# Drinking blood

There’s some interesting information on the caloric content of various blood components here. I haven’t tried to verify these figures independently, but since the poster appears to be a medical doctor I’ll take these at face value.

[Note that there seems to be an error in the calculation in step 2, in which he calculates blood plasma to be about 40% of the total volume, when if the hematocrit is 40% the plasma should be 60% of the sample. I have corrected for this in the figures below. Also note that he is using a female hematocrit of about 40%; for males it would be closer to 50%.)

Recalculating based on this error, according to these figures a liter of blood will provide:

0.5 gm glucose
182 gm protein (including both plasma and blood cells)
3.6 gm fat

The caloric value of a liter of blood will be 744 kcal.

Assuming a male needs about 2700 kcal a day, he will have to consume about 3.6 liters of blood daily, containing 655 gm of protein. That’s more than 10 times the recommended daily intake of protein for males (about 56 gm according to some sources).

That’s going to cause you big problems if your only source of water is that in the blood itself. I don’t think there will be enough to flush out all the urea and uric acid produced.

According to this site, one result of a high protein diet is water loss.

Another factor to consider is the concentration of vitamins and other essential nutrients in the blood. It might be necessary to consume even greater volumes of blood to acquire enough vitamins if they are at low concentration.

Unless you are a vampire bat with special physiological adaptations, it seems a blood diet would be very problematic especially due to the very high levels of protein that would needed to be ingested relative to the water available.

No, I’m disputing that a person can stay adequately hydrated by drinking isotonic fluid and excreting isotonic urine.

To start from the beginning, what I’m saying is this: Think about a day that’s cold enough to see your breath. What exactly is that cloud you’re seeing? Condensed water vapor, right? And it come from your lungs, which can only get the water from your bloodstream. So, it’s clear, I hope, that the body loses water through the lungs.

This isn’t just a trace, it’s actually a physiologically significant amount of water – wikipedia says 500-800 ml/day (for respiration and perspiration), compared to 1500 ml/day lost in urine – and the respiration loss is basically pure water, since it’s lost as vapor.

So therefore, simple mass balance says that drinking 2000 ml/day of fluid isotonic to blood, respiring 500 ml/day of pure water, and excreting via urine 1500 ml/day of fluid isotonic to blood will lead to a net gain of salt (the amount of salt in 500 ml).

Now, I know that in fact, the kidneys do concentrate salt (when necessary), and therefore urine is not always isotonic to blood. The question is whether the kidneys can concentrate it enough. Now to get rid of the excess salt for a fluid isotonic to blood, they only need to concentrate it by a factor of around 1.3 (they need to get rid of 2000ml worth of salt in 1500 ml of urine), so I’m pretty sure that in fact they can. But that’s not completely obvious from first principles, especially as we know that the kidneys do have a limit on how much they can concentrate salt – seawater provides too much salt for the kidneys to get rid of, even though that only requires concentrating the salt by a factor of 4 or so.

To recap: I think that you could handle blood as a food and liquid source, salt-wise, but only because the kidneys can concentrate salt. On the other hand, **colibri’**s work shows that calories vs protein might be an issue (though I don’t know if the body will stop absorbing protein at some point).

If it did that, you would have trouble making the calories up from elsewhere. About 97% of the calories available from blood are contained in the protein. To get your daily caloric requirement from blood lipids would require consumption of about 85 liters, or the entire blood supply of 17 people.

In high protein diets, like bodybuilding diets, blood intake proves superior to milk intake simply due to it has a greater protein/fat ratio. High iron content also boosts efficiency of oxygen transport from your lungs to any cell of your body. So if you can’t afford it or your wife doesn’t like the idea don’t invent excuses without actual data. I don’t say you could/must live only on blood, but its one of the greatest foods out there reserved only to successfull predators. The only consideration is to drink blood always from an opposite gender body than yours.

this is a neat fact.

Would liver be the organ best matching these requirements?

gm?

Gram.

This thread was started two and a half years ago, incidentally.

And for the record, neither blood type nor the gender of the donor would make the slightest bit of difference.

Damnit!

What’s with all these zombies floating to the surface recently? It never used to be like this.

OK, I’ll bite. (heh) Why?

I wish someone with more 'puter savvy would run the numbers. I’ve been here 8 years, and it seems like it’s always been like this. Maybe a bit worse since Google infested us with their spiders, but that was a couple of years ago now, right?

I have been away for a while (4 or 5 years, I think) and I don’t remember it being like this way back when. But this is probably the fifth zombie I have posted in without realising in the space of a week.

Even barring iron overload and salt content, what about nutrients that the body needs which don’t make it until the blood? There must be some vitamins and minerals that anyone surviving on blood long-term would be deficient in.

And scavengers. And hemovores like vampire bats, leeches, ticks and fleas.

You have research backing this or any other statement you’ve made?

I highly doubt that blood would be better than milk (this site claims it is one of the best post-workout drinks, note also that there is such a thing as skim milk, if the fat concerns you) since you also need carbohydrates for effective recovery and blood has very little carbs, and really WAY to much protein; there is no need for more than 1 gram per pound of bodyweight even in the most extreme cases (never mind bodybuilders cramming themselves with hundreds of grams of protein, much of which is just turned into glucose and fat, along with all of the metabolic waste which stresses the body).

Plus all of that iron can’t possibly be good for you; red blood cells are 97% hemoglobin by dry weight, so that would add up fast with even small amounts (the RDA is only 18 mg (men actually only need 8 mg a day), with 45 mg being the tolerable upper intake). Those other animals mentioned no doubt have adaptations to deal with all of that iron.

Worst combination of user name / post content ever?

Didn’t Mangetout try fried semen in the interest of the Straight Dope? I don’t mean to cast calumnies, but when I first began with GQ I was fantastically impressed. Perhaps it’s just username projection.

Rescuing Mangetout’s reputation - it was mangeorge

Si