Winning the War Inside - Optimising Immunity

Did you know that your immune system is your own personal defence force? 

Often taken for granted, our immune system is an amazingly detailed system of responses working throughout the body to protect us from all kinds of invasions and diseases. Much of it starts in our gut. We are still learning how various (good and bad) bacteria in our gut bolster our defenses against those sneaky germs (pathogens): the viruses and bacteria that make us ill.

Your gut microbiome (which means the community of mainly bacteria present in your gut) forms a barrier to disease-causing pathogens. Each person has a unique ‘signature’ of gut bacteria in our bowel. If we take care of these protective bacteria, they in turn take better care of us!  It’s a symbiotic relationship often overlooked. Emerging research suggests that our gut bacteria influence our appetite through our gut-brain axis, a direct communication line between our gut and brain. This may be how our gut bacteria can impact our chances of being overweight, and developing cancer, type 2 diabetes, fatty liver and cardiovascular disease. In the coming years we will uncover more about how nutritious foods and exercise improve our health and well-being through these little bacterial beauties!

You may have heard of probiotics in foods and supplements. Probiotics are bacteria or yeast products that must survive digestion and the challenging journey through digestion, to be able to set up and live in your gut. There are many different probiotic types, with different strains of bacteria and yeast in them. We are still learning which strains help us in what ways. However, we do know that having lots of different types and kinds of bacteria is a good thing!

Prebiotics are foods that nourish the bacteria already in your gut by providing the nutrients they need to thrive. Some types of carbohydrates are resistant to digestion (called resistant starch), and are used as fuel for our gut bacteria. They then make short chain fatty acids (SCFA) like acetate, proprionate, butyrate and lactate. These SCFAs are absorbed into our blood stream and liver, and positively impact our health.  Butyrate in particular, is highly beneficial.

The typical high-fat, high-sugar, low-fibre Western diet does not promote the growth of healthy bacteria, and reduces the range of different bacteria living in your colon, which is not good. This type of diet can place extra stress on your body that the immune cells in our gut respond to, which can cause inflammation. Additionally, it can compromise your gut lining, making it easier for pathogens to enter the body, leaving you feeling ill, stressed, and miserable! So what can you do? 

The simplest strategy is to eat more fibre. Resistant starch is particularly handy; as mentioned above it's a type of fibre our gut bacteria love. Table 1 lists some resistant starch food sources. 

Table 1: Food sources of Resistant Starch to feed that good bacteria!

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.

Emerging research highlights the connection between exercise and gut health. Regular moderate exercise or high-intensity interval training can increase the range of different gut bacteria; most beneficial when started young. While intense exercise can temporarily stress the gut, the overall long-term impact is positive. Exercise also encourages positive movement of immune cells from the lymph into the blood and out to tissues, helping us adapt to the exercise stress better. This includes the brilliantly named natural killer cells, or NK cells; who wouldn’t want those on their side? In general, exercise primes the immune system in a healthy way.

However, as I write this, ‘tis the season for illness, often treated with antibiotics Antibiotics, by definition, kill bacteria.  Your gut bacteria are also vulnerable to antibiotics. If you need to use antibiotics to treat your illness, paying attention to your diet in the weeks following treatment can help rebuild your protective gut bacteria population. Include plenty of vegetables and fruit, drink lots of water, and eat some of the foods listed in Table 1 to support your gut and immune system recovery.

Fortunately, winter is also a season where many of us eat more legumes, which are a fantastic source of fibre and resistant starch. Add legumes like beans, lentils, peas (including split peas) and chickpeas to your soups and casseroles – your body will thank you for it!