Metabolism makes diet numbers go awry

National guidelines that advise people how to lose weight are seriously flawed and grossly overstate how quickly they will reach their targets, scientists say.

National guidelines that advise people how to lose weight are seriously flawed and grossly overstate how quickly they will reach their targets, scientists say.

Researchers found people lost only half as much weight as expected in a year if they followed the advice given by the NHS and US health organisations.

The problem came to light when scientists at the US National Institutes of Health in Maryland realised standard weight loss advice failed to account for changes in metabolism as people lost weight.

The rule of thumb used by the NHS and other health services assumes that if a person cuts 500 calories from their daily diet, they will lose about 450g (1lb) each week, regardless of how long they adhered to the regime. But as people lose weight, their metabolism slows until they reach a new stable bodyweight.

"Dietitians have used this rule of thumb for a long time, but it turns out to be completely wrong. It doesn’t account for metabolic changes that happen when people change diet," said Kevin Hall, who led the research.