Professor Bob Rastall: The range of functional food products coming onto the market, such as those containing pre- and probiotics, continues to increase. They are designed to have a positive effect on health and, on the principle that prevention of disease is better than cure, this approach clearly has a role to play in promoting long and healthy lives, particularly in a society with an increasing life expectancy. But how much do these products really contribute to good health? Professor Rastall will explain the science behind functional foods and consider to what extent the claims made by the manufacturers are supported by the underlying science.