Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Hot food = more energy for your body?

  1. Jun 6, 2006 #1
    Is it true that if you take the same food, same amount and everything except one serving is heated and another is not. Would the person eating the heated serving get more nutritional value from it in the form of more energy? This comes about from the larger potential energy stored in the bonds of the food that has been heated.

    An anology on a much larger scale would be dead leaves that gets buried or squashed underground and over million of years serve to become fossil fuel. The vast energy does not come from the leaves themselves but from the potential energy accumulated by converting gravitational energy (through squashing) into molecular energy stored in the leaves to become a fuel.
     
  2. jcsd
  3. Jun 6, 2006 #2
    I really doubt it.

    My guess, (and since I'm in NO way any kind of expert in the area, that's all it'd be, a guess), is - no.

    The reason I say that is this. By the time your body has broken down the material you ingest into things like sugars etc, that it can actually use to derive energy from, that material has been in your body MORE than enough time to cool back down to (or, in the case of things like ice cream, even warm up to) your core body temp.

    By that I mean - although the *process* of digestion starts as soon as things hit your stomach (in fact arguably as soon as you start chewing it), that process involves MUCH more than just instantly sucking chemical potenial energy out of the material you ingest. Your stomach is doing one HECK of a lot of "prep work" breaking things up, followed by your intestines doin' their "thang", etc., all just to get that material to the point where your body can derive energy from it, and by that time, it's been in there quite a while, MORE than enough time to cool down to, or warm up to, your core body temp.

    Make sense?
     
  4. Jun 6, 2006 #3
    I would also say that for the most part in terms of practical reasoning, it doesn't matter. BUT theoritically when you digest foods of different temperatures of course there is an effect.

    If the food is too cold, it can do several things.
    (1) extremely cold or hot food will damage the cell lining of your digestive tract which includes your throat, esophagous, stomach etc. The damage will induce repair which "costs" energy.
    (2) cold food will steal heat from the body's own physiologically maintained temperature and will therefore require energy indirectly to return to normal physiological temperature (known as homeostatic temperature/conditions)
    (3) food that is a little warmer will then the body to the point that it doesn't damage, will minimize heat loss that occurs in (2) and will therefore be more energy efficient then cold food.

    But in terms of the molecular digestive process, your body equilibriates the food to the tempearture of your body fairly quickly.

    This also occurs with the air you breathe. When one exhales the air's temperature has increased in a short period of time.
     
  5. Jun 6, 2006 #4
    I would say no but for a different reason: Your body uses a more structured form of energy to work, chemical energy from the foods you eat.

    My suggestion is that your body would get more energy, but it would still just be heat energy, and a 'hot muscle' is not necessarily healthier one. Not that the heat would get to any muscles.
     
  6. Jun 6, 2006 #5
    I would say that heating food can induce certain chemical changes. Some chemicals may effectively burn. Others such as sugar will decompose into simpler and more stable chemicals. I also suspect, and I'm not sure about this, that large molecules such as proteins and vitamins will break down. The effect of this is that cooked food will be less nutritious. Also the broken down chemicals will not have lost their energy. Thus this energy can no longer be absorbed by the body.

    That being said, if you are at some very high altitude, in say the Himalayas, and made the mistake of wear a t-shirt and shorts, you may benefit by drinking boiled yak's milk. If the milk is hot, you will loose significantly less energy through shivering.
     
  7. Jun 6, 2006 #6

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    From what I've read, I would expect that mammals or other endotherms in a gernallly cold climate would need less total calories to maintain their weight if their food was warm. The warmth of the food would reduce the calorie expendeture needed for body temperature maintenance, slightly. This would only apply in a cold climate.

    Ectotherms (animals without temperature regulation) would probably actually need more calories with warmer food - increasing their body temperature due to the warmer food would generally tend to increase their metabolism.

    For the later point see
    http://www.depauw.edu/acad/biology/Websites/kevinkinney/Lab 11B-Temperature.html

    (not sure how long this link will work, it looks like the sort of link that might disappear very quickly, but it was quite interesting)
     
  8. Jun 6, 2006 #7

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    There would be a small indirect energy benefit to the body in the sense that the body would not have to use its metabolic heat to warm up the food to body temperature.

    I don't quite get the analogy. Interesting concept though. I don't see how, thermodynamically, gravitational pressure would put that much energy into the organic matter. There just is not that much work done in the compression. Pressure definitely changes the organic matter chemically over a long time. But the energy is ultimately from the organic compounds made by the plants during photosynthesis.

    But I may be quite wrong. I would like to see a source that analyses the energy input from gravitational pressure to support your contention that the vast amount of energy in fossil fuel comes from the gravitational potential energy.

    AM
     
  9. Jun 7, 2006 #8

    Why do you think diamonds are found in nature? They are just pure carbon but recquire pressures of over 15 atms to naturally occur.

    Similarly one form of fossil fuel, oil use to be carbon based matter but over millions of years, 'eventually turned into oil under great pressure and heat'.

    'More and more rock piled on top of more rock, and it weighed more and more. It began to press down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over millions of years, it turned into coal, oil or petroleum, and natural gas.'

    http://www.energyquest.ca.gov/story/chapter08.html

    The law of conservation of energy says that gravitational energy must be manifested somewhere or be converted in another form. In this case, chemical energy.

    I also remember from a biological lecture that the energy one gets from drinking petrol is far greater than any other source of food. Although you will probably die from doing that.
     
  10. Jun 7, 2006 #9
    From what I gather, the answer to this question is 'yes' but only in the sense of less energy loss => more energy for your body.
     
  11. Jun 7, 2006 #10

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    Just to be clear, changing the temperature of food has NO effect on its nutritive value which ultimately relates to nutriment reaching the cells. Regarding thermal content, the body will regulate itself to eliminate excess heat in the case of hot food but will work to suppress heat loss in the case of cold food.
     
  12. Jun 7, 2006 #11

    LURCH

    User Avatar
    Science Advisor

    When meat is heated, it gets easier to chew. Does this mean that the molecular bonds are looser? And if so, does that also make it easier to digest?
     
  13. Jun 7, 2006 #12

    DaveC426913

    User Avatar
    Gold Member

    Except that many nutrients are destroyed by heating (in the form of cooking). Fresh veggies for example are much more nutritious than cooked veggies.
     
  14. Jun 7, 2006 #13
    Umm...I have read cooking certain food stuffs like carrots and tomatoes actually increases their vitamin content. :smile:
     
  15. Jun 7, 2006 #14

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    All that says is that pressure and heat from the earth changed the chemical structure of the organic matter. It is not saying that the pressure and heat gave fossil fuels most of their energy. That comes from the organic compounds produced by the organisms before they died.

    AM
     
  16. Jun 7, 2006 #15

    Tide

    User Avatar
    Science Advisor
    Homework Helper

    The OP's premise was that everything is the same but the temperature.
     
  17. Jun 8, 2006 #16

    pervect

    User Avatar
    Staff Emeritus
    Science Advisor

    I agree totally. The chemical energy in coal and oil is just that - chemical energy. It was present before the plant material was buried.
     
  18. Jun 8, 2006 #17
    i would say yes
    if youre not sweating (overheated)
    the cool food would cause your body temperature to lower slightly, which your brain would sense. your brain would then tell your body to heat up, using up energy.
    the thing is though, that eating hot food when youre already hot, might cause you to lose energy too, if not more. because then your body would have to expend energy sweating and replenishing that water
     
  19. Jun 8, 2006 #18
    Pervect

    Great question by the way. Its very creative and fun to think about.

    I think Pervect gave the correct answer.

    Since there is no way for the human body to extract energy from heat for use in metabolic pathways, the only difference that hot or cold food would make is how it would heat or cool your body's core temperature. For this reason, as pervect pointed out, eating hot food in the arctic would save you energy as you would need to expend less energy conserving body heat. However, eating hot food in the Sahara desert would cause you to sweat more which (i'm speculating here) would make you expend a minute amount of energy in the form of opening your sweat glands to cool down. Not to mention dehydration of course.

    Incidentally, the body metabolizes carbohydrates and extracts useful energy from them by means of the Citric acid cycle. Wherein, several chemicals are used (ie. water, Acetyl CoA, Hydrogen Phosphate, Hydroxyl ions, etc.) to transfer a Phosphate molecule around between ATP and ADP. IF the temperature at which the various reactions take place within the Citric acid cycle were elevated due to 'hot food', I would think that these reactions would occur quicker since their activation energies would be higher.
     
  20. Jun 9, 2006 #19
    Some nice biology there. On food packets, they label the nutritional value of the food, the first one is usually energy. Obviously heated food have more energy than cold food. For example, consider heating a glass of milk (400ml) for a minute in a 1000W microwave oven. A total of 60kJ would have been transfered to the milk after it has been heated. The milk contains a total of 1100kJ before heating, now it contains 1160kJ. That is a small extra amount of energy but still energy which may be valuable in some circumstances. Imaging heating the milk for 10 minutes. That would be 600kJ of extra energy - which is more than half of the milk's chemical energy. But you are claiming that our body does not metabolise heat energy. So no matter how hot the milk is, we cannot gain those extra energy in the molecules - which can be substantial for extremely hot food. Moreoever, the extremely hot milk probably will hurt the cells in our body causing the cells in our body to repair them which will cost us energy as many of already pointed out.

    Imagine a time when you are very hungary and there is a large pot of boiling water on the stove. I can imagine that no matter how much of it you drink, you will still be hungary afterwards. 2 litres of boiling hot water should have 836kJ of thermal energy in it. But your body can't extract that 836kJ can it? Your body will probably spend much more energy managing all this water.
     
  21. Jun 9, 2006 #20
    In that case, engines should work just as well when fed live plants?

    Why is there so much more energy in fossil fuel than recently dead plants? What is this 'extra' energy in the fossils if it is not chemical energy? How is it stored in fossils?
     
    Last edited: Jun 9, 2006
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?