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How efficiently do we digest our food compared to machines?

  1. Aug 19, 2008 #1
    How much energy is wasted as we digest and convert our food into energy?
  2. jcsd
  3. Aug 19, 2008 #2
    Sorry, I realized how stupid my question was, and tried to quickly change it before anyone read it. Obviously we are simply harvesting stored energy.
  4. Aug 19, 2008 #3


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    You normally take 85% as the efficency of digestion.
    That is you get 85% of the energy compared to simply burning the food in a calorimeter.
  5. Aug 20, 2008 #4

    Andy Resnick

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    I agree with mgb_phys: my understanding is that our bodies extract out around 80% of the usable calories in food.
  6. Aug 20, 2008 #5


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    It might also depends of your age.
  7. Aug 20, 2008 #6
    Must... Resist... Fart... Jokes!

  8. Aug 20, 2008 #7


    Staff: Mentor

    To put that 80%-85% efficiency in perspective a typical gasoline engine is in the range of 25%-30% efficiency, diesel engines are around 40%, and even fuel cells only reach about 50% efficiency. Not only is biological metabolism much more efficient, but the thing that always amazes me is what a wide variety of fuels we can take compared to an engine where even very small differences in the chemical compositon or purity can dramatically degrade performance.
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