How much energy is wasted as we digest and convert our food into energy?
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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