There are calls for tighter restrictions on junk food advertising. Credit:Andrew Quilty More than 40 per cent of children in the area had a body mass index over the healthy range and half were obese, according to the most recent data. Just over one third of children in the PHA covering Mount Druitt and Whalan were obese or overweight, closely followed by Canley Vale, Ashcroft, Lakemba, Punchbowl and Liverpool. Mosman – one of the city's richest postcodes – had the lowest rate of overweight and obese children (17 per cent). Sydney's other ultra-rich suburbs follow suit. Fewer than one in five children had BMIs above the healthy range in the PHAs encompassing Killara, Cremorne, Kirribilli, Double Bay, North Sydney, Balmain, Avalon and Palm Beach.

Maroubra, La Perouse and Chifley were the only coastal Sydney suburbs where more than one in four children were obese. "We are a remarkably overweight population, and we are seeing it more and more in our children," said Professor Rosemary Calder, public health expert and director of the Australian Health Policy Collaboration (AHPC), which produces the Health Tracker. "For obesity to be at such high levels among this young group, something is going very wrong," she said. Childhood obesity is a powerful risk factor for cardiovascular disease, diabetes, respiratory conditions, cancer and depression, Professor Calder said. "This is a generation that our health system is going to have to manage," she said.

Highest rates of obese and overweight children 1. Homebush Bay and Silverwater

2. Mount Druitt and Whalan

3. Canley Vale, Canley Heights and Fairfield

4. Ashcroft

5. Lakemba, Wiley Park/Punchbowl Lowest rates of obese and overweight children 1. Mosman

2. Gordon, Killara and Pymble

3. Double Bay Cremorne, Cammeray, Neutral Bay and Kirribilli

4. North Sydney

5. Avalon, Palm Beach, Newport and Bilgola

Where the sedentary live The highest rate of adults who do no or little exercise follows an almost identical route through Sydney's west. Cabramatta was Sydney's least active suburb, with almost 80 per cent of people doing no or very low amounts of exercise (walking less than three hours a week). Another 14 PHAs – all in western Sydney – reported over 75 per cent of adults did no or little exercise. The most active PHAs were again some of Sydney's most affluent suburbs: Double Bay (44.4 per cent did no or little exercise), Dover Heights, Rose Bay and Vaucluse (50.4 per cent), Bondi Beach (51.6 per cent) and the inner city and north-east (52.1 per cent).

Least active Sydney areas 1. Cabramatta and Lansvale

2. Canley Vale, Canley Heights

3. Fairfield

4. Mount Druitt

5. Blacktown Most active Sydney areas 1. Double Bay

2. Dover Heights, Rose Bay and Vaucluse

3. Bondi Beach

4. Inner city and north-east

5. Cremorne Cammeray, Kirribilli and Neutral Bay

Deaths due to cancer, cardiovascular disease, respiratory disease and diabetes, as well as adult obesity, follow the same geographical pattern of health disparity across Sydney. It's a trend largely dependent on the wealth of communities, Professor Calder said. "We often hear 'people make choices', that they can choose to be healthy. That's completely fallacious. Your environment influences your choices. "Those choices are obscured when you live in a community where fast-food outlets and alcohol stores are pervasive much more so than parks and walking tracks. "It's not surprising that healthy activity and healthy diets track with healthier suburbs," she said, pointing to a more enticing outdoor environment that encourages people to be active.

Suburbs closer to the CBD have more connected public transport that supports incidental exercise, and healthier food options, whereas many western Sydney residents sit in their cars for hours a day coming to and from work. "They may not have the resources for a bicycle or live in an area where it's not very safe for children to ride to school because of the distance, busy roads, or industrial areas," she said. In 2016 the AHPC's Getting Australia's Health on Track report outlined 10 priority policy actions to prevent and reduce chronic diseases in Australia, including a sugar tax, restrictions on junk food advertising to children and national initiatives to increase the rates of walking and cycling to school and work. "We don't regard health as a national asset. It's used as a political football, and it can be a huge national burden if we don't get it right," Professor Calder said.