Researchers in the Netherlands published a study looking at the food intake of people eating soup, both when the subjects were focused and distracted.
When subjects were focused, those who took smaller sips consumed 30% less than those who took larger sips. Further, the group taking larger sips underestimated their intake. The study also found that when subjects were distracted, for example, by television or conversation, both small sippers and large sippers tended to eat more as well.
The implication is that if people take smaller bites or sips of food, they can lower their food intake and prevent obesity.