I have occasionally remarked, you can't gain more weight than the weight of the food you eat, because conservation of mass. This is sometimes my response to people who don't eat a single donut on a special occasion. Naturally the pound or less of food you might eat in a day is not permanently conserved. I also think that a pound of food sounds like an enormous amount, but it really isn't. If you like hamburgers (and let's say you make your own so they are wholesome) you might cook a third of a pound of ground meat to make one.