Besides being delicious, soup has a positive function as part of a healthy diet. In fact, a Wall Street Journal article, “Eat Big Food” explains why eating soup helps weight control.

“A Pennsylvania State University study fed normal-weight women over two days. The women ate as much as they wanted of different types of high-calorie and low-calorie foods.

When researchers tallied the women’s intake, they found the women instinctively ate about three pounds of food a day. The calorie content didn’t seem important to the women in determining how much they ate–even when it dropped by 30%. In other words, the women seemed satisfied by a certain volume of food, not calories.

So the trick for the dieter isn’t to eat less food, but to pick foods that pack relatively few calories by weight, says Barbara J. Rolls, the Penn State nutrition professor and author of the “volumetrics” diet books. An easy way to do this is to think big. Choose foods that are bulked up by water or fiber. For instance, for 100 calories, you can eat a quarter-cup of raisins or two cups of grapes. Adding vegetables can double the size of a pasta dish without much of a calorie increase.

Soups are also big food – even though liquid calories usually don’t satisfy hunger. The reason could be psychological, or it may simply be that soups are more substantive, so the body treats them as a food.

The difference soup can make is startling. In one study, women were given 1 1/3 cups of chicken-rice casserole and a 10-ounce glass of water to drink. Another day, the water was mixed with the casserole, turning it into 2 cups of soup. Both portions contained 270 calories.

After the main course, the women could eat other foods. The casserole group consumed 396 calories for lunch. The soup group stopped at 289 calories. The body, it appears, didn’t factor in the water when it was consumed as a beverage, but bulking up the casserole with water made the meal more satisfying.”