Children are said to be one thing about nutrition and health at school, and something very different on home travel, the NSW Cancer Council has revealed.
The new study found that 82% of food advertising on Sydney buses and railway stations is for undesirable foods, despite rising childhood obesity rates.
"This is extremely worrying, as 21.4% of NSW children aged 5-16 years are now overweight or obese," said Wendy Watson, director of NSW's Children's Nutrition Program.
"If they bear that weight in adulthood, it puts them at risk 12 different cancers, as well as heart disease and type 2 diabetes."
The NSW government has several initiatives to educate children on healthy eating from pre-school to adulthood.
Public transport ads run counter to this message and target audiences are often children.
Every month, children under the age of 15 in NSW make more than 3.3 million bus journeys and over 2 million train trips.
"Only 12% of food advertisements that children see when they are out and are for a healthy diet. This undermines parents' efforts to create healthy habits."
NSW Cancer Council wants the government to remove junk advertising from public transport.
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It is not unprecedented.
The ACT government has done it on buses, and in Western Australia advertising for spirits has been banned in all public transport.
"Obesity in childhood is today a priority of the prime minister. If we want to see a real fall in overweight and obesity, this is a way the New South Wales government can show leadership, "said Watson.