...It's just the way our bodies work. Fasting followed by food in any amount will have a disproportionately fattening effect on the human body due to the way our blood sugar levels and metabolisms operate. This was first observed by American doctors during WW2. After liberating the concentration camps, Army doctors noticed that despite eating regular-sized portions, seriously malnourished and underweight prisoners were not gaining weight. They started experimenting on ways to fatten them up and quickly discovered that they would rapidly gain weight if they were 'starved' during the day and then fed at night - even normal-sized portions. The same logic helps explain why skipping meals, especially breakfast, usually has the opposite effect as intended!