adequate status of crucial nutrients to effectively reduce inflammation and oxidative stress, thereby strengthening the immune system during the Covid-19 crisis. The authors also mention that a poor diet was associated with an increased level of inflammatory proteins including tumour necrosis-alpha (TNF-alpha), C-reactive protein (CRP), and interleukin-6 (IL-6).
Also Read: Are you gaining weight? Get gut-healthy
What to eat for a healthy gut?
Keeping your tummy happy is extremely important for a well-functioning immune system. A diverse range of diets with colorful vegetables, low-sugar whole fruits, beans, legumes, whole grains, proteins, and probiotics help maintain diversity in gut microbiome culture. For example, people from rural regions of Africa and South America consume a diverse diet thus possess a better gut microbiome diversity than people from urban areas in Europe and United States as reported by researchers from Italy and the US.
The Mediterranean diet is beneficial for the gut and immune system. This diet is composed of vegetables, legumes, nuts, fruits, whole grains, olive oil, fish, and other nutritious foods that make it rich in antioxidants, polyphenols, unsaturated fatty acids, vitamins, and minerals. Research has linked a Mediterranean diet to protect against diseases caused by chronic low-grade inflammation, including cancer, diabetes, obesity, atherosclerosis, metabolic syndrome, and cognitive impairment. Following a long-term Mediterranean-style diet has demonstrated a beneficial modulation in gut microbial cultures in humans as well as in experimental animal models such as rodents.
The Mediterranean diet
Mediterranean diet is also rich in fiber, ideal for the gut microbiome. Dietary fiber gets fermented by the gut microbiome and produces short-chain fatty acids (SCFAs) – acetate, propionate, and butyrate as end products. SCFAs are crucial to modulate the immune response and maintain the immune defensive function of the intestinal epithelium.
Eating more plant-based food ensures adequate gut-friendly nutrients in your daily diet. Plant-based, flexitarian diets include fruits, green leafy vegetables, olive oil, nuts, seeds, and also allow eggs, fatty fish, lean protein. These food groups are rich in antioxidants, vitamins and minerals – vitamin A, vitamin C, zinc, vitamin E, B6, B12, copper, folate, iron, and selenium, which are crucial to support the immune system.
Plant-based diets are also rich in polyphenols, beneficial plant compounds that help lower blood pressure, inflammation, oxidative stress and promote heart, brain, and gut health. Polyphenols directly reach the colon and are digested by gut bacteria thus have a beneficial role in modulating gut microbiota composition and function. Foods that are rich in polyphenol are – green tea, almonds, red grapes, onions, berries, broccoli, cocoa, and sugar-free dark chocolate. A 2020 study reported that polyphenol from cocoa promotes the growth of beneficial gut bacteria, such as Lactobacillus and Bifidobacterium, while reducing the number of pathogenic ones, such as Clostridium perfringens. However, dark chocolate and other cocoa-containing foods are usually high in refined sugar and need to be eaten in moderation.
Probiotic foods such as Greek yogurt, kefir, sauerkraut contain beneficial “living microorganisms” that exhibit a preventive and therapeutic effect by protecting gut lining, maintaining internal microbial balance, and both adaptive and innate immunity.
The human gut is the home of multi-functional microorganisms, collectively known as the gut microbiota. These microbiomes work synchronously with human cells to produce maximum health benefits to the host. Gut microbiomes play a critical role in controlling almost all crucial physiological phenomena including inflammation, metabolism, appetite, mood, neurological outcome, psychological disorders, metabolic syndromes, and immunity. Maintaining a healthy gut by eating a diverse, whole-food-based diet along with regular physical activity is recommended for optimum health promotion, preventing critical illnesses, and overall wellbeing.
Subhasree Ray is Doctoral Scholar (Ketogenic Diet), certified diabetes educator, and a clinical and public health nutritionist. She tweets @DrSubhasree. Views are personal.
This is the last article of a three-part series on gut health. The first article focused on the relationship between the gut and weight gain. The second article on the relationship between the gut and mental health.
(Edited by Srinjoy Dey)