Eating soup with a meal could be the answer to the obesity crisis, according to scientists in the US.

People who fill their stomachs with soup at the start of a meal eat less overall, research shows, and rather than piling on the pounds, the addition of the extra course can actually help people lose weight.

The soup regime is recommended by researchers at Pennsylvania State University, who tested it on volunteers. They found that when participants ate a first course of soup before a lunch entrée they reduced the total calorie intake of their meal by a fifth compared with those who ate the entrée alone.

But they stressed that the soup must be low-calorie. Adding a creamy soup to the meal would be likely to have the opposite effect and boost the total calorie intake and lead to weight gain.

The research, supported by the National Institutes of Health, was presented to the Experimental Biology conference in Washington, yesterday.

Barbara Rolls, professor of nutrition and co-author of the study, said it had built on earlier work into the role of low-calorie soup as a way of reducing food intake.: “Earlier work suggests that chunky soup may be the most filling type, so the purpose of this study was to determine whether different forms of soup might have different effects on food intake.”

Four styles of soup - separate broth and vegetables, chunky vegetable soup, chunky pureed vegetable soup and pureed vegetable soup - were studied.

The scientists had thought that the thickness of the soup or the amount of chewing required would affect how filling it seemed. But the results from testing the four different varieties using the same low-calorie ingredients blended differently showed that it made no difference.

Julie Flood, who led the study, said: “Consuming a first course of low-calorie soup in a variety of forms can help with managing weight. Using this strategy allows people to get an extra course at the meal, while eating fewer total calories.

“Make sure to choose wisely by picking low-calorie, broth-based soups that are about 100 to 150 calories per serving. Be careful of higher calorie, cream-based soups that could increase the total calories consumed.”

In a separate study at the university, researchers helped children eat less by using a similar strategy - incorporating low-calorie vegetables into a pasta sauce to “bulk” it out.

Persuading children to eat vegetables is universally recognised to be difficult, but by including them in sauces and soups - as “stealth vegetables” - they help reduce the total calories eaten.

In a study of 61 children aged from three to five, the researchers provided two pasta sauces - one of which included broccoli and cauliflower blended into the sauce which reduced the calorie content per serving by a quarter. Kathleen Leahy, who presented the results to the conference yesterday, found children who ate the pasta with the lower calorie sauce consumed 17 per cent fewer calories overall. “The kids could not really tell the difference and ate a consistent weight of pasta,” she said.