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How efficient are we?

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Tweefo
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« on: May 04, 2010, 18:44:43 PM »

How good are our bodies turning food into usable energy? My son's biology book (Gr Cool recon it's about 10% but I disagree. A car's engine is about 20 - 25% but it needs fuel (quite concentrated) all the time. Coal fired power stations work on 30%. We mammals can get by with one meal a day for months. The food we eat is also not all potential energy. I think we must be quite efficient but does anybody know?
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Rigil Kent
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« Reply #1 on: May 04, 2010, 19:03:29 PM »

One must first establish what the 10% represents. If you take al the carbon ingested (including that locked up in amino acids and fiber) and divide that into all the carbon exhaled as CO2, then it sounds about right.

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GCG
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« Reply #2 on: May 05, 2010, 08:28:21 AM »

i think, one should see, how much of the original meal consumed, leaves the body as waste.  obviously, in my thoughts anyways, whatever leaves your body, isnt used.
like sellulose in the plant matter we consume.  our bodies simply dont have the ensymes to break that down into something usefull.
allso, if we had to consume bone, i doubt our bodies would be able to make much of it.
maybe, back in the day, when we actually had to work for our meals, our bodies were better at using whatever nutrients was supplied to it.  digest better, burn the energies better.  but as the millenia progressed, and our abilites to process raw materials advanced, our bodies became lazy.
i think, that if you were to be standed in a situation where you had limited food supplies, your body would kick into gear, and be more efficient at processing the food you eat.
when you eat more, your body doesnt have to work all that hard to translate the raw materials into energy.
my opinion anyways, not based on any facts.
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StevoMuso
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« Reply #3 on: May 05, 2010, 10:30:18 AM »

... your body would kick into gear, and be more efficient at processing the food you eat.
when you eat more, your body doesnt have to work all that hard to translate the raw materials into energy.

Sounds logical to me. We don't need that much energy anymore coz we have become less physically active as a species. Maybe our bodies are capable of processing food more effectively and getting more nutrients from our food, but since we are not consuming much energy we don't need so many nutrients. So nutrients are either stored for future use, and not getting used so turning into overweight situations, or in the lucky ones, being passed unused and unprocessed through the system.

Makes sense to me.
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« Reply #4 on: May 05, 2010, 12:00:11 PM »

Beyond how efficient we are at digesting and utilising our food, we should also look at heat loss.   The case of the car's engine actually tells us that a vast amount of energy is not converted into motion, but into heat.   The same applies for the coal fired power station.   I recall that the energy efficiency of a steam locomotive is shockingly poor.   This would suggest that coldblooded reptiles may be more fuel efficient than us, but I'm guessing here.   Our ability to put on and take off clothes could make us more efficient than other mammals. 
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