Calorific value of the typical person

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Calorific value of the typical person

Postby bentheimmigrant » Thu Jul 01, 2010 3:23 pm UTC

I think the subject pretty much sums up what I'm looking for. Various wordings of google searches were obscured by fuel energy densities and nutritional facts about various foodstuffs. So how much energy is there in the average cadaver (I suppose it's only right that the person being burnt/consumed should be dead). I'm actually thinking about calorific value in terms of fuel... I guess kJ/kg would be quite the satisfactory unit as it could be used for personal energy contents. However, if anyone knows of the useful (digestible) calorific contents of a person from a dietary perspective, I will be both disturbed and grateful.
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Re: Calorific value of the typical person

Postby Kow » Thu Jul 01, 2010 4:48 pm UTC

Well, if you know what their body fat % is and how much of the rest of their body is inedible (unless you're looking for the calorie count on those parts too), I'd imagine you could just figure it out by mass. ~3500 kcal is 1 lb of fat, or 9kcal to 1g of fat. 4kcal to 1g of protein or carbohydrate.
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Re: Calorific value of the typical person

Postby Velifer » Thu Jul 01, 2010 5:53 pm UTC

If the contents are as demented as the cover, you'll have an answer for $140!
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Re: Calorific value of the typical person

Postby EricH » Thu Jul 01, 2010 5:59 pm UTC

Let's see--for men, I'd estimate 42% muscle and 15% fat, so nutritionally that's (.42*4 + .15*9 = 3.03 calories/g); for women let's estimate 36% muscle, 20% fat, so (.36*4+.2*9=3.24); in other words, around 3000-3250 cal/kg. Higher if the cadaver is more obese. That may also neglect the organ meats, which are generally somewhat fatty tissues, but I don't know if they're included in body fat percentages. At least that gives you a floor for calculations.

Someone else will have to figure out the raw chemical energy available.

(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)
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Re: Calorific value of the typical person

Postby Velifer » Thu Jul 01, 2010 6:07 pm UTC

This is why we know so much more about animal nutrition than human nutrition. We can grind up various bits of animals at various life stages on various diets, or even toss a cow into an adiabatic bomb calorimeter. IRBs tend to frown on doing that with people. Another mammal might be a good proxy on calories per pound though.
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Re: Calorific value of the typical person

Postby BlackSails » Thu Jul 01, 2010 6:12 pm UTC

Velifer wrote:If the contents are as demented as the cover, you'll have an answer for $140!


Is that jamie from the mythbusters?

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Re: Calorific value of the typical person

Postby ++$_ » Thu Jul 01, 2010 6:44 pm UTC

Well, about 15% of the body weight is skeleton and perhaps 50+% is water (plus a little bit in the skeleton that we already counted), so you end up with 30-35% combustible material by mass. Let's just estimate that about 1/3 of that is fats and fatty acids (36 MJ/kg), and the rest is protein and carbohydrate (21 MJ/kg). Then you get an average of 26 MJ/kg of combustible material. But only 1/3 of the body mass is combustible, so the end result is 8-9 MJ/kg.

EDIT: Looking at Van Pelt et al, "Proximate composition and energy density of some north pacific forage fishes", it seems that the energy density of the dry mass ranges between 15 MJ/kg and 21 MJ/kg, with an outlier at 28 (the myctophid, which has a lot of fat). Their figures include bones, which is probably why they are mostly lower than mine. The fish have high water content, with most being near 80%, so their overall energy density is in the range of 2.3-5.7 MJ/kg. The myctophid also has an unusually low water content for a fish, with only 71%, so its energy density is 8 MJ/kg. People have less water than fish.

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Re: Calorific value of the typical person

Postby bentheimmigrant » Thu Jul 01, 2010 7:09 pm UTC

I forget sometimes how much I love these fora... Where else can you ask about such a thing and get a seriously considered answer?

With regard to the uncombustible contents of the body, spontaneous combustion cases often involve complete combustion, including bones (I assume the water boils off though)... So how much energy does that produce?
If we're looking at 8 MJ/kg, I may need to gain some weight... I'd like to measure myself in GJ.

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Re: Calorific value of the typical person

Postby Carnildo » Fri Jul 02, 2010 5:11 am UTC

EricH wrote:(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)

The answer to that is easy: no. An unmodified human body has an extremely high water content, and will not burn without an external source of heat.

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Re: Calorific value of the typical person

Postby bentheimmigrant » Fri Jul 02, 2010 9:43 am UTC

Carnildo wrote:
EricH wrote:(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)

The answer to that is easy: no. An unmodified human body has an extremely high water content, and will not burn without an external source of heat.


I'm not so sure about that... Once you get them going, it seems people keep burning if you do it slowly. I remember watching the program about this years ago - Yes, they used a fuel source to get it started, and clothing/blankets help to perpetuate it, but the body itself burns too.

So if we add an additional qualifier to that sentence, and allow for a clothed person to be burnt, with a bit of kerosene to get it going, can you cook a person with a person? (I suppose it's up to you if you prefer rare or well done, as this may be a deciding factor)
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Re: Calorific value of the typical person

Postby Velifer » Fri Jul 02, 2010 11:46 am UTC

++$_ wrote:fish.

They popped up in my cursory lit review too. Everyone seems to be running them through the Bassomatic. Fish are very different from mammals though, especially big fat McDonalds chowing humans. Ask gross anatomy students: people are made of huge globs of disgusting yellow fat, and then some other stuff that will be on the test.
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Re: Calorific value of the typical person

Postby Levelheaded » Fri Jul 02, 2010 12:16 pm UTC

EricH wrote:
(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)


It's certainly possible.

For example, in Egypt mummified bodies were common enough that they were used as fuel for fires. There are even apocryphical accounts that they were used as fuel for boilers on locomotives / steamships.

The things I've seen where non-mummified people have been set on fire usually require a substantial outside fuel source or a very obese person.

Anyway, how many calories are in a typical person?

Going on some standard percentages for typical / healthy humans, we get the below figures for men and women:
Women - 27% fat, 35% muscle, 12% skleton, 25% skin / blood / plasma / connective tissue / hair / etc.
Men - 15% fat, 45% muscle, 15% skeleton, 25% skin / blood / plasma / connective tissue / hair / etc.

I'm making the assumption that any nutrition (not specified if marrow is included in skeleton %) in the skeleton will make up for non-nutritous / indigestible mass in the 'other' category and ignoring the skeleton value.

Muscle is 75% water, fat / other is roughtly 50% water. The mass of a typical person with a nutritional value would be:
Woman - 14% fat + 9% muscle + 0% skeleton + 13% 'other' = 36%
Man - 8% fat + 11% muscle + 0% skeleton + 13% 'other' = 32%

Using Wikipedia for average weights, we find that the average American has :
Woman - 164 lb * 36% = 59.04 lb with nutritional value
Man - 191 lb * 32% = 61.12 lbs with nutritional value

I wasn't able to find the nutritional value of human or recommended serving size, but I'll assume the 'meat' above is prepared as jerky. Beef Jerky has about 116 calories / oz or 1856 calories / lb.

So my back of the envelope calculation shows that by preparing all of the edible portions of a human as jerky would give you:
Woman - 59.04 lb * 1856 calories / lb = 109,578 calories
Man - 61.12 lb * 1856 calories / lb = 113,439 calories

At a recommended 2000 calories / day, the average woman would give 55 days of food, the average man would give 57 days of food.

At 1200 calories / day (minimum number of calories for survival), the average woman would give 91 days of food, the average man would give 94 days of food.

So to simply survive, eating nothing but human, a cannibal would go through about four people per year. I would think they would need a supplement to get all the vitamins they need, but I'm not sure about that.

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Re: Calorific value of the typical person

Postby Alexius » Fri Jul 02, 2010 1:31 pm UTC

Levelheaded wrote:
EricH wrote:
(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)


It's certainly possible.

For example, in Egypt mummified bodies were common enough that they were used as fuel for fires. There are even apocryphical accounts that they were used as fuel for boilers on locomotives / steamships.

The word "mummy" comes from an Arabic word meaning "tar". Of course they'll burn- anything organic will burn if you dry it out and cover it in tar...

As for how to find this value, you could probably get a good estimate by looking up equivalent values for pigs, which are probably a lot easier to find.

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Re: Calorific value of the typical person

Postby quantropy » Fri Jul 02, 2010 5:23 pm UTC

I guess a really obese person might get up to 1 Planck energy

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Re: Calorific value of the typical person

Postby fooliam » Fri Jul 02, 2010 7:22 pm UTC

A "Typical" person (non-sex/nationality specific) is generally put at 154 lbs (70 kg) for purposes of calculating caloric expenditure, so I'm gonna use that (and because 70kg is easy to work with). We'll also use 21% body fat, as thats a good average if we're not being particular about the sex of this hypothetical person (15% if male, 27% if female). We don't have to worry about water weight, as that's accounted for in the 9kcal/g for fat, 4kcal/g muscle. We can assume that the skeleton has 0 caloric content, as it is mostly mineral. The average human skeleton accounts for ~15% of weight, or 10.5 kg in this case. So, the hypothetical average person has roughly 59.5kg worth of calorie-containing mass. Since some organs are very fatty (such as the brain) and others are very muscular (such as bladder), I'm going to just pretend they average each other out and are irrelevant to the overall body composition. so 21% of 59.5 is 12.495kg, which is the fat mass of this hypothetical person. Therefore, the lean or muscle mass would be 47.005kg.
So, we have 112,455kcal for fat mass. and 188,020 kcal for lean mass. Total caloric content would then be 300,475 kcal.

*it occurred to me that the total value will be slightly lower due to whatever the mass of connective tissue would be. I'm not sure about how much connective tissue a body would have (though not all that much...even a few pounds seems excessive), and I'm also not sure about the energy density of collagen (vast majority component of connective tissue). However, I don't think this would vastly alter the results or calculations.

*2nd edit -levelheaded's post made me realize I didn't account for blood - removing weight of blood (which we'll assume as water and calorie-free)...5L at a density of 1060kg/cubic meter...so 5.3kg worth of blood in our hypothetical person. take that 5.3 from the 59.5 for a total combustible mass of 54.2kg. Using the 21% fat, 79% lean...102,438 kcal of fat, 171,272 kcal of lean mass for a total caloric content 273,710 kcal. Or roughly 136 days of food at 2000 kcal (2000 Calories) a day.
Last edited by fooliam on Fri Jul 02, 2010 9:58 pm UTC, edited 2 times in total.
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Re: Calorific value of the typical person

Postby ++$_ » Fri Jul 02, 2010 9:02 pm UTC

fooliam wrote:We don't have to worry about water weight, as that's accounted for in the 9kcal/g for fat, 4kcal/g muscle.
Not so. For example, Wolfram Alpha gives a figure of 201 calories for 85 grams of beef.

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Re: Calorific value of the typical person

Postby fooliam » Fri Jul 02, 2010 9:17 pm UTC

++$_ wrote:
fooliam wrote:We don't have to worry about water weight, as that's accounted for in the 9kcal/g for fat, 4kcal/g muscle.
Not so. For example, Wolfram Alpha gives a figure of 201 calories for 85 grams of beef.


nutritional labels are subject to rounding error. there are actually 11.22 grams of fat in that 3 oz of beef (11.22 = 100.98, notice the "101 Calories from fat" on the upper right hand corner of the nutrional label.) The rounding error will also apply to the protein content and the carbohydrate content.

Oh, and you also have to remember that a nutritional Calorie is different from a calorie. 1 Calorie = 1000 calories. The capitalization matters

*edited because I originally misunderstood what you were trying to say.
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Re: Calorific value of the typical person

Postby fooliam » Fri Jul 02, 2010 9:27 pm UTC

Levelheaded wrote:
EricH wrote:
(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)


It's certainly possible.

For example, in Egypt mummified bodies were common enough that they were used as fuel for fires. There are even apocryphical accounts that they were used as fuel for boilers on locomotives / steamships.

The things I've seen where non-mummified people have been set on fire usually require a substantial outside fuel source or a very obese person.

Anyway, how many calories are in a typical person?

Going on some standard percentages for typical / healthy humans, we get the below figures for men and women:
Women - 27% fat, 35% muscle, 12% skleton, 25% skin / blood / plasma / connective tissue / hair / etc.
Men - 15% fat, 45% muscle, 15% skeleton, 25% skin / blood / plasma / connective tissue / hair / etc.

I'm making the assumption that any nutrition (not specified if marrow is included in skeleton %) in the skeleton will make up for non-nutritous / indigestible mass in the 'other' category and ignoring the skeleton value.

Muscle is 75% water, fat / other is roughtly 50% water. The mass of a typical person with a nutritional value would be:
Woman - 14% fat + 9% muscle + 0% skeleton + 13% 'other' = 36%
Man - 8% fat + 11% muscle + 0% skeleton + 13% 'other' = 32%

Using Wikipedia for average weights, we find that the average American has :
Woman - 164 lb * 36% = 59.04 lb with nutritional value
Man - 191 lb * 32% = 61.12 lbs with nutritional value

I wasn't able to find the nutritional value of human or recommended serving size, but I'll assume the 'meat' above is prepared as jerky. Beef Jerky has about 116 calories / oz or 1856 calories / lb.

So my back of the envelope calculation shows that by preparing all of the edible portions of a human as jerky would give you:
Woman - 59.04 lb * 1856 calories / lb = 109,578 calories
Man - 61.12 lb * 1856 calories / lb = 113,439 calories

At a recommended 2000 calories / day, the average woman would give 55 days of food, the average man would give 57 days of food.

At 1200 calories / day (minimum number of calories for survival), the average woman would give 91 days of food, the average man would give 94 days of food.

So to simply survive, eating nothing but human, a cannibal would go through about four people per year. I would think they would need a supplement to get all the vitamins they need, but I'm not sure about that.


The problem with your method of calculating total caloric content is that it doesn't take into account the differences in composition of jerky and people. Jerky is made from very lean meat typically. People are not very lean, so you're cutting out a lot of Calories by not taking all that fatty goodness into account. You're also assuming jerky is completely dehydrated, which it isn't.
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Re: Calorific value of the typical person

Postby ++$_ » Sat Jul 03, 2010 9:11 pm UTC

fooliam wrote:
++$_ wrote:
fooliam wrote:We don't have to worry about water weight, as that's accounted for in the 9kcal/g for fat, 4kcal/g muscle.
Not so. For example, Wolfram Alpha gives a figure of 201 calories for 85 grams of beef.


nutritional labels are subject to rounding error. there are actually 11.22 grams of fat in that 3 oz of beef (11.22 = 100.98, notice the "101 Calories from fat" on the upper right hand corner of the nutrional label.) The rounding error will also apply to the protein content and the carbohydrate content.

Oh, and you also have to remember that a nutritional Calorie is different from a calorie. 1 Calorie = 1000 calories. The capitalization matters

*edited because I originally misunderstood what you were trying to say.
It's still well below 4 kcal/g, no matter how you slice it. Especially if 101 of the Calories are from fat and there are 11 grams of fat, because then the remaining 74 grams (which is all muscular tissue, unless the beef has a bone in it, and even then it's at least 50% muscular tissue) accounts for only 100 kcal.

And sorry for not capitalizing the C.

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Re: Calorific value of the typical person

Postby gmalivuk » Sat Jul 03, 2010 10:49 pm UTC

fooliam wrote:
++$_ wrote:
fooliam wrote:We don't have to worry about water weight, as that's accounted for in the 9kcal/g for fat, 4kcal/g muscle.
Not so. For example, Wolfram Alpha gives a figure of 201 calories for 85 grams of beef.
nutritional labels are subject to rounding error. there are actually 11.22 grams of fat in that 3 oz of beef (11.22 = 100.98, notice the "101 Calories from fat" on the upper right hand corner of the nutrional label.) The rounding error will also apply to the protein content and the carbohydrate content.
I think you missed the point: that bit of beef averages out to less than 2.4kcal/g, which means your figures above are obviously leaving something out.
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Re: Calorific value of the typical person

Postby Jorpho » Mon Jul 05, 2010 2:33 am UTC

EricH wrote:(Surely cannibal tribes must know whether it's possible to cook a human by burning another human....)
Never mind cannibal tribes. Surely the proper place to look for information on this matter would be in crematorium research? If nothing else there are plenty of patents.

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Re: Calorific value of the typical person

Postby fooliam » Wed Jul 07, 2010 6:48 pm UTC

You are correct, I am wrong.

Also, I thought I'd add the following, just to further complicate things.

The 4kcal/g for carbohydrates and protein and 9 kcal/g for fats is based off work done by W.O. Atwater ~1900, and are rough averages. They are not completely accurate because different proteins have different amino acid compositions, and thus have different heats of combustion. So a food which is high in say...trytophan very possibly could have a significantly different protein energy density than a food which is high in say...myosin. So, without knowing the exact protein composition and the energy density of each of those proteins, you are going to have small errors in those calculations. And sometimes, these errors aren't so small. For example, the average energy density of protein in eggs is 4.36 kcal/g, while the average energy density the proteins in soybeans is 3.47 kcal/g. This same type of variability exists for fats and carbohydrates as well.
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