How much energy do our bodies use to keep warm?

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Posted: Mon Jul 09, 2007 5:04 am

Dear font of all things wise and wonderful (that means you, all you 419eaters),

A simple question that I am sure some knowlegeable person can answer (mrs bean, are you there?). Can anybody tell me how much energy energy our bodies burn to keep warm when the weather is cold? For example our bodies should be around 37degC nornmally. When it gets cold, but before we get to the shivering stage, our body starts to burn fat to keep warm, or so I am told. How much does it try to burn if it is say 15degC and where are used to 22degC?

No, I'm not trying to lose weight by standing outside in the middle of winter, just rather curious.

Posted: Mon Jul 09, 2007 5:10 am

I'm no expert, but isn't a calorie the amount of energy required to heat one gram of water one degree C. I think that would be the basis for the formula. I know there is an answer to your question, I just don't have it. I guess I'm just post whoring. sorry.

Posted: Mon Jul 09, 2007 5:11 am

Just a guess.
It takes 1 cal to raise 1 gram of water 1 degree C. Your body is about 80% water. Take 80% of your weight and multiply by the number of degrees you need to raise your body temp. It would not be accurate since your normal temperature is core temp and not surface temp. Probably an over estimate.
There are charts to calculate the amount to latent heat a body gives off when you calculate the amount of air conditioning power you need to cool a room. That may give a better estimate but it would be a normal output and not related to increasing the amount of energy your body has to burn to increase its temperature.
The two may give you a feel for the range.

Also here is something to get you thinking
http://www.newton.dep.anl.gov/askasci/zoo00/zoo00094.htm

Oh and also I remember that 1 calorie in science is equal to 1 kilo-calorie of food, IIRC. So you have to adjust for that.

Posted: Mon Jul 09, 2007 7:26 am

I guess your body must use up energy to stay warm quite a lot, considering that one of the main reasons reptiles don't need to eat as often as mammals is because they don't need to maintain a warm body temperature.

However, it's not really the kind of thing you would think of a tiring you out, and also it doesn't seem as though people in cold countries are any less likely to be overweight than those in hotter countries... if anything the opposite might be true.

Are you trying to justify answering "keeping warm" when someone asks "what exercise have you been doing lately?"

Posted: Mon Jul 09, 2007 7:51 am

This falls into the topic of human thermoregulation, which I studied very briefly. As I'm sure you know, there are a number of things to take into account. When your body reacts to a low external temperature, it does the following things:

-Your body hair will stand up to trap heat at the skin surface.
-Your heart slows down and arteries/capillaries will tighten to keep warm blood near the vital organs.
-Breathing will slow down, also to conserve heat.
- Sweat glands and pores will tighten up.

Interestingly, none of these things burn much more energy than "normal" conditions demand. It's only when shivering starts that extra energy is burned, or when you voluntarily exert yourself to keep warm. Also, there are a number of factors to consider. What the subject human is wearing, their metabolism, their individual "comfort levels", and about a dozen other things will all have an impact on the correct answer.

While all of the above tidbits are documented facts, I still don't have a friggin clue what the answer you're looking for really is. I just wanted to sound intelligent, so I answered a question with more questions. If university-types can do it, then so can I!

Posted: Mon Jul 09, 2007 2:15 pm

callum wrote:

A simple question that I am sure some knowlegeable person can answer (mrs bean, are you there?). Can anybody tell me how much energy energy our bodies burn to keep warm when the weather is cold?

I would think metabolism calculations would be of some help, but there are so many factors involved, it wouldn't be all that simple... From what I can find, metabolism is usually expressed as the number of calories burned over time.

Your personal BMR would factor in. Problem is, BMR also includes the energy it takes to keep your organs going, etc, besides body temperature. But an estimated 10% of that energy supposedly goes to body temperature regulation.

http://en.wikipedia.org/wiki/Basal_metabolic_rate

You can apparently get a rough estimate of that based on age, sex, height and weight, though.

Here's the non-metric version. There's a link for an Excel spreadsheet.

http://www.weight-loss-lose-weight.com/basal-metabolic-rate-calculator.htm

Then you would also have to factor in surface area of the person's body. I haven't a clue how you would measure that from a practical point of view...

So, in other words, research suggests it's bleeding complicated, and at best, you're going to get a guesstimation. I think you have to visit people with white coats and electrodes and clipboards for a real answer.

I got 1320 calories for my BMR. So, presumably, in a typical day, I would use about 132 calories maintaining my body temperature under normal conditions. By the way, holy shiznit, the Excel spreadsheet says I must typically burn 2047 calories a day. No wonder I'm eating like a lumberjack.

So the answer is obviously 42. On account of quantum.

Posted: Mon Jul 09, 2007 11:01 pm

mrsbean wrote:

Then you would also have to factor in surface area of the person's body. I haven't a clue how you would measure that from a practical point of view...

But I'm sure the formula would include a variable for bra size Laughing

yrubraj wrote:

Are you trying to justify answering "keeping warm" when someone asks "what exercise have you been doing lately?"

Good point. See, cat's aren't so lazy after all!

Thanks all!

Posted: Mon Jul 09, 2007 11:14 pm

Try this for some relevant info, although I cannot vouch for its accuracy. I did hear tell of a man who lost a lot of weight by sleeping every night with the window open and no covers through the winter, but I cannot find anything to back that up or disprove it. Sad

Posted: Mon Jul 09, 2007 11:20 pm

Even if you lose a bit of weight, I don't think getting pneumonia is particularly good for one's health.

Posted: Tue Jul 10, 2007 12:16 pm

Eight wrote:

I did hear tell of a man who lost a lot of weight by sleeping every night with the window open and no covers through the winter, but I cannot find anything to back that up or disprove it. Sad

On a similar note to that Eight, it is possible to expediate one's weight loss by drinking large volumes of cold water throughout the day. Not only is it good to flush out the system, but the body expends heat to warm up that cold water.

Posted: Tue Jul 10, 2007 2:43 pm

^^^^^^

Although be careful not to overdo that as drinking too much water can over-dilute the blood - potentially leading to death.... Sad

Posted: Tue Jul 10, 2007 4:08 pm

yrubraj wrote:

Even if you lose a bit of weight, I don't think getting pneumonia is particularly good for one's health.

That's how he lost the weight. Hospital food.

(But as I always point out to my granny, germs and viruses make you sick, not being out in cold/damp weather. They've done studies 'n' such on whether being wet and cold made you more prone to being ill. Didn't. Oddly, exercising really hard does...)

I've heard the "cold water" thing, too, but I would think that would be a very negligible gain over just drinking plenty of water in general. But hey, every little bit helps. At the very least, you get plenty of walking in while making trips to the restroom.

Posted: Tue Jul 10, 2007 9:37 pm

I'd heard that too, jojo. Does the same apply if you chill your chocolate bar first? Smile

Posted: Wed Jul 11, 2007 12:55 pm

Don't ask me, I am over 200 lbs. But since you pointed it out, every time I go to buy a Snickers, I'll get the ones they put in the freezer.

I am inclined to agree with you Mrs. Bean; the energy used by your body is minimal from just drinking cold water. But that does seem to be a very common tactic. I will say, however, a common survival tip is that if you are stranded in a snowy area, that you should always melt snow before using it for water. This is so you don't use up your body's heat/energy. So, maybe there is SOME level of validation to it.

Again, I am neither a survivalist or a nutritionist. I just keep on an extra layer of padding in case I am ever stranded.

Posted: Wed Jul 11, 2007 3:17 pm

Great question.

One thing about that warming up 1 degree/ gram thing. That's a calorie. Not at Calorie. Things you eat are orders of magnitude larger. A kilocalorie.

Check it out yourself for heating effects. Take a Dorito. Set it on fire in a safe location. Check out the heat given off. Now do the same remotely in a oxygen rich container in a water bath. Measure the change in temperature. You've made a bomb calorimeter and can see that it could change more than 10 grams of water 1 degree Celsius.

If I were going to measure calories burned at 15 degrees vs 25 degrees I would go with determining oxygen consumption.

One of the reasons that you don't want to eat ice/snow in a survival mode is that the enzymes that your body uses in metabolism are tuned to working at 37 degrees. Once your core temp goes below that, the rates of reaction go way down. After a while its really hard for your body to generate enough heat and bad things happen.

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