The Prince of Wales has urged more people to walk and cycle in a bid to tackle unhealthy living.
Prince Charles frequently discusses his views on modern architecture
He raised concerns Britain was closely following the US in the consumption of fast food and lack of exercise.
Speaking to a conference in London on design and health, he said: "We are perhaps not far behind our American cousins in the 'supersizing' epidemic."
Charles blamed the infrastructure of towns and cities for discouraging pedestrians and physical activity.
The prince questioned the role town planning had in promoting people's health.
"Research... suggests that walking or cycling for just half an hour a day can have a significant improvement on our state of health.
"But why don't we do it more?"
Town planning challenge
Referring to research by fellow speaker Dr Richard Jackson, the prince said it was often "because our towns and cities make it nearly impossible, and because it might help if the built environment was more attractive and appealing to the pedestrian".
Dr Jackson, professor at the University of California School of Health, also addressed the conference organised by the Prince's Foundation for the Built Environment and the King's Fund.
He has linked obesity and mental illness directly with poorly designed neighbourhoods and wants British town planners to make cities healthier for people.
Prince Charles said: "Dr Jackson and his colleagues have pointed to a disturbing link between the built environment, physical inactivity and what he terms a 'syndemic' of diseases including, perhaps most worryingly, childhood obesity."