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BIRMINGHAM: Lack of exercise is not the cause of the obesity epidemic, said biologist John Speakman, who has found that we do not exercise less nowadays.
Speakman, from the University of Aberdeen, has collected data showing that too much food, not too little exercise has caused us to pile on the pounds.
What's more, he added, small lifestyle changes such as building in a half hour walk every day will not be enough. According to his model, drastic dieting may be the only option other than medical intervention, said Speakman, who presented his results at the British Science Festival.
The cause of obesity
The results could have wide implications for combating obesity. According to the 2008 National Health Survey, about a quarter of Australians are obese, defined as having a body mass index (BMI) over 30.
Researchers trawled through the literature to find studies from the 1980s onwards that used a 'doubly labelled water technique' to measure energy expenditure. They used data from 759 participants across North America and the Netherlands, and found that there has been no significant decrease in energy expenditure over the past 25 years.
On the other hand, said Speakman, Food and Agriculture Organisation (FAO) data has shown that food sales have gone up. The amount of food purchased (in calories per capita) has increased by 22% in the U.S. and 12% in Britain between 1972 and 2007. Speakman acknowledged this could be the result of us wasting more not eating more, but he noted that sales of non-perishable foods such as chocolate, which are less likely to be thrown out, have also increased.
Walk for 4 to 5 hours a day
Speakman's team used a model to predict weight loss, which took into account the extra energy overweight people burn when they move. For a person with a BMI of 35 to reduce their BMI to a healthy level, they would have to walk four to five hours a day or reduce their calorie intake by 30% - small changes in daily routine would not be enough.
"Although exercise has many health benefits, weight loss is not one of them," Speakman said.
However, Gail Trapp from the Exercise Physiology Unit at the University of New South Wales thinks Speakman is "oversimplifying the issue".
"When you examine the problem from a purely energy in - energy out equation, his thesis is logical. But we have shown that you can induce significant weight loss with physical exercise alone. I agree that small changes in daily living are not going to be terribly effective, but like anything, you can change the way you do things to make them more effective."
Speakman emphasised that we should still exercise.
"[It] has many benefits," he said, "and should be promoted as part of a healthy balanced lifestyle." But, he maintained, in order to beat obesity, the amount of exercise required is "unrealistic" in modern society. "Although exercise has many health benefits, weight loss is not one of them."
