“Researchers have found that people who begin their meals with a simple vegetable soup eat about 20% fewer calories than those who don’t. It doesn’t matter if the soups are chunky or pureed, only that they’re low in fat and calories (no cream soups). The water content of the soup is the key–it adds volume to fill you up. If you think you can get the same effect by having a glass of water with your meal, think again; the phenomenon seems to work only when the extra water is part of the dish.”
Or, want a quick, just-add-water soup? Try instant miso soup.