Your gut and immunity
You’ve probably heard the statistic that around 70% of your body’s immune cells are located in and around your gut. It makes sense that so much of your immune system is concentrated here - your gut is continually exposed to a vast amount of microbes and antigens (substances that can trigger an immune response) from food and the outside environment.
It’s the job of the immune cells which line your gut to keep an eye on what’s passing through and decide what’s friend or foe. Your gut microbes are key to this process: they train your immune cells to respond appropriately and prevent them mounting an attack against harmless microbes and food.
Microbial messengers
One of the ways your gut microbes communicate with your immune system is through the production of metabolites - small compounds they make when they convert food into energy. For example, when your microbes break down fibre, they produce short chain fatty acids (or SCFAs). SCFAs play an important role in keeping your gut lining healthy. But they also interact with the immune cells in your gut lining and can influence immune responses.
Take butyrate - one of the primary SCFAs your microbes produce. Butyrate influences the number and effectiveness of TRegs (regulatory T cells). TRegs are a type of white blood cell that help regulate inflammation. They also promote tolerance by ensuring your body doesn’t attack its own tissues. In short, they help prevent an overactive immune system.
SCFAs also encourage the cells lining your gut to make the protective mucus which acts as the first line of defence against pathogens and foodborne toxins.
What’s the evidence?
Your immune system is incredibly complex, which makes measuring the impact of diet (or other lifestyle factors) on its function very challenging. However, experimental models (which scientists use to build hypotheses that can then be tested) support the idea that fibre plays an important role in immune health.
For example, in mouse studies, a lack of fibre has been shown to disrupt the gut barrier, increasing susceptibility to infection. In contrast mice fed a diet high in fermentable fibre had increased levels of SCFAs and a lower risk of allergic inflammation.
Scientists are now interested in whether high fibre diets - or specific fibres - might be useful for regulating immune function in humans.
If fibre was a playlist, we’d be on repeat
Fibre is important for the health of our gut microbiome, which in turn plays a role in immune function. So far, so good. But as you’ve probably heard, most of us aren’t eating the recommended 30 grams of fibre a day.
I’ve shared lots of advice on upping your fibre intake (you can read more here and here!) - but this time, choose one low fibre meal or snack to upgrade and focus on this for a few weeks. For example:
- Lunch a grab-and-go sandwich on white? Swap for a packed lunch of pesto pasta salad (cold pasta is high in gut-bug-loving resistant starch).
- Dinner where you fall down? Get into the habit of eating a veggie starter or add a side of peas to boost your total intake.
- Snacks a fibre weak spot? Swap a bag of crisps for popcorn or try dark chocolate with a handful of nuts.
These small swaps add up quickly and are easier to stick with than overhauling your whole diet at once. If you need some more inspiration, here are seven high fibre foods to add to your grocery list:
- Oats - ½ cup = 5g fibre. This time of year it’s gotta be porridge or baked oats.
- Chia seeds - 1 tbsp = 5g fibre. Add to porridge, muesli, or a seed mix.
- Peas - 3 heaped tbsp = 5g fibre. Defrost and throw into a salad, smash with mint and olive oil and serve over toast with a boiled egg, add to a pasta salad, or toss into a risotto at the end of cooking.
- Raspberries - 3 heaped tbsp = 6g fibre. A great snack with a side of yoghurt and a seedy topping or smoosh over tahini or PB on toast for a high-fibre alternative to jam. Add a drizzle of honey if you like.
- Chickpeas - ½ can = 7g fibre. Add to a salad, curry, or soup - or make a chickpea coronation sandwich by mixing chickpeas with mayo, mango chutney, curry powder, red onion, and chopped coriander for a high-fibre take on a classic.
- Kiwi fruit - 2 kiwis = 6g fibre. Chop and scatter over your breakfast or pack as a snack. A great low FODMAP option too.
- Dried apricots – 3 apricots = 3g fibre. Perfect to stash in your bag with a handful of nuts, chop over porridge or yoghurt, or dip in melted dark chocolate and set for a sweet after-dinner treat.
Lastly, here are five fibre-rich recipes to add to your meal plan this autumn:
- Chickpea curry with bulgar wheat
- Power porridge with oats and pear compote
- Smoky three bean chilli -
- Roasted carrot and parsnip soup - serve with rye or seedy bread for extra fibre points
- Lamb and lentil meatballs - choose wholemeal flatbreads
In summary
Your immune system is incredibly complex, and there’s no single strategy that will protect you from every illness. But alongside exercise, good sleep, and stress management, a healthy, high-fibre diet is another strategy you can employ to support your immune health.
Sources
Short chain fatty acids: key regulators of the local and systemic immune response in inflammatory diseases and infections. In Open Biology. Royal Society Publishing. (2023). Link.
Role of dietary fiber in promoting immune health—An EAACI position paper. Allergy: European Journal of Allergy and Clinical Immunology. (2022). Link.
