Your gastrointestinal (GI) tract is home to tens of trillions of micro-organisms, both good and bad. And this massive community of microbes decides how healthy you are.
This enormous collection of bacteria, virus and fungi living in your intestine forms your gut microbiota. This dynamic population of micro-organisms not only determines your gut health but also affects your nutrition status, mood and immune function.
The gut microbiota is involved in regulating various functions as it:
- Helps in digestion
- Promotes absorption of nutrients
- Helps in synthesis of nutrients like vitamin K and folic acid
- Produces short-chain fatty acids (SCFA) that protect gut mucosa and reduces inflammation
- Strengthens gut integrity and supports a healthy gut barrier
- Keeps pathogens in check
- Helps in detoxification
- Regulates immune function
- Regulates inflammation
Your body needs to maintain the right balance of healthy and harmful bacteria. Any shifts or imbalance in the gut microbiota leads to gut dysbiosis, which is very closely tied to poor immunity, autoimmune disorders, obesity, mood disorders, anxiety and various other diseases. On the other hand, the right balance can also positively influence your health in several ways.
Link between gut bacteria and immunity
The bacteria living in your intestine plays a big role in maintaining immune functions. So, how does gut health affect your immunity? How does that really work?
Your gut microbiota communicates with the brain and central nervous system to regulate a lot of functions and that includes digestion, metabolism, production of hormones, immune function and how you respond to stress.
The bacteria begin to colonize your GI tract right from birth. Many experts believe that this sets the tone for one’s health in the coming years. In fact, emerging research suggest that a baby can inherit a mother’s microbes before they are born.
For babies born vaginally, the mother passes the bacteria on to the baby. This activates the baby's immune system. However, things get a little different in children born through C-section, where this handing down of bacteria is impacted.  Experts believe this could be why C-section babies are generally more vulnerable to developing allergies, asthma, chronic inflammatory diseases, obesity and even diabetes in later years.
A 2018 study shows that the way in which a baby is delivered influences the development of microbiota and the immune system through various means. 
In addition, mother’s milk also plays a key role in the process, where it not only provides nutrition to the baby but also contains various bioactive and immunity-related components that help build the composition of microbiota. A number of studies show that babies who are breastfed have a healthier gut and a better immunity in comparison to those who are only formula fed.
This population of bacteria that you inherit from birth becomes more diverse as you grow and are exposed to different types of microbes through foods, infections and environment. The Guardian explains that our gut microbiome goes through a lot of changes in the first two years, but soon becomes stabilized. However, your dietary choices, stress, excessive use of drugs and antibiotics, inadequate sleep and age keep changing the composition and diversity of your microbiota – affecting your immunity and overall health.
So, how does the bacteria in your gut build and shape your immunity? Scientists are still working on putting together this piece of the puzzle, but you can say your microbiota send signals through hormones and chemicals to train your immune system.
The function of your immune system is to maintain a tight balance between fighting and controlling harmful pathogens and building tolerance to beneficial organisms. And the microbial community living in your gut helps develop and activate immune cells such as T cells. It educates T cells to differentiate between foreign invaders and the body’s own healthy bugs and tissues. It is also believed that some cells in the gut lining specialize in releasing large amounts of antibodies.
The gut bacteria also help in the production of molecules called short-chain fatty acids (SCFAs) such as butyrate. These molecules are formed when gut bacteria ferment non-digestible carbohydrates. SCFAs serve as a food source to the bacteria residing in the gut but they also regulate immune function, protect the mucosal layer of your intestine and help maintain the gut barrier, which is extremely important for controlling inflammation, food sensitivities and autoimmunity. Studies show that inadequate production of SCFAs is associated with obesity and type 2 diabetes.
Gut imbalance and leaky gut
There is another way your gut health is linked with immunity.
The lining of your intestines absorbs nutrients, but it is selective about the particles that can enter the bloodstream. A healthy gut lining has tight junctions that do not allow toxic waste, bacteria and undigested food particles to get out. In some people, this lining may become damaged and its small gateways develop large spaces – causing undesirable content from the gut to slip into circulation. Chronic stress, zinc deficiency, vitamin D deficiency, poor dietary choices, antibiotics, chronic infections and excessive drinking can cause leaky gut.
With this, your immune system gears up. It creates antibodies and triggers inflammatory reactions, leading to chronic inflammation and pain. It can even lead to abnormal immune responses and your immune system begins to attack your body’s own healthy tissues – leading to autoimmune disorders, allergies and food sensitivities.
What you need is a well-balanced and diverse microbiota
To establish appropriate, well-balanced immune responses, which means different types and species of bacteria and other micro-organism in your gut, you need a diverse microbiota. Studies show that people with rheumatoid arthritis, psoriasis, diabetes, celiac disease, obesity, inflammatory bowel disease and arterial stiffness have gut microbiota that is less diverse than those in healthy people.
Studies also show that in high-income developed countries, factors like overuse of antibiotics and dietary habits may have contributed to a bacterial composition that doesn’t have the diversity and flexibility that you need to establish a balanced immunity. This could be why there has been a sharp rise in chronic, inflammatory and autoimmune disorders in some parts of the world. 
The composition and diversity have a strong influence on your immune function as well as metabolism, mood and even heart health. For example, a recent research published in the European Heart Journal, revealed a link between the gut bacteria and stiffening of arteries, further suggesting that altering the microbiota through diet and probiotic supplements creates new possibilities in reducing the risk of heart diseases, especially when this risk cannot be explained by typical risk factors. 
Did you know your microbiota influences effectiveness of vaccines?
Emerging research suggest that the diversity and composition of your gut microbiota determines how well your body responds to vaccines.  When you have gut dysbiosis and leaky gut, your immune system is already busy launching attacks against the toxins, bacteria and fungi that have found their way in the bloodstream.
What can you do to maintain gut health?
1. Choose your diet carefully
Your diet plays a very crucial role in establishing how healthy and resilient your gut health is. A diet loaded with sugars, unhealthy fat and highly proceeded foods bursting with artificial colors, perseverative and other chemicals reduce the amount and diversity of friendly bacteria in the gut. On the other hand, fresh and whole foods like vegetables, fruits and sprouts protect the friendly bugs. These foods are also rich in vitamins, minerals, antioxidants, fibre and digestive enzymes. Fibre from raw, whole foods not only cleanses your intestines but also feeds and nourishes healthy bacteria, helping them grow.
2. Add more probiotics in your diet
Probiotics are live, healthy bacteria that restore the make-up and diversity of your gut microbiota. Foods such as kimchi, yoghurt, sauerkraut and kombucha are some great sources of probiotics that not only introduce healthy bacteria in your gut but also contain digestive enzymes that you need for optimum intestinal health.
3. Don’t forget prebiotics
While you need probiotics for your gut health, these beneficial germs need their nutrition to grow. And that’s where prebiotics come in to the picture. Prebiotics are carbohydrates that your body is not able to break-down. The friendly bugs in your gut feed on these undigested carbohydrates. This process also results in the formation of short chain fatty acids. Foods like bananas, leeks, onions and asparagus naturally contain prebiotics.
4. Take antibiotics only when necessary
Cold and flu are caused by a virus and antibiotics cannot control a viral infection. Take antibiotics only when it is absolutely necessary, as it kills both the good and bad bacteria without any discrimination. Some dairy products and meat are also loaded with antibiotics, depleting healthy bacteria from the gut.
5. Reduce systemic inflammation
While poor gut health leads to leaky gut and inflammation, systemic inflammation also causes imbalances in the microbial ecosystem. If you have inflammation, supplements such as curcumin and omega-3 fatty acids may help. In addition, if you are looking to reduce inflammation, cut down on sugar and refined carbs, quit smoking, drink plenty of water, sleep well and manage your stress.
6. Manage stress
Chronic stress is known to deplete good bacteria, alter your gut composition and create inflammatory environment in the body. This causes the gut lining to weaken, making you prone to leaky gut, nutritional deficiencies and disease. Chronic stress changes the way your gut interacts with your brain. This leads to a wide range of gastrointestinal complications such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), peptic ulcer and gastroesophageal reflux disease (GERD). 
7. Sleep well
You need quality sleep to rejuvenate and repair from daily wear and tear. What’s more, sleep is closely related to your gut and immune health. It appears that your circadian rhythms also affect the rhythm and function of the micro-organisms in the gut.
And it works both ways. Sleep deprivation affects your gut bacteria and reduces the number and types of helpful microbes. These changes are associated with weight gain and other metabolic disorders. On the other hand, poor gut health may cause poor sleep. It is because the bacteria in your gut are involved in the secretion of hormones that foster calm and sleep. Just like your brain, your gut microbiota plays a key role in releasing neurotransmitters such as melatonin, serotonin and dopamine.
8. Up your zinc intake
Zinc deficiency affects digestion and gut health. Studies show that low zinc status triggers leakiness in the tight junctions across the intestinal lining. Improving your zinc intake enhances your gut barrier function and reduces intestinal permeability, also called leaky gut. Zinc supplements can help heal the gut and provide relief to people suffering from Crohn’s disease and Colitis.
9. Exercise regularly
Moderate exercise is good for your gut. A study found that exercise can change the composition and function of your gut microbiota. It increases the population of friendly microbes, which also means reduced inflammation. According to the researchers, this positive effect was irrespective of the diet. It appears that physical activity changes the amount of micro-organisms that produce short chain fatty acids, such as butyrate.  Exercise is also good for sleep and managing stress, two important components that feature in your gut health and immunity.
And Get Dirty
Yes, you read the correctly. Encourage your kids to get down and get dirty to have a healthy introduction to all kinds of bacteria, which then trains and builds up the immune system. Engage more in outdoor activities that expose your body to microbial loads found in soil and the environment around us. A diverse gut flora is important for a more tolerant and sturdy immune system. Excessive use of anti-bacterial soaps and products also wipe out good bacteria, giving rise to an immune system that is less resilient in the face of infections and allergies.
- Wampach et al. Birth mode is associated with earliest strain-conferred gut microbiome functions and immunostimulatory potential. Nature Communications. 2018
- Francino M.P. Birth Mode-Related Differences in Gut Microbiota Colonization and Immune System Development. Nutrition and Metabolism. 2018
- Belkaid et al. Role of the Microbiota in Immunity and Inflammation. Cell. 2014
- Menni et al. Gut microbial diversity is associated with lower arterial stiffness in women. European Heart Journal. 2018.
- Valdez et al. Influence of the microbiota on vaccine effectiveness. Trends in Immunology. 2014.
- Konturek et al. Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options. Journal of Physiology and Pharmacology. 2011.
- Allen et al. Exercise Alters Gut Microbiota Composition and Function in Lean and Obese Humans. Medicine & Science in Sports & Exercise. 2017