More than half of our immune system is found in the digestive tract. That's why what we eat affects our health straight away.

An entire ecosystem of bacteria lives there, doing everything from turning food into vitamins to regulating our hormones. What we need to maintain this system active is probiotic and prebiotic elements in our diet.

Probiotics are foods that promote the growth of the so-called friendly bacteria. Among the most important are Lactobacillus acidophilus and bifidus, found in yoghurt (with live bacteria), kefir (a fermented milk drink), tempeh (a soy product), miso or sauerkraut.

To ensure these beneficial bacteria thrive, we also need to feed them prebiotic foods, non-digestible food fibres that help good bacteria stick to the bowel wall and stimulate their growth. Foods rich in prebiotics are bananas, soybeans, artichokes, whole oats, wheat, barley, garlic, legumes, tomatoes and green vegetables.

Combine probiotic and prebiotic foods and you'll have the best results if you want to boost your immune system.