All of us have millions of bacteria living in our gut. These bacteria are very important to our health providing us with protection against infections of the gut, allowing us to gain extra nutritional value from food we eat and helping our immune system. Changes in the balance of these many bacteria can make us vulnerable to infections both from within and from outside the gut. Certain bacteria may also be directly associated with some diseases of the gut. Research by doctors and scientists into relationships between the bacteria normally found in our gut and certain diseases of the gut is helping to develop food supplements and other therapies to treat these diseases.