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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
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
You can, if you a) drink 2 liters of cola meanwhile or b) implement the opposite of nuclear fusion inside your body (see 'conservation of mass' @Purdy) E=mc². –  user unknown May 1 '11 at 0:21
@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
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

4 Answers 4

up vote 41 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
@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
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
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
-1 you seem to have forgotten that humans also breathe. It's entirely possible that, after eating, there's some process that causes us to exhale less than we inhale, which would cause a (possibly significant) net gain in weight. I doubt that's true, but it needs to be considered. –  BlueRaja - Danny Pflughoeft Nov 10 '12 at 0:08

No, this isn't possible, here's why:

  • I weigh 70KG
  • I eat 1KG of any food
  • Immediately after eating I will weigh 71KG
  • Some time after eating my body will digest the food and process it, some of it will be excreted, and some will be converted and stored as fat. Now I weigh less than 71KG.

The key is that nothing can be made to weigh more than it currently does. No process or conversion procedure exists that would increase an object's weight, this is known as the law of conservation of mass.

Further explanation:

All your food can be broken down into atoms, each atom is a single element, all elements are listed in the periodic table alongside their weight.

When your body processes your food, some will be converted to fat and stored, this is a change in the food's chemical composition, the atoms in your food are mixed up to form new compounds but they are all still there and still weigh the same.

Also, I found this short explanation and video that demonstrates how an object's weight doesn't change when its state changes.

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This answer has the same problem as Jon Purdy's: it neglects respiration. –  Ben Crowell Sep 7 '14 at 0:08
@BenCrowell But respiration would cause the loss of even more weight. I have already explained why this isn't possible, it wasn't nessesary to mention any other reasons. –  Drahcir Sep 7 '14 at 9:31

No and here is why. The conservation of mass has already been mentioned. Because we are dealing with chemical processes, mass-energy conversion is completely neglible. It means that if you put someone in a glass chamber, seal it (it's big enough, so no problem breathing) and measure the mass (normally only by weight, so no moving inside) it will always retain the same mass as long as the content does not change. You can eat an hamburger or work out hundred hours on a home trainer, the mass will stay constant.

This is really a very annoying logical error in e.g. Prometheus or Alien where monsters are growing rapidly without recognizable food source. Nothing can grow without eating much more than they gained weight.

What is possible is gaining mass by hidden processes. Trees for example do not gain mass from the earth they are growing in, but extract their complete mass by inhaling carbon dioxide and using sun light as energy to extract the carbon from the inhaled carbon dioxide. No carbon dioxide => trees cannot grow. Fungus can grow because it is able to transform almost all cellular materials for his own growth. Bacteria consume food like us, only smaller.

If we eat exactly 1 kg, we will see that without glass chamber we will not gain exactly 1 kg. We lose weight by water vapor and breathing. We eat food and inhale oxygen and the result is energy and carbon dioxide which we exhale.

If you want to gain mass, you must consume mass. No exceptions.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

You need to references your contributions, the conservation of mass does not support your assertions on how trees gain mass, how we lose mass, etc. –  Sklivvz Sep 8 '14 at 20:24

Yes, it is possible. Burgers contain salt. Salt causes water retention.


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You still need to ingest the water, so the total is less or equal than what you eat. On the other hand, if we don't include ingested water in the total, the claim is trivially true even without counting water retention. –  Sklivvz Sep 4 '14 at 14:03
Well if the term "weight" completely excludes and biological process necessary to preserve life, such as drinking water or respiration, or metabolism, then the correct answer obtained by correctly applying the law of conservation of mass, is that after any act of eating your new weight is exactly the sum of your weight before eating and the weight of the food. –  Steven P Sep 6 '14 at 14:51
If you include merely the biological process of respiration (breathing) then your weight after the meal can be either more or less than the sum of your previous weight and the meal because of the stochastic nature of oxygen exchange in the lung. If you want to wait long enough for metabolism to happen (as the popular, but incorrect answers presuppose) then you have to let that experimental subject drink too---unless you mean to kill him. –  Steven P Sep 6 '14 at 15:00
You do not eat water. The question obviously is excluding any atoms added to the body thorough other methods like drinking and breathing, or skin absorption. –  Jonathon Wisnoski Sep 8 '14 at 16:08
If you only count eating solid foods, then the claim is trivially false. There are liquid diets which can be fattening. Also, water retention is not permanent, so it's a bit of a stretch to say it's a "gain". –  Sklivvz Sep 8 '14 at 21:53

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