New research looking at the link between national income, inequality and body size reveals a higher rate of adolescent girls are obese in wealthier countries.

The University of Auckland study, led by Associate Professor Rinki Murphy, looked at 200,000 children in 36 countries including New Zealand, Australia and the UK.

It analysed height and weight data from over 77,000 children aged 6-7 and over 205,000 adolescents aged 13 or 14, from 19 and 36 different countries, respectively.

It discovered obesity rates differed by either the gross national index or the Gini index.

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Young people from countries with a higher gross national index had a higher median BMI compared to children from less wealthy countries.

Adolescent girls from these higher income inequality countries had both a greater median BMI and a less skewed BMI distribution.

Commentary with the research from Professor Murphy acknowledged low nutrition was the likely explanation for seeing greater numbers of underweight children in countries with a lower national income.

However, the prevalence of calorie-dense foods and a decreased necessity for physical activity was likely to be common in both richer and poorer countries.

This could potentially affect young people in both high and low GNI countries, Murphy said.

Other factors could include genes and environmental explanations.

"Differences in the entire BMI distribution of populations from different countries may have biological and environmental explanations, which are important to examine in the context of the economic wealth of the nation and income inequality."

"In wealthier nations increased BMI can be linked to increasing sales of products including food and energy saving devices such as cars and electronic entertainment such as television and video games, which in turn is associated with over consumption of food and increased sedentary behaviour."

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Murphy said more research was needed into why greater income inequality within societies was linked with greater body mass index of adolescent girls.

Further research could also investigate whether BMI distribution of people living in New Zealand differed with gender, socio-economic status or ethnicity.