Obesity linked to activity level, says scientist

Some people blame it on genes, others on slow metabolism, but, after all the arguments, obesity is caused by a very simple energy equation, according to a scientist from the UK Medical Research Council. "There really isn't anything magical about metabolism," said Dr Andrew Prentice, of the MRC, in Cambridge. Scientists had been researching obesity for decades, much of it trying to understand the possible genetic role.

"We know that genes are important but it is only one part of the wider picture," he said. Obesity was based on a simple formula - energy taken in, minus energy used up, equalled the change in how much fat the body would store. "Let no one try to dissuade you from that simple logic."

He said the gradual tendency of Western populations towards obesity was a long-standing phenomenon, with records indicating a gradual increase in British average body weight over the past 70 years. "It's not just something that has been going on over the past 10 years."

There were pressing reasons for understanding the causes of obesity, a condition which cost the British taxpayer an estimated £2 billion in health costs every year. Overweight men were 40 to 50 times more likely to develop adult diabetes; women 90 to 100 times more likely.

He described a series of studies and experiments aimed at understanding the mechanisms of obesity. The notion of having a "slow" metabolism was untrue for most obese persons.

He said repeated studies found that overweight people expended more energy than lean people, in part because of the energy needed to carry extra weight. This, in turn, demanded a higher food intake to maintain an unchanged body weight. Studies during which lean and obese subjects were overfed caused similar weight gain in both groups and weight losses were comparable if subjects were under-fed.

There was, however, a paradox as the UK population was eating less per capita than it did a generation ago. Therefore, the tendency towards obesity was not simply about how much people ate but what they ate and their level of activity.

People's energy demands in the past were met largely by carbohydrates (starchy foods) but now a large part of the energy demand was met by fat intake.

A lack of activity was also a key factor as insufficient energy was being used up. People watched an average of 28 hours of television per week and were not active enough to use up the energy consumed.