Public health advocates warn the nation's 12.5 million population of adults over a healthy weight will balloon further if action is not taken.

The Australian Bureau of Statistics' national health survey data shows that the number of overweight or obese young adults hit 1 million in 2017-18, or 46 per cent of those aged 18-to-24.

It marks an 18 per cent increase in the number of young adults over a healthy weight in just three years; in 2014-15, the figure was 39 per cent of 18-to-24-year-olds. Within the group, 30.3 per cent had a body mass index of between 25 and 29.99, making them medically overweight, while 15.5 per cent were obese - meaning a BMI of 30 or above.

The Australian Medical Association and Obesity Coalition renewed calls for the federal government - which is working on a National Obesity Strategy with the states and territories - to introduce a tax on sugary drinks, mandate health star ratings and crack down on junk food advertising.

Obesity Coalition executive manager Jane Martin said the fact Australians were exceeding the healthy weight range at a younger age was concerning, as many would continue to gain weight as they aged. This put them at increased risk of chronic health conditions such as type 2 diabetes, heart disease and stroke, she warned.

"It's a concern for having a healthy and productive workforce, but it's also concerning for the strain that it's going to put on our hospital system," Ms Martin said.

"What you can see is this big kick-up in late adolescence of weight, a huge amount of weight gain happening - particularly in boys - between late high school and early adulthood ... We know the processed food industry is targeting that cohort."

She noted that UberEats reported its top-selling item in 2018, for the second year running, was hot chips.

"This is a point of young people's lives where they are at risk of becoming an unhealthy weight and we really do need to do more."

AMA president Tony Bartone said the "significant" increase in young people over a healthy weight should come as a warning to policy makers.

"We really do need to look at all the levers that we can pull to get this under control," Dr Bartone said.

The ABS data showed the proportion of obese adults rose from 28 per cent in 2014-15 to 31 per cent in 2017-18, driving up the overall adult overweight or obese population to 12.5 million people - two-thirds or 67 per cent of all adults, up from 63 per cent.

Dr Bartone said the AMA and public health experts were united in advocating a tax on sugary drinks, with the revenue to be poured into the health system "to help treat the epidemic" - and a ban on advertising junk food to children, including on social media and in sport.

"You've got to start at an early age in changing behaviours, because once you get to teenagers you've missed the boat."

Dr Bartone said the fact that only 1.9 per cent of 15-to-17-year-olds met national guidelines for physical activity, also revealed in the ABS data, was "an absolute disgrace" in "a country that has such a proud sports-loving tradition".

The ABS data showed 9 per cent of adults and 7 per cent of children consume sugary drinks every day, while only 5 per cent of adults and 6 per cent of children ate the recommended amount of fruit and vegetables.

Youth and Sport Minister Richard Colbeck said "the government supports a range of healthy eating campaigns to help promote healthier choices and lifestyles, including the Health Star Rating system, Healthy Food Partnership and the Australian Dietary Guidelines".

He said a review of nutrition labelling for added sugars was recently commissioned and noted that "limiting sugar intake is considered just one part of a healthy diet".

"The Australian Government does not support a sugar tax," he said.

A National Obesity Strategy is expected to be presented to the COAG Health Council in June 2020.