Well this explains everything....

The size of your stomach size alone--and not the size of your body--affects your feeling of fullness during a meal and thus how much food you want to eat, reports Reuters of new research from the Mayo Clinic College of Medicine in Rochester, Minnesota. The most important takeaway: The factors that control our stomach volume could be the best way to fight obesity.

The Mayo Clinic researchers found that people who were overweight or obese took longer to feel full and needed more calories at mealtime than people of normal weight. What's most interesting is that this is not a simple correlation of bigger people having bigger stomachs. Instead, it is fasting gastric volume, which is the size of a person's empty stomach, that is directly related to the feeling of fullness--no matter how large or small the person's whole body.

Even the researchers were surprised by this. Lead study author Dr. Michael Camilleri told Reuters that body mass index (or BMI) is independent of fasting gastric volume. He suggested that changes in diet or the patterns of food intake, such as eating several small meals throughout the day, could help control a person's stomach volume and help with weight loss. The research findings were published in the journal Gastroenterology.