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, 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.
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 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, 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.
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.
