Build better immunity: The secret weapon of a healthy gut

Dietitian Katrina Pace looks at the role our gut bacteria play in helping us fight off infection.

The word immune means free or untouched. And that’s exactly the role of our immune system, to keep us free from things that may harm us. A healthy immune system is essential in helping resist a cold, fight off chicken pox or defend against a host of other infections.

The immune system at work

Our immune system is a network of cells, tissues and organs that work together to keep out pathogens. Pathogens are anything foreign to the body that may harm it – that might be dust, pollen, a splinter, a virus, bacteria or other harmful substances.

Our bodies have layers of defence to protect them from pathogens. Our skin is one layer of our immune system, a physical barrier keeping out pathogens. If we cut our skin, bacteria may get through and cause an infection. The mucous layer that coats the inside of our nose and digestive system is another barrier, and in our blood stream, white blood cells gobble up harmful cells, and ‘remember’ what they were, so next time they know what and how to attack. Other cells in our blood or tissues neutralise pathogens or signal to other cells that a particular pathogen needs to be destroyed.

The gut’s important role

The gut is one of the places where the immune system meets lots of foreign objects. Not just food and nutrients (and some non-food items), but bacteria, viruses, fungi and parasites. So, it may be no surprise the gut is one of the main places where your immune system resides. There are many cells in the gut that work to release immune factors affecting the whole body, and others that function only to protect the lining of the gut.

Bacteria at work

Gut bacteria are integral to the immune work the gut undertakes. We now know gut bacteria are essential to our immune system working properly. Our intestines are the largest single immune organ in our body.

Certain bacteria, or the nutritional components they produce, have been shown to interact with immune cells and affect how immune systems work.

Short-chain fatty acids (SCFA) are some of the nutritional components produced by certain bacteria as they ferment indigestible fibres. One of the roles of SCFA is to reduce inflammation, which helps protect our gut lining and makes sure the gut immune cells can produce the right immune factors and prevent infections.

Certain bacteria can reduce the effectiveness of digestive enzymes that are released from cells that line the gut. Bacteria also help keep the gut lining healthy and gut barrier function working properly.

A breach of the barrier

‘Leaky gut’ is the layperson’s term given to increased permeability of the gut lining, through a reduction in the mucous layer and increased gaps between cells that line the gut. Leaky gut is thought to allow bacteria and other nutrients through to the bloodstream, where they shouldn’t be. This may trigger increased inflammation and immune response. The results of a leaky gut can be one of the causes behind autoimmune diseases such as IBD, coeliac disease, allergies, asthma and type 1 diabetes. A healthy gut is crucial in protecting against autoimmune diseases, which we now know can be triggered by bacterial toxins or viruses passing through the gut wall.

Nine ways to boost your immune system by growing great bacteria

1. Try fermented foods

Fermented foods are an easy way to increase the beneficial bacteria in our gut. Kombucha, kefir, sauerkraut, kimchi and yoghurt have all been shown to contain bacteria and yeasts that can help reduce inflammation and improve gut bacteria growth. Start off with a small amount, 1-2 tablespoons daily, and increase over time. If you are pregnant please see our advice on fermented foods and pregnancy.

2. Eat more fibre

Gut bacteria digest certain fibres to produce short-chain fatty acids (SCFA), which reduce inflammation and can affect how the immune system works by changing immune cells. Acetate, the main SCFA produced by gut bacteria after digesting the fibre found in fruit, vegetables, nuts and grains, reduces gut permeability (leaky gut). Butyrate, another SCFA, reduces inflammation, improves the movement of food through the gut and may help protect against colon cancer.

3. Choose your alcohol carefully

Alcohol can increase the growth of certain bacteria that potentially cause an increase in toxins in the gut. Alcohol can also increase leaky gut and inflammation. Spirits may do more gut damage than wine or beer, and the amount and frequency of alcohol intake definitely plays a part in the amount of gut damage seen.

4. Manage stress

Not only does stress influence your gut bacteria, growing more of certain types of bacteria has also been linked to higher risk of experiencing anxiety and depression. Managing your stress can be one step towards improving your gut health and immunity. Although no studies have yet looked at the impact of stress management on changes in gut bacteria growth, yoga has been shown to be as effective as a low-FODMAP diet on the symptoms of irritable bowel syndrome.

5. Mind that fat

A high-fat Western-style diet reduces a bacterium called Akkermansia muciniphila, which plays a part in reducing inflammation through changes to immune cells. In mice, who have a very similar gut bacteria profile to humans, a high-fat diet has also been implicated in leaky gut.

6. Subtract some additives

Emulsifiers are additives mixed with certain foods to stabilise them. Usually they’re added to keep two liquids, that don’t usually mix, together, for example combining vinegar and eggs with oil to make mayonnaise. Lecithin, which is naturally present in egg yolk, helps keep the vinegar and oil together. Sometimes chemicals are used as emulsifiers, and indications are that these types of emulsifiers can increase the permeability of the gut lining. Choosing whole foods and avoiding packet foods as much as possible will help to reduce your intake of emulsifiers.

7. Make omega-3 a regular

Regular omega-3 fats from fish have been shown to be great for our gut bacteria and, as an anti-inflammatory, are well known to help prevent heart disease and ease the pain of arthritis. Now it seems omega-3s also work to reduce inflammation in the gut by encouraging or discouraging growth of certain bacteria.

8. Use coffee wisely

Coffee contains caffeine, which has been shown in both human and animal studies to change gut microbiota. Coffee contains naturally occurring soluble fibre and phenolic compounds that are food for gut bacteria. One study, which investigated the effect of three cups of coffee a day on gut bacteria, found this increased the amount of bifidobacteria, especially in people who were growing low numbers. Bifidobacteria are particularly useful in making sure you’ve got a healthy immune system.

9. Artificial sweeteners

Artificial sweeteners, such as mannitol and sorbitol, are known to change gut bacteria. In fact, in the low-FODMAP diet, these sweeteners are in the ‘polyol’ group and can cause symptoms in people sensitive to them. Look carefully at ‘sugar-free’ products. If they contain one of these sweeteners, there may also be a warning that too much of that food may act as a laxative. Although research in both humans and animals shows that different artificial sweeteners can affect the gut microbiota by reducing bacterial diversity and encouraging overgrowth of certain types of unfavourable bacteria, artificial sweeteners are only one part of the Western diet profile that may contribute to changes. It’s very hard to see how big a role artificial sweeteners actually play, compared with other dietary factors.

Eat your way to better immunity

A great way to boost your immunity, coming into winter, is to make sure you’re packing your diet full of fibre (from whole grains, fruit, vegetables, beans and pulses) and omega-3 fats, as well as trying to eat homemade where possible. See our high-fibre recipes for more inspiration.

• Breakfast: Wholegrain oat porridge (fibre) and banana (resistant starch), topped with a spoonful of probiotic yoghurt
• Lunch: Seeded sourdough bread (fibre), canned red salmon (omega-3), salad of lettuce, cucumber, tomato, red onion, olives, orange capsicum (fibre) with 1/2 cup mixed beans (fibre) and 1 tablespoon kimchi or sauerkraut (good bacteria)
• Evening meal: Vege and lentil curry with coconut rice (fibre)
• Snacks: Mixed nuts and raisins or homemade hummus with vege sticks