Fibre and phytochemicals for gut health and immunity
Eating a wide variety of plant foods encourages different types of good bacteria to thrive in the gut. “I recommend 30 different types of plants a week”, says Tim Spector, Professor of Genetic Epidemiology and lead on the Covid-19 Zoe symptom study app. “A healthy gut microbiome is crucial to a healthy immune system”, he continues. Most of the body’s immune cells are in the lining of the intestine, and microbes in the gut play a crucial role in keeping this system healthy.
Plant-based diets are typically higher in fibre, a key nutrient needed for a healthy gut microbiome. For example, gut bacteria ferments, or “feeds on”, fibre and creates short-chain fatty acids, which have been shown to improve immunity against pathogens.
It’s important to eat the recommended 30g fibre per day, but adults eat an average of 18g. Foods high in fibre include many fruits such as berries, pears and oranges, vegetables such as broccoli, carrots and sweetcorn, brown pasta, brown rice, wholegrain bread, beans, lentils, chickpeas and nuts.
Phytochemicals, compounds produced by plants including fruits, vegetables, grains and beans, are also believed to increase some types of beneficial gut bacteria. The colour of a plant is determined by the phytochemicals it contains, and some of these are associated with “positive benefits for the immune system”, says dietitian Sophie Medlin. The wider the variety of different coloured plants you eat, the more types of phytochemicals you’ll consume. Red, orange, yellow and green plants contain carotenoids, which have been associated with boosting immunity. Although evidence for the benefits of phytochemicals to immunity is not conclusive, there is no health downside to eating five a day.
Eating for a healthy gut is a long-term approach. While modifying your diet can positively impact your gut bacteria and immune parameters within three months, research finds the alterations do not “reflect the degree of change that occur with a long-term vegetarian diet”.