The trick to losing weight and keeping it off is learning to recognize feelings of hunger and satiety, so that you eat only when your body tells you to, instead of when your mind wants you to.
Goldfish do not have the feeling of satiety when they are full, like humans do, so if you let them, they will eat and eat until it kills them.
Before dinner the children were hyperactive, but after dinner their satiety made them groggy and sleepy.