In the current scenario of Corona pandemic, immunity has become the primary key to fight against the infection. Currently, there are several hygiene practices that are crucial to prevent the risk of COVID-19. Just like protecting yourself from the virus on the outside, it is important to boost your immunity from inside to defend the virus. With continuing spread of Coronavirus, the best weapon in our hand is our immunity.
Our gut is a home for several microbes, which plays an important role in regulating the health of immune system. Interestingly, recent studies have proved a connection between the gut microbiota and lung diseases. Also, some studies stated that, a huge proportion of our immune system lies in our gastrointestinal tract. Considering these evidences, scientists reported that nurturing gut microbes and maintaining digestive wellness could prevent the pro-inflammatory immune reactions to COVID-19.
Digestive Wellness and Immunity - A Surprising Link
Through research, it is now a well-established fact that digestive system and immune system are closely linked to one another . Evidences are accumulating to further strengthen this link, and health experts are starting to believe that good health and well-being depends on the healthy gut. Indeed, our guts control every aspect of our health in the way how we digest our food and how our food sensitivities are linked with our mood, behavior, energy, weight, food cravings, hormone balance, immunity, and overall wellness. 
Our digestive system comprises of all the organs from mouth to the large intestine, which help in ingestion of food, absorption of water and other nutrients from the food. A suboptimal function of the digestive system may lead to diarrhea, constipation, bloating, acidity, infectious and autoimmune diseases. Our immune system is responsible to fight against infections and protect us from diseases.  The immune system is made up of several glands, different types of cells and chemical mediators that can evoke an immune response against a foreign invader. Earlier considered as different entities, these systems are now being viewed as an inter-related system . A suboptimal function of one system can result in the other system becoming dysfunctional. 
The Newly Found Gastrointestinal Immune System
Lymphoid tissues and lymph nodes are important components of the immune system, and these are very much present in our gut lining. These contain several kinds of immune cells including activated T-cells, plasma cells, mast cells, dendritic cells and macrophages. It is collectively known as the gut-associated lymphoid tissue (GALT). In fact, the number of lymphocytes in the GALT is close to those present in the spleen (lymphatic organ). Additionally, the lining of the intestine that were solely thought as made of absorptive cells are now identified as an important component of the immune system . Each day the gastrointestinal tract encounters a number of potentially harmful pathogens through ingested food. These encounters help the immune cells to mature, and in future when these immune cells get translocated to other body systems, can launch an effective response against the same. Additionally, the immune cells present in the gastrointestinal tract prevent the growth of these pathogens and foreign bodies that are ingested along with the food. 
Our gut is also populated with bacteria, fungi and viruses known as gut microbiota. Apart from producing essential vitamins and promoting digestion, they influence our immune system . Gut microbiota can also modulate the expression of various genes in gastrointestinal tract, including the ones involved in nutrient absorption, energy metabolism and most importantly those involved in immunity. 
The characteristic of an effective immune system is to differentiate between normal self-tissues and pathogenic microbes and selectively eliminate them. Gut bacteria play an important role in this process through digesting fibre and turning it into smaller molecules known as short-chain fatty acids (SCFAs). These SCFAs can control various cells and functions in the body including that of the T-cells, a type of immune cells. The gut microbiota interacts with T cells directing them whether to act upon or spare the cells. Hence, the delicate balance between the essential gut microbiota helps to improve immunity. [14,15,16]
It is known that gut microbiota is unique for every individual and helps to keep our gut healthy. Needless to say, our diets have profound effect on our gut microbiota. The food we take can be beneficial to the bacteria; on the other hand, some kinds of food can also harm the fragile gut bacteria. In fact, the balance of different bacterial species in the gut can influence the immune response [7,8].
Gut microbial manipulation achieved through administration of probiotics or fecal microbiota transplantation is found to be beneficial in the treatment of serious conditions in children, such as necrotizing and acute infectious diarrhea, antibiotic-associated diarrhea, ventilator-associated pneumonia etc .
A Healthy Gut For A Strong Immune System
It is known that gut microbiota is unique for every individual and is responsible for gut health. Hence, foods that promote the growth of good bacteria keeps the gut healthy .
There are some foods that improve both gut and general health. Including fresh fruits, vegetables and foods that are rich in fiber such as beans in the diet helps to promote good bacteria in the gut. Choosing fermented food and probiotics are also good ways to promote good bacteria. Consuming good amount of probiotics help to reduce the chances of stomach infections due to food allergies. However, research on health benefits of probiotics and their use is still emerging. In contrast, refined and fried foods can be detrimental towards gut microbes and can create imbalance between the essential bacteria. 
Experts also recommend eating foods, such as cloves, cocoa powder, berries, nuts, and soy. These foods are rich in polyphenols that help to improve the gut microbiota. Such foods help to maintain the digestive system in its best possible condition, thereby boosting the immunity . Additionally, exercise, enough sleep and a check on stress levels also plays an important role in improving gut and overall health.
Digestive problems can be the underlying cause for allergies, arthritis autoimmune disorders like irritable bowel syndrome, acne, chronic fatigue, autism, dementia and even cancer.  In fact the rising global incidence of autoimmune and inflammatory conditions can be linked to the changes in the dietary practices of modern living.  Therefore, to keep our immune system in it best function, it is important to pay attention to our digestive health, and east foods that are healthy for the gut .
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- Bell V, Ferrão J, Pimentel L, Pintado M, Fernandes T. One Health, Fermented Foods, and Gut Microbiota. Foods. 2018;7(12):195.
- Broderick NA. A common origin for immunity and digestion. Front Immunol. 2015;6:72. Published 2015 Feb 19.
- Hashemi Z, Fouhse J, Im HS, Chan CB, Willing BP. Dietary Pea Fiber Supplementation Improves Glycemia and Induces Changes in the Composition of Gut Microbiota, Serum Short Chain Fatty Acid Profile and Expression of Mucins in Glucose Intolerant Rats. Nutrients. 2017;9(11):1236.
- Harris VC, Haak BW, Boele van Hensbroek M, Wiersinga WJ. The Intestinal Microbiome in Infectious Diseases: The Clinical Relevance of a Rapidly Emerging Field. Open Forum Infect Dis. 2017;4(3):ofx144.
- Lazar V, Ditu LM, Pircalabioru GG, et al. Aspects of Gut Microbiota and Immune System Interactions in Infectious Diseases, Immunopathology, and Cancer. Front Immunol. 2018;9:1830.
- Yap YA, Mariño E. An Insight Into the Intestinal Web of Mucosal Immunity, Microbiota, and Diet in Inflammation. Front Immunol. 2018;9:2617.
- Belkaid Y, Hand TW. Role of the microbiota in immunity and inflammation. Cell. 2014;157(1):121-141.
- Parada Venegas D, De la Fuente MK, Landskron G, et al. Short Chain Fatty Acids (SCFAs)-Mediated Gut Epithelial and Immune Regulation and Its Relevance for Inflammatory Bowel Diseases [published correction appears in Front Immunol. 2019 Jun 28;10:1486]. Front Immunol. 2019;10:277.
- What is Epigenetics. https://ghr.nlm.nih.gov/primer/howgeneswork/epigenome. Accessed on 3rd July 2020.
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