Don't Trust Your Stomach

 
Dr. Brian Wansink and his research team rigged up some interesting soup bowls that were connected, beneath the table, to a pipeline that continuously fed tomato soup into the bowls.
One group of eaters in his experiment ate their tomato soup from regular bowls and the other group ate from the bowls that refilled themselves. The diners did not know that their bowls were constantly refilling. All eaters were instructed to eat until they felt full. Those whose bowls refilled ate 73% more food than those eating from regular bowls.
Even though they ate so much more, none of them claimed to feel full. In fact, one eater when asked if he was full (because he had consumed almost a gallon of soup) looked down at his bowl which was half full and said, "Why would you think I'm full? I still have half a bowl to go."

Source: Brian Wansink, James E. Painter and Jill North, "Bottomless Bowls: Why Visual Cues of Portion Size May Influence Intake." Obesity Research.

TIP Choose your portion size by measuring it or weighing it. Don't wait until you feel full to stop eating.