The following question was asked on Quora (first in the OP about drinking human blood, and later in the comments about drinking animal blood)
> Would human blood be a healthy drink for humans? Not that I want to try
Ian York (Virologist, immunologist, biologist) answers on Quora:
> Human blood would be a terrible drink for humans. Not only would it have an excellent chance of spreading disease, it has very little nutrition and contains toxic components.
> I think the disease concern is obvious. Any blood-borne disease (hepatitis C, hepatitis B, HIV, many more) would have the potential for spreading this way.
> As for nutrition, blood is mostly liquid. If we look to vampire bats to see how they manage, we see that vampires drink over half their weight at each 30-minute meal . They manage this by rapidly absorbing the nutritive parts of the blood and peeing away the rest . Humans aren't able to do either of these -- the rapid absorption and the rapid urination are both specific adaptations -- so humans would have a hard time getting much nutrition from blood.
> Then there's the toxicity issue. Blood is very rich in iron, obviously, and iron is very toxic. (Iron poisoning is one of the more common toxicities in children.) Again, vampire bats have specific adaptations to deal with this ("The common vampire bat maintains iron balance by severely limiting the percentage of iron absorbed from its very high iron diet" ). Humans trying to get enough nutrition from blood would poison themselves with iron.
*Update to add: Quora User asked in comments if the same applies to animal blood too*
> With animal blood, there's much less concern about blood-borne pathogens, so let's look at the toxicity. There's a huge range of concentrations at which iron can be toxic, depending heavily on the precise form of the iron (which affects how well it's taken up into the body). Since heme iron is taken up well, I'm going with a relatively low concentration of 10 mg/kg as an acute toxic dose . So let's say around 500 mg total (for a 50 kg person) would be getting into a dangerous range.
> Most of the "blood iron concentrations" you see are only serum concentrations, not counting hemoglobin, but some search turns up 50 mg per 100 ml of blood in whole blood of humans  and I will assume that's the ballpark for animals as well.
> That puts you into a danger zone with just a liter of blood (500 mg iron), which really isn't all that much.
> I don't know how much nutrition there is in blood, but I think it's fair to assume that it's significantly lower than milk (which is, of course, designed specifically to be nutritious). Drinking a liter of milk a day would certainly help with nutrition, but wouldn't be close to sufficient for most 50 kg people.
> So (TL;DR) it seems likely that even animal blood would be pushing the toxic envelope before it was a significant contribution to nutrition.
> What counterexamples come to mind? **It's widely known that Masaai, among others, mix cow blood with milk for a drink. But as far as I can tell this is mainly a ceremonial drink, not a daily staple; and though I can't find a recipe the blood is diluted into milk at least 50:50 and maybe quite a bit more**.
> Things like blood puddings and the like are other possible ways to ingest blood, but I have no idea how much volume of blood ends up getting ingested there
Dr. Joel Fuhrman has written an article about the misinformation being spread around the diet of the Inuit and the Maasai (posing their diets as an example of a long-term healthy diet):
This comment on the article, about the Maasai says it all for me:
> Barry Groves theory that we are actually carnivorous animals and more carnivorous than dogs and that plants are actually not necessary or suited for us is not one any of his collegues accept, in fact Weston Price himself would say Groves is hallucinated as Weston Price praised the virtues of vegetations, suggested a diet that was not high fat or low carb and suggested everyone to eat starch foods like grains, legumes or potatoes.
> But remind this when you want to know where Barry Groves is coming from: he believes we're carnivorous animals that thrive on a meat only diet, to him we're more like tigers and lions than primates
> This belief thought is not shared by low carb authors, paleo diet authors or traditional diet authors.
> **Masai and Inuits are two extremes examples. There are studies proving that Masai suffer from cardiocirculatory and neurologic disease (Masai are not immune to atheriosclerosis for example)** and their diet is rich enough in carbs not to be ketogenic and certainly not a carnivorous meat-only diet.
> There are evidences that Inuits adapted to an extreme diet in an extreme environment, that they have metabolic peculiarities and optimal for cold climate fat distribution and yet they have been suffering from liver enlargement and electrolytes deficiency
> Steffenson himself wrote that a 40 years old Inuit looked as old as a 70 year old American.
> **Talking about traditional hunter/gatherer populations, of all examples of traditional hunter/gatherer diets Groves took the two extremes as an ideal archetype. But the truth is that majority of hunter/gatherer diet are in the middle of the dietary spectrum consuming a balance of animal foods and plant foods**.
> For example the Bushmen consume a diet which is 75% plant food, their staple are nuts and they believe that there can't be health without plant foods while their animal food staple is fish
> **Not only the Bushmen are fit, healthy and strong but they're healthier than either Masai or Inuits**
> **So, one wonders why among the dozen of healthy hunter/gatherer populations that share a common health and dietary pattern with a big consumption of green, fruits, roots, tubers, nuts and plant food in general Groves based his idea of dietary perfection on just two isolated, extreme and not even ideal cases**
> Comment by Davide - May 5, 2006 4:31 AM