There is a direct link between the amount of green space in England's major cities and how many citizens suffer diabetes and obesity, according to a new report.
A lack of green space and a high percentage of housing means people in cities such as Birmingham, London, Newcastle and Liverpool are more likely to suffer ill health.
The report, from the Royal Institute of British Architects (RIBA), calls for urgent action to save the UK £1 billion a year by opening up green spaces and creating more places for people to walk.
It said the NHS alone could save £675 million every year if action was taken to create "healthier cities".
The review looked at the nine most populated cities in England - Birmingham, Bristol, Leeds, Liverpool, London, Manchester, Newcastle, Nottingham and Sheffield.
Researchers found that the healthiest local authorities in major cities had almost half the housing density and a fifth more green space than the least healthy ones.
The total percentage of green space in the five worst performing local authorities outside London was 51.2%, and the percentage of land occupied by housing was 6.1%.
In contrast, the five best performing local authorities outside London were 73.2% green space and only 3% housing.
Birmingham and Liverpool were the worst cities for health, with Birmingham having the least active adults and the highest number of adults with diabetes, and Liverpool having the most obese children.
Parts of London and Newcastle also had low numbers of active adults.
Looking at diabetes overall, the least healthy areas in England's cities had twice the housing density and a quarter less green space than the most healthy areas.
Meanwhile for childhood obesity, green space was 44.7% in the worst cities while the percentage of land occupied by housing was 6.8%.
In comparison, the five local authorities outside London with the lowest rates of childhood obesity were 71.4% green space a nd only 3.1% housing.
Adults in Leeds were the most active out of the nine largest English cities, while Bristol had the lowest number of adults with diabetes and obese children.
A poll of 1,300 people from across the nine cities found that 59% were meeting the recommended 150 minutes per week of exercise. But 75% of people who did not do enough exercise said they could be convinced to walk more each week. A quarter said nothing could change their decision not to walk.
Department for Transport data show that walking has dropped 27% in the last 15 years.
RIBA president Stephen Hodder said: "At a time of austerity and increased concern with physical and mental wellbeing, it's shocking to discover that just by making public health a priority when planning cities, we can save the country upwards of £1bn annually though reduced obesity-related healthcare costs.
"With responsibility for public healthcare devolved now from central Government to local authorities, it's vital that planners and developers take the lead and ensure healthier cities."