<human>: Can you give me a shortened version of the text?

So just chatting along with a friend when we got on the topic of diet (as in what you eat, not "dieting") and weight. She was under the impression that you can not gain more weight than the weight of the food you consume. I said that my understanding was that it didnt matter how much the food weighed before you ate it, that it's the amount of calories per day that affect your weight gain.

As an example, I took rice crispy treats. They are very light and airy and certainly dont weigh much.  But they are packed full of calories and carbs, and could easily push one over 2,000 calories for the day while only consuming a few oz of the stuff. Thus you'd gain more weight than what you consumed. She doesn't understand where the 'extra' weight comes from then, if not from the food itself.
<bot>: Is it possible to eat, say, .5lbs of food and gain 1lbs of weight as a result? If so, where is the additional weight coming? The water you cosume during the day?