Scientists have discovered why the Atkins diet is so successful at helping people lose weight.

Curbing carbohydrates actually reduces overall appetite so people on Atkins-type diets shed more kilograms more quickly, research has shown.

The small study involved just 10 volunteers who were confined to hospital for three weeks so that every calorie they consumed and expended could be measured.

It revealed that carbohydrates eaten by the volunteers - potatoes, bread and cakes - stimulated their appetite so they ate more of other foods as well.

When the carbs were restricted, consumption of other foods fell as well, even though the volunteers were free to eat anything else they wanted.

Over the three weeks of the study the average daily consumption fell by a third from 3111 calories a day to 2164 calories, when access to potatoes, bread and cakes was restricted. The volunteers, who were obese and had diabetes, lost 1.6kg on average.

Many claims have been made about the way the Atkins diet disrupts the body's metabolism to encourage weight loss. But Guenther Boden, professor of medicine at Temple University, Philadelphia, who led the study, said this was a myth.

"We proved that people lose weight on the Atkins diet because they eat less, not because the carbohydrate calories are treated differently by the body," he said.

"Participants went from an excessive caloric intake to a normal caloric intake for their height and weight when we reduced their carbohydrates. This indicates to me that it was the carbohydrates that stimulated the excessive appetite."

At the start of the study the volunteers were eating 300g a day of carbohydrates but these were cut to 20g a day at the end of the first week.

Overall consumption fell by 1000 calories a day, even though the participants were offered as much protein and fatty foods as they could eat.

The researchers weighed all food, monitored exercise and measured calorie energy intake, expenditure and body water composition and tested blood sugar, cholesterol and hormone levels believed to be involved in appetite regulation.

"All the weight loss was in fat," Professor Boden said. "We weighed and measured every calorie that participants ate and every calorie they spent. We knew what went in and what went out.

"On the very low carbohydrate diet participants spontaneously reduced their calories by about 1000 a day. One gram of fat equals nine calories so, doing the maths, you can determine how much fat will be lost by cutting 1000 calories."

He added: "You don't have to cut carbs as drastically as participants did. If you cut carbs modestly, you cut calories and you'll lose weight.

"It helps to know that carbohydrates make it more difficult to reduce food intake. So cutting the carbohydrates at least to some extent will help keep down the caloric intake.

"With fewer carbohydrates you are going to eat fewer total calories a day."

The study is published in Annals of Internal Medicine.