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Why Is Gut Health Important For Immunity?

Your immune system is your own little in-built defence force. It’s an amazingly detailed system of responses, coordinated throughout our body, to protect us from all kinds of invasions and disease. Understanding it can help us to maintain an optimum immune response in a world of fast-evolving viruses and bacteria threats.

Your immune system is your in-built defence force against viruses and bacteria. Photo: Derek Morrison

Did you know that most of the body’s immune cells are in our gut? Therefore understanding your immune system starts in the gut. We are learning so much about how various gut bacteria operate to, hopefully, improve our defences against those sneaky pathogens – the viruses and bacteria that can make us ill. Most of us are guilty of taking our immune system for granted.

Your microbiome, or the community of mainly bacteria present in your gut, form a competitive barrier to disease-causing pathogens. Each of us has our own unique “signature” comprising of the type of bacteria that live in our gut and how many of each type we have. Most of these bacteria live in our lower bowel, or colon. We know that if we look after those protective bacteria, they can look after us better. It’s a symbiotic relationship that we tend to completely ignore.

Know your prebiotics from your probiotics

You may have heard of probiotics in foods and supplements. Probiotics are beneficial live bacteria or yeast. To have any benefit though they need to survive the somewhat challenging journey through your digestive tract, to be available to colonise in your gut. There are many different types of probiotic bacteria strains. We are only just beginning to learn which strains help us and in which ways. We do know that diversity of bacteria is a good thing.

Prebiotics on the other hand help your own existing bacteria by providing the food that they need to flourish. When we eat certain types of carbohydrates that are resistant to digestion in our upper bowel, the bacteria can ferment those carbohydrates as their own fuel. They produce short-chain fatty acids (SCFA), particularly acetate, proprionate, butyrate and lactate as they ferment the carbohydrate. These SCFA are then taken up from our gut into the liver or bloodstream and impact our health. Butyrate is particularly beneficial for us.

The typical high-fat, high-sugar, low-fibre Western diet does not promote the growth of beneficial bacteria in our gut. It reduces the diversity of bacteria living in the colon. This eating pattern can create extra stress on our body that the immune cells in our gut immediately react to – causing chronic, systemic, inflammation. A poor diet can also open up the tight junctions between the gut membrane cells, making it easier for pathogens to enter our body; leaving us feeling ill, stressed, and miserable.

How can we improve our gut health?

The simplest strategy is to eat more fibre. A high-fibre diet prevents pathogenic bacteria from accessing your gut lining. Resistant starch is really the buzz word here. It is a type of starch that is resistant to digestion in our stomach and upper intestine, hence the name. Because we cannot digest it easily, there is still food left available by the time that resistant starch hits our lower bowel, where all our good bacteria live. And they love it. Table 1 lists some resistant starch sources that are great food for our gut bacteria to thrive on.

Table 1: Food Sources Of Resistant Starch

Green banana, plantain, inulin (found in many fruits, vegetable and herbs such as, onions, bananas, leeks, artichokes, asparagus and wheat), pasta salad, rice salad, sushi, whole grains and wholegrain breads, kumara, legumes such as, beans, chickpeas, lentils and peas, potato salad, any cold cooked potato, raw oats, taro, cashew nuts, bean salad.

Other probiotic and prebiotic foods include yoghurt that contains live or active cultures, fermented foods such as kimchi, sauerkraut, kombucha (a fermented tea beverage), kefir (a fermented milk drink), miso, tempeh (a fermented soy product), natto (another fermented soy product) and gherkins.

There is plenty of research emerging regarding exercise and gut health. Not surprisingly, exercise positively impacts gut health. Well, really intense exercise can stress the gut a bit at the time, but regular moderate continuous exercise or high-intensity interval training can increase the diversity of our gut bacteria and is most beneficial when we exercise when young.

Exercise also stimulates the movement of immune cells from the lymph into the blood and out to tissues to help us adapt to the stress of that exercise. These include the pretty funky sounding Natural Killer cells – or NK cells – who doesn’t want those on their side? Exercise stimulates and primes the immune system in a healthy way, generally.

However, each winter as the season rolls around antibiotic use increases. Antibiotics, by definition, kill bacteria. Your beneficial gut bacteria are also susceptible to the effects of those antibiotics. If you need to use antibiotics to treat an illness then you should pay attention to your diet in the weeks following treatment to help restore balance of bacteria in your gut. Include lots of vegetables and fruit, plenty of water and foods rich in resistant starch to help your gut and immune system recover.

Luckily, winter is also a season where most of us eat more legumes, a fantastic source of fibre and resistant starch. So feel free to add beans, lentils, peas (including split peas) and chickpeas to your soups and casseroles – your body will thank you for it.

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