Supporting your immune system with a plant-based diet

The immune system is critical to all aspects of our health. Although we think about good immunity in relation to our ability to fight infection, a healthy immune system is actually crucial for the prevention of most chronic illnesses. For example, if our immune system is overactive this can give rise to autoimmune diseases and if it is not functioning adequately, it can allow cancer cells to grow unregulated. In fact, most chronic diseases are triggered in some way by low level chronic inflammation which then has a knock-on adverse effect on the immune system (1). 

It turns out that 70% of our immune system actually resides in our gut. It’s pretty incredible to think that the trillions of bacteria and other organisms in the gut play such an important role (2). We know the most about the bacteria in the large intestine and these bacteria are involved in regulating and educating the immune system. When provided with the right food, the good bacteria can flourish and are able to make compounds such as short chain fatty acids that are essential to the functioning of the immune system. These signalling molecules can activate cells of the immune system and can communicate with other organs such as the brain and lungs thus regulating their immune systems too. In addition, the gut bacteria are involved in making vitamins and hormones that are required for good health.

There are a number of factors that impact the health of our gut microbiome and our immune system in general. Some we have control over and other we don’t. For example, getting older generally results in a decline in the functioning of the immune system (3). Other factors that adversely affect the immune system are being an unhealthy weight, an unhealthy diet, poor sleep, lack of exercise, certain prescribed medications such as antibiotics, stress, tobacco smoking and alcohol (4).

The only foods you need in the diet to maintain your immune system are healthy plant foods. One crucial nutrient required to support the growth of healthy gut bacteria is fibre. Fibre is a type of carbohydrate that is not fully digested by the body and makes its way down to the large bowel and is used as fuel by the resident bacteria. Fibre is only found in plant foods. Adults should be aiming to consume at least 30g of fibre a day (5). 

Another important aspect is eating a variety of plant foods. The American Gut Project has shown that those participants consuming at least 30 different plant foods a week have the most diversity of gut bacteria, which is associated with better health (6). 

Plant foods are rich in micronutrients, vitamins and minerals, that are required for a healthy immune system. These are listed in the table below. It’s important to incorporate a wide range of colourful fruits and vegetables every day, eat plenty of beans and whole grains, be liberal in your use of herbs and spices, make sure you are getting enough vitamin D and drink mainly water for thirst, although if you enjoy tea and coffee these drinks can also have benefits for the immune system. Some particular superstars amongst plant-based foods are mushrooms and nutritional yeast, high in beta-glucans, cruciferous vegetables such as broccoli, kale and cabbage, turmeric, flavonoids, such as quercetin found in brightly coloured fruits and vegetables and of course vitamin C (7,8).

Prebiotics are food for your gut bacteria. They are generally foods that are high in non-digestible fibre such as whole grains, bananas, greens, onions, garlic, soya beans and artichokes. Probiotics are foods that contain live bacteria or yeast, usually because they have been fermented. This includes foods such as sauerkraut, kimchi, tempeh, miso, water kefir and kombucha. Some plant-based yogurts now also contain live cultures. Most people in good health do not benefit from taking a probiotic supplement.

A healthy plant-based diet is a great start for supporting your immune system. Other lifestyle habits are also really important. These include regular physical activity of at least 150 minutes per week, 7-9 hours of regular, restorative sleep, minimising stress and avoiding tobacco smoking and alcohol.

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