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Did you know your immune system is your own little in-built defence force, writes Kirsty Fairbairn?
We often take our immune system for granted. It’s an amazingly detailed system of responses, co-ordinated throughout our body to protect us from all kinds of invasions and disease. It all starts in your gut; we are learning so much about how the various (good and bad) bacteria in our gut operate to improve our defences against pathogens (the viruses and bacteria that make us ill).
Your gut microbiome, meaning the community of (mainly) bacteria present in your gut, forms a competitive barrier to disease-causing pathogens. Each of us has our own unique "signature" of which bacteria 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 ignore.
Emerging research suggests our gut bacteria impact our appetite (there is direct communication between our gut and our brains!) and our chances of being overweight, developing various cancers, type 2 diabetes, fatty liver disease and cardiovascular disease. In the next few years we may well find that the mechanism by which nutritious foods and exercise improve our health and wellbeing is heavily reliant on these bacterial beauties.
You may have heard of probiotics in foods and supplements. Probiotics are, by definition, bacteria or yeast supplements that must survive digestion and 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, and we are only just beginning to learn which strains help us in what ways. We do know that diversity of bacteria is a good thing.
Pre-biotics, on the other hand, are foods that help your own bacteria by providing the food 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 healthy bacteria. It reduces the diversity of bacteria living in your colon. This kind of eating can create an extra stress on our body, which the immune cells in our gut immediately react to, causing chronic, systemic inflammation. This poor diet can also open the tight junctions between the gut membrane cells, making it easier for pathogens to enter our body, leaving us feeling ill, stressed and miserable. So what to do?
The simplest strategy is to eat more fibre. A higher-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 can’t 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. The accompanying table lists some resistant starch sources that are great food for our gut bacteria to thrive on.
Other pro- and pre-biotic foods include yoghurt containing live or active cultures; fermented foods like 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. Unsurprisingly, 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. 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, or NK, cells. Exercise stimulates and primes the immune system in a healthy way, generally.
However, as I write this, ’tis the season for antibiotics.
Antibiotics kill bacteria. Your gut bacteria are also susceptible to the effects of those antibiotics. If you need to use antibiotics to treat an illness, it could help you to recover by paying attention to your diet in the weeks following that treatment, so that you can build up your protective gut bacteria populations again.
Include lots of vegetables and fruit, plenty of water, and the foods listed in the table above to help your gut, and therefore your immune system, to 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!
- Dr Kirsty Fairbairn is a health, wellness and sports dietitian at Invigorate Nutrition (www.invigoratenutrition.com), based at Eclipse Health, Wellness and Performance, Hanover St, Dunedin.
Food sources of resistant starch to feed good bacteria
Green banana, plantain, pasta salad, inulin, rice salad, sushi, whole grains, wholegrain breads, kumara, legumes (beans, chickpeas, lentils and peas), potato salad, any cold cooked potato, raw oats, taro, cashew nuts and bean salad.