What is making Kiwis fatter?

Overeating to gain weight is not usually a conscious individual decision and many aspects of the food environment influence our diet. Photo / 123RF

An over-supply of high-energy, high-calorie foods in many countries has been today shown by New Zealand researchers as a likely driver of rising global obesity.

An Auckland University-led study, published today in the Bulletin of the World Health Organization, analysed increases in food energy supply and obesity in 69 countries.

It found that both body weight and food energy supply had increased in 56 (81 per cent) of the countries surveyed between 1971 and 2010, while in 45 (65 per cent) countries, which were mostly high-income countries like New Zealand, the increase in food energy supply was more than enough to explain the increases in average body weight.

"Our study shows that oversupply of calories is a likely driver of over-consumption of those calories and can readily explain the weight gain seen in most countries," said lead author Dr Stefanie Vandevijvere, of the university's School of Population Health.

"Overeating to gain weight is not usually a conscious individual decision and many aspects of the food environment influence our diet. One of these is likely to be the sheer quantity of palatable, ultra-processed food products available in the food supply," she said.

"It creates a kind of push effect on our diet and we tend to subconsciously overeat on the calories and gain weight."

Dr Vandevijvere said the study was important because it provided more evidence that governments need to develop the right policies to reduce obesity, which was a risk factor for many health problems, including diabetes, heart disease, stroke and some cancers.

In New Zealand, poor nutrition and obesity combined has accounted for 11 per cent of health loss - or death and disability - a rate greater than that attributable to tobacco.

Our rate of obesity, putting us high in OECD rankings, has more than doubled in the past 20 years and recent figures showed 31 per cent of Kiwi adults and 11 per cent of children were now considered obese.

We haven't been alone.

Between 1980 and 2013, the proportion of adults globally who were overweight, increased from 28.8 per cent to 36.9 per cent in men, and from 29.8 per cent to 38 per cent in women.

In 2013, the 194 member states of the World Health Organisation (WHO) agreed on a global action plan that included a voluntary target of halting the rise in diabetes and obesity.

It also proposed measures that countries can take to tackle obesity, including restriction of the marketing of unhealthy foods to children, food pricing strategies such as taxes on unhealthy foods, and improving the nutritional quality of foods in schools and other public sector settings.

In their study, Dr Vandevijvere and her colleagues compared data on food energy supply and average adult body weight in the 69 countries from the United Nations Food and Agriculture Organization (FAO) database and several databases on average adult weight, including the WHO global database on BMI, from two periods of time between 1971 and 2010.

The FAO estimated the food supply of countries by balancing local production, country-wide stocks and imports with their exports, agricultural use for livestock, seed and some components of waste.

Waste on the farm, during distribution and processing, as well as losses due to transformation of primary commodities into processed products, were usually taken into account, but not losses of edible food, such as domestic animal feed, plate-waste and other food that is thrown away.

Dr Vandevijvere said the amount of added energy intake needed to gain weight was surprisingly small.

Just 100 kJ of energy was about a half a plain biscuit or a mouthful of soft drink, yet if that energy intake was sustained, it would result in an extra kilogram in weight.

Some of the countries in the study had much larger increases in food energy supply than could be explained by the average increase in weight of the population, she said.

"This suggests that an increasing amount of food is wasted and there is some evidence to support that this is the case."