Emaciated children have long been the enduring image synonymous with poor nutrition in developing countries, while obesity was considered the curse of rich nations.

But a study published in The Lancet on Wednesday shows this dynamic is shifting.

Obesity rates among five to 19-year-olds rose tenfold in the past four decades, from 11 million in 1975 to 124 million in 2016.

Proportionally, 0.7 per cent of children were obese in 1975, compared to 5.6 per cent of girls and 7.8 per cent of boys in 2016, found the researchers at imperial College London and the World Health Organisation. One in five children is now obese or overweight.

If the trend continues, more children and adolescents will be obese than moderately to severely underweight by 2022, according to the analysis of the weight and height measurements of nearly 130 million people - the largest ever epidemiological study, according to WHO.

Emaciation and growth stunting were still significant, and critical issues, especially in war-torn, famine-hit regions. But obesity is increasingly being linked to malnutrition in poor communities whose food supply is limited to high-processed food of little nutritional value.

Obesity rates continue to soar globally in low to middle-income countries, but have started to plateau in higher income states, though at unacceptably high levels, said lead author Professor Majid Ezzati at Imperial College's School of Public Health.

The findings "highlight the disconnect between the global dialogue on overweight and obesity, which has largely overlooked the remaining under-nutrition burden.

"Initiatives focusing on under-nutrition have paid little attention to the looming burden of overweight and obesity," the authors wrote.

Professor Ezzati said the "worrying trends reflect the impact of food marketing and policies across the globe, with healthy nutritious foods too expensive for poor families and communities" and "foreshadowed a generation of children and adolescents will grow up obese and at greater risk of metabolic diseases, like diabetes and heart disease".

"We need ways to make healthy, nutritious food more available at home and school, especially in poor families and communities, and regulations and taxes to protect children from unhealthy foods," he said.

In Brisbane this week, WHO delegates at the Western Pacific Committee meeting are developing a regional action plan to protect children from the harmful impact of food marketing.

The region is home to the countries with the largest proportion of obese children.

The rise in obesity was not the result of a lack of resolve among individuals to eat healthy foods, said Dr Francesco Branca, director of nutrition for health and development.

Environmental factors not only persuade but in many cases dictate what people eat.

"We need to give the opportunity to give people the right food at the right time and right price and we need to allow them to make choices without the distortions that inappropriate marketing can give," Dr Branca said.

Obesity rates were also going up among children under five years old, sitting at roughly 7 per cent globally, he said.

"If you want to prevent obesity you have to start early."

Part of the solution was ensuring healthy foods were available in schools, hospitals and public canteens.

"That would be an incredible leverage power for the government," he said.

The Chilean government has introduced a simple labelling system indicating when foods have unhealthy levels of sugar or fat.

"Children themselves see the black label and think, 'oh wow this food is not good for us', kindergarten aged children."

Every Australian state and territory has implemented nutrition policies for school canteens, including a ban on sugary drinks in NSW tuckshops.

In June, the NSW government announced sugary drinks would be removed from the menu at all NSW hospitals and health facilities under a range of measures to combat obesity.

The Alfred hospital in Melbourne reduced sugary drink sales by 36,500 a year by removing them from display at its main service cafe and placing them under the counter in 2010, while overall drinks sales have remained steady.

In Victoria's south-west, 13 health districts have discontinued the sale of sugary drinks at their hospitals and facilities.