Dieting just got twice as difficult

Everything you know about dieting is wrong, say US scientists who have devised a new formula for calculating calories and weight loss that they hope will change the way people tackle obesity.

Losing weight just got twice as hard because of a new way of calculating the effects of dieting.

Conventional weight loss guidelines fail to take into account changes in metabolism, according to US expert Dr Kevin Hall.

As a result, dieting is always going to be a struggle, he argues. Cutting calories leads to a slowing of the metabolism, which means it takes longer to lose weight.

At a rate of 100 calories lost per day, it would take the average person a year to shed 5lbs of body weight.

Under the previous guidelines, based on the idea that 1lb is equivalent to 3,500 calories, the same degree of weight loss should be possible in roughly half that time.

At the annual meeting of the American Association for the Advancement of Science, Dr Hall said: “People have used this rule of thumb to predict how much weight people should lose for decades now, but it turns out to be incredibly wrong.

“The reason it’s wrong is because it doesn’t account for the metabolic changes that take place when people change their diet.

“We know that if you cut the calories in somebody’s diet their metabolism starts to slow down, and it slows down more and more the more weight that is lost. So eventually you’ll reach a plateau.

“Some of my work has been to develop realistic mathematical models about what happens to metabolism when people start changing their diets and can we come up with some better rules and better predictions.”

Due to of the way in which the metabolism slows weight loss, dieting away 100 calories daily would lead to the loss of just 10lbs in three years, said Dr Hall, from the Laboratory of Biological Modelling in Maryland.

Five pounds of that weight loss would go in the first year.

Dr Hall has developed an online slimming aid that explains what level of dieting is needed to achieve a weight loss target. The model takes into account numerous factors, including metabolism.

The slimming aid — available at bwsimulator.niddk.nih.gov — is designed to assist researchers rather than members of the public, although anyone can access it.

“Instead of using that old rule of thumb that we now know is incorrect, people can plug in what their goal weight might be in a specific time period,” said Dr Hall of the slimming aid.

“What the model will do is simulate what changes in diet and exercise that person will have to do to achieve that goal weight and even more importantly what they have to do permanently to maintain that weight loss.”