How efficiently do we digest our food compared to machines?

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Discussion Overview

The discussion centers on the efficiency of human digestion compared to mechanical engines, exploring how much energy is wasted in the process of converting food into usable energy. Participants consider various factors influencing digestion efficiency, including comparisons with different types of machines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the energy wasted during digestion and how it compares to energy harvesting.
  • Another participant suggests that digestion is primarily about harvesting stored energy, indicating a shift in perspective.
  • It is proposed that digestion efficiency is typically around 85%, meaning that 85% of the energy in food is extracted compared to burning it in a calorimeter.
  • Another participant agrees with the 80% efficiency figure, indicating some consensus on this estimate.
  • There is a suggestion that digestion efficiency may vary with age.
  • A participant humorously refrains from making jokes related to digestion, indicating a light-hearted tone in parts of the discussion.
  • One participant compares human digestion efficiency to that of gasoline and diesel engines, noting that biological metabolism is significantly more efficient and highlighting the versatility of biological fuel sources.

Areas of Agreement / Disagreement

Participants generally agree on the efficiency range of digestion being around 80%-85%, but there are differing views on the implications and factors affecting this efficiency, such as age. The discussion remains open regarding the comparison with mechanical engines.

Contextual Notes

Some assumptions about the efficiency figures are not explicitly defined, and the discussion does not resolve how age specifically influences digestion efficiency.

sketchtrack
How much energy is wasted as we digest and convert our food into energy?
 
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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.
 
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.
 
I agree with mgb_phys: my understanding is that our bodies extract out around 80% of the usable calories in food.
 
It might also depends of your age.
 
Must... Resist... Fart... Jokes!

:-)
 
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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