Extra calories not lack of exercise causing obesity

The researchers from Auckland University of Technology (AUT) also say nutritious food is more expensive, rates of obesity are higher in those who are poorer and physical activity can not fully compensate for consuming too many calories.

Professor of Nutrition Elaine Rush, is the co-author of the study which examined the relationship between ‘energy in' and ‘energy out', using measurements made in New Zealand, the U.S. and the Netherlands and she says there is no evidence that a considerable reduction in physical activity has been a contributor to the obesity epidemic in New Zealand or other countries.

Professor Rush says quite simply - over-eating and eating the wrong, energy dense foods which are full of calories, means children in New Zealand - like those in the United States - have become on average 4kg heavier over the past three decades and adults 8kg heavier.

The 2006 - 2007 New Zealand Health Survey found that 1 in 4 adult New Zealanders are obese.

Poorer people at greater risk of obesity

Professor Rush says their research found the rates were higher for the poorer proportion of those tested - she says nutritious food is generally more expensive than less healthy food and puts the poorer section of the population at greater risk of obesity.

So called ‘affordable foods' says Professor Rush are often full of fat or empty calories such as white bread, full-fat milk and cuts of meat with a high fat content, and often people are left malnourished and hungry.

For the study the researchers calculated what adults should currently weigh based on their higher food intake, and compared this to their actual weight - if they weighed more than projected, this would suggest a drop in physical activity - but in fact the researchers found that adults weighed less than could be expected from their diet and Professor Rush says this suggests, if anything, over that period of time, the adults may have been increasing their physical activity, not decreasing it.

As the rates for children were on a par with the adults, the researchers came to the conclusion that changes in physical activity had little or no impact on children growing fatter.

Alarming results

Prior to the study, the researchers assumed that people were in general over-eating by about 100 calories a day, however, the results were far more alarming - it was found that between 350-500 extra calories a day more than is needed is being consumed by many.

In real terms this means says Rush that children would have to cut their intake by about 350 calories a day - equal to one can of fizzy drink and a small chocolate bar, and adults 500 calories - the equivalent of a large burger.

Professor Rush says in today's society, walking an extra two, to two-and-a-half hours a day to burn off the extra calories, is not really an option and we need to be realistic about what physical activity alone can achieve.

Professor Rush says the study shows that in order to influence the underlying drivers of obesity we should be looking more to the ‘energy in' side than the physical activity side as over-eating or eating highly calorific foods are key players in obesity.

Nevertheless says Professor Rush this does not say that throughout life, physical activity is not essential for health and quality of life.

This new research adds to research by Australian scientists which also found that extra calories are to blame for the obesity epidemic.

The US experience

This research by Professor Boyd Swinburn, from Deakin University in Victoria also examined the relative contributions of food and exercise to the development of the obesity epidemic by combining metabolic relationships, the laws of thermodynamics, epidemiological data and agricultural data - it also found that the obesity epidemic in the United States since the 1970s was virtually all due to increased energy / calorie intake.

Professor Swinburn also questioned the assumption that both reduced physical activity and increased energy intake have been major drivers of the obesity epidemic and says their study found that the weight gain in the American population can virtually all be explained by eating more calories and changes in physical activity appear to have played a minimal role.

Professor Swinburn also emphasises that physical activity should not be ignored as a contributor to reducing obesity and should continue to be promoted because of its many other benefits, but that expectations regarding what can be achieved with exercise need to be lowered and public health policy shifted more toward encouraging people to eat less.

The World Health Organisation (WHO) estimates in 2005 were that approximately 1.6 billion adults (age 15+) were overweight; at least 400 million adults were obese and at least 20 million children under the age of 5 years were overweight globally.

The WHO says by 2015, approximately 2.3 billion adults will be overweight and more than 700 million will be obese.

Both studies were presented at the international obesity conference in Amsterdam this month.