# Composition of Human Blood? **URL:** \ **Category:** Factual Questions\ **Created:** [April 13, 2010, 9:51pm UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990 "2010-04-13T21:51:42Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Teddy\_P](https://avatars.discourse-cdn.com/v4/letter/t/df705f/32.png) [@Teddy\_P](https://boards.straightdope.com/u/Teddy_P)\ **Post date:** [April 13, 2010, 9:51pm UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/1 "2010-04-13T21:51:42Z")
So I donated a pint the other day and joked with the phlebotomist that the Red Cross ought to advertise this as the quickest, no-fail way to lose a pound. That got both of us to thinking. So I donated a pound (or so) in mass, but how many additional calories did I lose with the protein and whatnot in the blood itself? Oh, great, now I’m wondering what the nutrition label would look like for vampire chow…🙂 ---
**Author:** ![chrisk](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@chrisk](https://boards.straightdope.com/u/chrisk)\ **Post date:** [April 13, 2010, 11:01pm UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/2 "2010-04-13T23:01:21Z")
Well, I think the amount of nutrients (sugars, fats, protein) in your bloodstream varies quite dramatically, mostly based on whether you’re digesting a meal or not. Exercise could have an effect too. Based on this blog entry: [http://www.blog.sethroberts.net/2008/02/28/how-many-calories-are-in-your-blood/](http://www.blog.sethroberts.net/2008/02/28/how-many-calories-are-in-your-blood/) , there was maybe half a gram of blood glucose in that pint you donated - or around 2 calories worth (conversion here - [How many calories are released when 1 gram of glucose is completely broken down in the presence of oxygen? - Answers](http://wiki.answers.com/Q/How_many_calories_are_released_when_1_gram_of_glucose_is_completely_broken_down_in_the_presence_of_oxygen) ) And it seems like the red blood cells don’t take ‘much’ energy to form. (reference here [http://iplmatchhighlights.com/biology-forum/about1296.html](http://iplmatchhighlights.com/biology-forum/about1296.html) ) I couldn’t find any quantitative figures though. Bottom line - that pound was mostly water, and we all know how quickly your system will regain THAT. 😉 ---
**Author:** ![toodlepip](https://avatars.discourse-cdn.com/v4/letter/t/97f17d/32.png) [@toodlepip](https://boards.straightdope.com/u/toodlepip)\ **Post date:** [April 13, 2010, 11:09pm UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/3 "2010-04-13T23:09:00Z")
[Cecil’s covered this already,](http://www.straightdope.com/columns/read/2441/can-i-donate-blood-to-lose-weight) sort of. His source says: > [@](#): > > Taking into account the composition and energy in each component . . . I estimated that one unit of blood reflects about 600 cal of food intake. I don’t know how this was worked out. A rough calculation based on the composition of cow’s blood - dry matter content around 20%, almost all of which is protein, with a tiny amount of fat and carbohydrates - gives me a figure of 385 kcal per 500 ml. [This](http://www.fitbit.com/foods/Lamb+Blood/7287) nutritional info on lamb’s blood seems to fit with that, at 375 kcal per 500 ml. (Should have just googled it before bothering to do my own calculations!) Finally, in [a more complicated calculation](http://www.madsci.org/posts/archives/aug99/935553476.Me.r.html), human blood comes out at 341.4 kcal per 500 ml. ---
**Author:** ![Hirka\_T\_Bawa](https://avatars.discourse-cdn.com/v4/letter/h/db5fbb/32.png) [@Hirka\_T\_Bawa](https://boards.straightdope.com/u/Hirka_T_Bawa)\ **Post date:** [April 13, 2010, 11:51pm UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/4 "2010-04-13T23:51:23Z")
I actually asked this question a few years ago. Here is the old [thread](http://boards.straightdope.com/sdmb/showthread.php?t=398043&highlight=blood+calories), it has some good posts. ---
**Author:** ![Qwakkeddup](https://avatars.discourse-cdn.com/v4/letter/q/90ced4/32.png) [@Qwakkeddup](https://boards.straightdope.com/u/Qwakkeddup)\ **Post date:** [April 14, 2010, 2:01am UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/5 "2010-04-14T02:01:02Z")
> [@Teddy\_P](#): > > So I donated a pint the other day and joked with the phlebotomist that the Red Cross ought to advertise this as the quickest, no-fail way to lose a pound. That got both of us to thinking. So I donated a pound (or so) in mass, but how many additional calories did I lose with the protein and whatnot in the blood itself? > > Oh, great, now I’m wondering what the nutrition label would look like for vampire chow…🙂 Well, at least you did mention vampires, cause I read the title as **Consumption** of human blood…:smack: ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [April 14, 2010, 2:18am UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/6 "2010-04-14T02:18:14Z")
Here’s the original source: > [@Quoting myself quoting myself](#): > > About six hundred. > > Quote: > Transfusion Medicine > Volume 11 Issue 5 Page 390 - October 2001 > doi:10.1046/j.1365-3148.2001.00328-2.x > Six hundred reasons to donate blood > > D. A. Redelmeier > > I walked back from an economics lecture, passed an advertisement for a weight-loss clinic, and arrived at my appointment to donate blood. A thought came to mind: why does a rational economist ever donate blood? The activity takes time, requires planning, involves transportation, causes pain, and indirectly leads to lost personal productivity. Additionally, some risk of financial cost is assumed if sloppy application of the disinfectant causes a bad clothing stain. > > I then had an idea. Perhaps blood donation could be promoted as one way to lose a bit of unwanted weight. Taking into account the composition and energy in each component (Rechcigl, 1978; Kratz et al., 1998), I estimated that one unit of blood reflects about 600 cal of food intake. Hence, a single donation can off-set either 2 hamburgers, 3 donuts, or 5 granola bars. Awareness of these statistics might increase the appeal of blood donation, particularly among healthy adults who are concerned about obesity. > > References > > • Rechcipl, M. [ed.] (1978) CRC Handbook Series in Nutrition and Food Section E Nutritional Disorders, Vol II. CRC Press Inc., p402. > > • Kratz, A., Kent, B., Lewandrowski, K.B. (1998) Case Records of the Massachusetts General Hospital (Normal Reference Laboratory Values). New England Journal of Medicine, 339, 10631072. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [April 15, 2010, 2:46am UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/7 "2010-04-15T02:46:55Z")
> [@toodlepip](#): > > [Cecil’s covered this already,](http://www.straightdope.com/columns/read/2441/can-i-donate-blood-to-lose-weight) sort of. His source says: > > I don’t know how this was worked out. A rough calculation based on the composition of cow’s blood - dry matter content around 20%, almost all of which is protein, with a tiny amount of fat and carbohydrates - gives me a figure of 385 kcal per 500 ml. [This](http://www.fitbit.com/foods/Lamb+Blood/7287) nutritional info on lamb’s blood seems to fit with that, at 375 kcal per 500 ml. (Should have just googled it before bothering to do my own calculations!) Finally, in [a more complicated calculation](http://www.madsci.org/posts/archives/aug99/935553476.Me.r.html), human blood comes out at 341.4 kcal per 500 ml. Yes but the calorific value of the blood is going to be lower than the energy it takes to _form_ it. The components (amino acids etc.) from the food have to synthesized into the right human proteins, lipids, and so forth that make up human blood plasma and red and white cells. That takes energy. ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [April 15, 2010, 2:57am UTC](https://boards.straightdope.com/t/composition-of-human-blood/535990/8 "2010-04-15T02:57:18Z")
> [@njtt](#): > > Yes but the calorific value of the blood is going to be lower than the energy it takes to _form_ it. The components (amino acids etc.) from the food have to synthesized into the right human proteins, lipids, and so forth that make up human blood plasma and red and white cells. That takes energy. Plus a lot of material is thrown away during the development of red blood cells, in particular the _entire nucleus_. It costs a fair amount of energy to replicate DNA, and it’s all thrown away, along with all sorts of associated proteins and such. Now I’m sure the body reuses all the molecular building blocks it can, but the energy used to synthesize these components is lost.