Does it take more energy to "metabolize" fats than for carbohydrates?

Discussion in 'Chemistry' started by WillNever, Nov 6, 2009.

  1. WillNever Valued Senior Member

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    2,595
    Someone told me that eating a lb. of fat would cause you a net gain of energy that is less than eating a lb. of carbohydrates because metabolizing fat "cost more energy." Meaning that even though 1g of fat contains ~9kcals and 1g of carbohydrates contains ~4 kcals, that the fat will still give less energy because of the energy needed to "break it down."

    Can someone clarify, if true? Does metabolizing fat take so much more energy that it gives you a smaller net gain of calories than carbohydrates do? Such things don't sound right.
     
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  3. S.A.M. uniquely dreadful Valued Senior Member

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    No its not true.

    The metabolisable energy (ME) present in one gram of fat is 9 kilocalories. The Net Metabolisable Energy (NME), after correction for losses through heat during metabolism, present in one gram of fat is also 9 kilocalories.

    Compare that with carbohydrate where the ME is 4.0 kcal/gm and the NME is 4.0 kcal/gm

    The heat losses are related to issues other than oxidation [ie energy capture and thermogenesis]

    edit: if you would like more substantive information, here is a good online reference:

    http://www.fao.org/DOCREP/006/y5022e/y5022e00.htm#Contents
     
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  5. ElectricFetus Sanity going, going, gone Valued Senior Member

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    Well I guess if you want to take into account time to metabolize fat verse sugar, your body can metabolize sugar much faster then fat, which is why it put in energy drinks as being so water soluble its being absorbed and metabolized as soon as it hits your gums, fat has to wait for your small intestines and then processing in your liver. Even so the inefficiencies of this processing of hydrophobic molecules are completely made up by fats much higher energy content, fat will provide more energy if not then your body would not store energy in fat!
     
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  7. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    I think what you say is true of fibre.
    Containing unusable calories, it uses excess calories in dealing with it.
    Thus, a slice of high fibre bread containing 100 calories will result in slightly less weight gain than a white slice containing the same number.
    It also remains in the stomach longer, resulting in less hunger, and its roughness has a beneficial cleansing effect on your bowels

    It does make you fart though.
     

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