Someone once told me it is possible to have a net weight gain of more than what you eat. For example if you eat a quarter pounder burger you can potentially gain more than 1/4 pounds. Is this true?
No, because of the law of conservation of mass. You'll develop fat at different rates from different foods, and foods that are high in fiber or low in nutritive content won't contribute as much to your long-term weight gain, but ultimately you cannot possibly gain any more weight than that of the matter you consume; any statement to the contrary is simply ridiculous.