Calorie counters are on a hiding to nothing

Losing weight is now twice as difficult, thanks to a new way of calculating the effects of dieting.

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

As a result, Dr Hall argues, dieting is always going to be a struggle. Cutting calories leads to a slowing of 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 5lb of body weight.

Under the “old” guidelines, based on the idea that each pound is equivalent to 3,500 calories, the same degree of weight loss should be possible in roughly half that time.

Speaking to the American Association for the Advancement of Science in Vancouver, 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.”