An imbalanced diet is the primary cause of the majority of non-communicable diseases. In particular, obesity rates are increasing in both the developed and developing world and this disease has been described as a pandemic by the World Health Organization. Many governments provide dietary guidelines, for example, recommended weekly amounts of different food types, but the increasing incidence of obesity shows that these campaigns have not been successful. We developed a mobile app that shows supermarket shoppers the nutritional balance of their shopping trolley. A twomonth study demonstrated that the app led to significant changes in participants' shopping habits and an improvement the nutritional balance of their diets.