Researchers call it Greed! Yes, greed, and not laziness, is to be blamed for the obesity epidemic.
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 labeled water method", which measures the throughput of water labeled 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 says 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," New Scientist quoted him, as saying.
"If we want to reverse the obesity epidemic it would be much better to focus on trying to decrease caloric intake," Speakman added.
The study has been published in the International Journal of Obesity.