Obesity link to economic freedom: study
A link exists between a country's economic freedom, fast-food purchases, and obesity, researchers say.
Their results fit New Zealand, among other countries, they said.
The World Health Organisation has used the study as another opportunity to call for governments to take action to "reverse the obesity epidemic by hindering the spread of ultra-processed foodstuffs".
The authors used data on the number of fast-food transactions per capita from 1999 to 2008 in 25 high-income countries and compared that with figures on body mass index (BMI) in the same countries over the same period.
A report of the study, published in the Bulletin of the World Health Organisation, said the work showed that countries adopting market-liberal policies had faster increases in both fast-food consumption and mean BMI.
The average number of fast-food transactions per capita per year increased for all 25 countries in the study, with the 10.1 transactions per capita increase in New Zealand the fourth highest.
Canada (16.6), Australia (14.7) and Ireland (12.3) had larger increases.
According to the OECD, New Zealand has the fourth-highest rate of obesity among members of the organisation, with 27.8 per cent of the population aged 15 and above rated as obese, based on BMI figures.
New Zealand was also ranked fifth in the 2014 index of economic freedom published by US think tank The Heritage Foundation.
The average number of annual fast-food transactions per capita for all countries in the study increased from 26.61 to 32.76, while the average BMI increased from 25.8 to 26.4.
A BMI of 30 or more is considered obese, while one of 25 or more is considered overweight.
The researchers - from the University of California Davis, Queen's University Belfast, and the University of Texas - calculated that each 1-unit increase in the average number of annual fast-food transactions per capita was associated with an increase of 0.0329 in BMI over the study period.
The cause of the link between fast-food purchases and obesity was less clear.
While soft drinks explained a small proportion of it, neither animal fats nor total calories seemed to be significant, the report said.
"This is puzzling. The fat and calories in fast-food meals are usually blamed for the unhealthful effect of fast food.
"Although we cannot exclude the possibility of measurement errors, factors other than calories and fat content may explain why fast food makes people fat," the report said.
"Researchers need to investigate, for example, the metabolic effects of long-term exposure to fast foods produced from the meat of animals fed on corn, kept in confinement and exposed to excessive fertilisation."
More research was also needed to study the effects of the degree of processing of food items and not just their nutrient and caloric content.
The findings had important implications for policy, the researchers said.
"In particular, they suggest that government regulations hindering the spread of fast-food consumption might help to mitigate the obesity epidemic."