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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?

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Related: physics.stackexchange.com/questions/2605/… –  Sklivvz Apr 30 '11 at 23:12
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Evil plan: We could feed 1kg of lion meat to tigers, and get 2kg of tiger meat to feed to lions to get 4kg of meat, and... hey we just solved world hunger! –  Sklivvz Apr 30 '11 at 23:45
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@user unknown: I was assuming for the sake of argument that nuclear fusion does not, generally speaking, occur within the human gastrointestinal system. ...Yet. –  Jon Purdy May 1 '11 at 0:42
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Maybe this is how the breatharians do it. –  Kyralessa May 1 '11 at 3:41
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Sort of. Everyone else has answered from the conservaton-of-mass perspective. However, a 1/4 pound cheeseburger is made from 1/4 pound of meat, ergo the 1/4 lb. does not include the bun, cheese if you like, lettuce, tomato etc... Therefore, it is theoretically possible to gain more then a 1/4 lb. from eating what is commonly referred to as a "1/4 pound hamburger", but that is simply because the assembled hamburger itself weights more then 1/4 lb. –  Fake Name May 1 '11 at 8:33
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up vote 31 down vote accepted

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.

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As a side comment, putting on more weight than one eats would be also absurd from the point of view of weight gain velocity. One eats more than a kg of food every day, or almost 400kg of food per year (60 stones). –  Sklivvz Apr 30 '11 at 23:15
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@Sklivvz: Right. Further, even if you were comatose and burning absolutely as few calories as possible, you'd still need to be using some energy to keep your heart beating and your brain functioning. –  Jon Purdy Apr 30 '11 at 23:22
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Keep in mind, when you eat a "quarter pound" burger, that is just the weight of the meat in most instances. You are actually eating a lot more than that since there are condiments, bun, and other stuff added on. –  Skava May 1 '11 at 0:00
    
I get what you say and it makes perfect sense, I must say I'm confused though. Ruminants get incredible amount of energy (resulting in weight gain eventually) from grass etc. I'm looking into it. –  Trufa May 1 '11 at 3:01
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You can gain more weight than what you eat if you weigh your food at a higher altitude than where you weigh yourself. –  Flimzy Nov 9 '12 at 20:32
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