Abbas Dhanani asked:
If I stood on weighing scales while holding a big juicy burger would my total weight change if I ate the burger? I always thought I'd get lighter but I can't reason why.
Chris - I would argue that, actually, the burger is already mass in your hand on the scales and therefore, if you put it into your mouth, it just turns into mass in your body.
There would then be some metabolism, obviously, because you’ve got to exert some energy to work the muscles of mastication to chew up the burger. And to produce some saliva; you’ve got to warm your body which means you're burning some energy doing that as well and you presume the burger is going to be a bit lower than body temperature probably by the time you’ve done your experiment.
So there's a little bit of a loss of energy there. So, that means you're going to lose a little bit of mass. Metabolism that’s going to carry on as you digest the burger as well, because you got to break it down into its component parts and absorb it. I reckon in the short term, no change. In the long term, there’d be a modest small reduction in mass...
Max - How accurate your bathroom scale is?
Chris - Well, that was going to be my bottom line, if you excuse the pun, because I was going to say that actually, you're talking about trivialities. Once the burger goes in, the burger becomes part of you. There will be some losses to the toilet though and so, a certain amount will be absorbed and a certain amount won't be absorbed. And so, you won't get all of the energy turning into mass. But let’s assume that none of the burger is wasted. It would all get converted either instantly into sugars that you would burn or fat that you would store, so your body mass would reflect the increase in weight gain owing to the burger...
The scale would measure your weight as the same both before and after you ate the burger. The scale doesn't care whether the burger is in your stomach or in your hand; you weigh the same when added together either way. Supercryptid, Fri, 11th Mar 2011
For dieting purposes, no, chemical breakdowns don't change the weight of the chemicals in question. A hamburger takes several forms after being digested: carbon dioxide gas which is exhaled from the lungs, fat that is stored in the body, liquid and solid waste, plus perhaps other things like sweat. Add the weights of all of these things together and you will get the same weight as the original burger (plus the oxygen used to "burn" the calories in it). Supercryptid, Tue, 15th Mar 2011
Abbas Dhanani asked the Naked Scientists:
I swear my stomach and thighs get bigger by every bite! Maizie, Wed, 24th Jun 2015
You are losing weight all the time (ignoring the mass of air being breathed in and out which causes fluctuations up and down if you include it), but if you eat the burger you will lose weight a bit faster as you munch and swallow it, even before you start digesting it. Some of the energy will be lost as sound and other vibrations (in addition to heat), but all of that lost energy starts as energy released from the rearrangement of bonds between atoms where a process similar to combustion is going on. David Cooper, Thu, 25th Jun 2015
PmbPhy, Thu, 25th Jun 2015