Dieting is harder than we think

Scientists have debunked decades-old theories on losing weight and developed a more sophisticated measure of weight loss, which takes account of metabolic changes and of differences between fat and thin people.

For decades, doctors have based their advice to those who want to lose weight on the assumption that cutting 500 calories a day will see the weight fall off at the rate of 1lb a week.

`This is wrong,` Kevin Hill, of the National Institutes of Health in the United States, said. `It does not happen.`

Also read: Dieting tips for those at work

The error has arisen because the calculation did not take account of changes in metabolism as weight falls. The body adjusts to reductions in energy intake (calories eaten) by slowing its energy output (calories expended).

The result is that forgoing that daily chocolate bar containing 250 calories will lead to about 25lb of weight loss if it is sustained for three years, much less than the 78lb predicted by the old dieting assumption.

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