Gluttony (overeating) - not laziness (exercise) - to blame for obesity

• 11:15 19 August 2008
• NewScientist.com news service
• Tamsin Osborne

Greed - not sloth - might be responsible for the obesity epidemic, according to research showing that we're doing just as much physical activity as we were in the early 1980s.

An increasingly inactive lifestyle is often blamed for the soaring obesity rates in the developed world, but few studies have measured whether lifestyle changes have decreased the amount of energy we burn.

To address this, John Speakman of the University of Aberdeen, UK, and Klaas Westerterp of Maastricht University in the Netherlands looked at the amount of energy used through physical activity over the past 25 years in 393 people from across the US and 366 from Maastricht.

In these subjects, energy expenditure has been measured since 1982 using a technique called the "doubly labelled water method", which measures the throughput of water labelled with isotopes of hydrogen and oxygen. By comparing the daily energy expenditure in the early 1980s with current data, the researchers showed that there has been no significant decline in the energy the people studied burned through physical activity.

The obesity epidemic had already started by 1982, but Speakman argues that people have always been fairly inactive during the evenings, and that although activities such as watching TV and playing computer games might be relatively new, they have not affected overall energy expenditure.

"Prior to widespread TV ownership we probably spent this time listening to the radio, before that reading, and before electrical lights were discovered we would have been asleep," he says.

If we are not less active, then we must be eating more food, suggesting that trying to increase our energy expenditure through physical activity may not be the best way of tackling obesity.

"If we want to reverse the obesity epidemic it would be much better to focus on trying to decrease caloric intake," says Speakman.

But Paul Zimmet of Monash University in Victoria, Australia, warns that

a complex problem like obesity requires a complex solution. "Addressing the current obesity epidemic requires an integrated approach over and above modifying energy intake," he says.

Journal reference: International Journal of Obesity (DOI:10.1038/ijo.2008.74)

Nature - full text.