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This question: Can you get enough water by eating only fish? asks if a person could survive on fish alone. Can a person survive on fish and/ or blood alone of any species if stuck at sea or animal blood as a last resort where there is no water or fire?

Obviously if it was a fresh water fish there is water, but there are fresh water mud skippers that can breathe air and the water to tainted to drink in that case a fresh water fish blood maybe safer than the water. https://chemistry.stackexchange.com/questions/115901/what-can-i-eat-that-will-help-metabolize-blood

Desalination would be the best way to process the blood but this is in emergency situation scenario.

From @PTwr Comment's Link: If you drink blood regularly, over a long period of time the buildup of iron in your system can cause iron overload. This syndrome, which sometimes affects people who have repeated blood transfusions, is one of the few conditions for which the correct treatment is bloodletting. https://what-if.xkcd.com/98/

Muze
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4 Answers4

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Blood is not a good source of water.

1 liter of blood contains about 800 mL of water, 170 grams of protein and 2 grams of sodium (calculated from the composition of lamb blood).

When metabolized, 170 grams of protein yields the amount of urea that requires 1,360 mL of water to be excreted in urine (calculated from here); 2 grams of sodium requires about 140 mL of water to be excreted (from here).

This means that drinking 1 liter of blood, which contains 800 mL of water, will result in 1,500 mL of water loss through the kidneys, which will leave you with 700 mL of negative water balance.

Fish blood can contain less protein, for example, trout (check Table 1) contains about 120 g of protein (plasma protein + hemoglobin) per liter of blood. Using the same calculation as above (1 g protein results in the excretion of 8 mL of urine), drinking of 1 liter of trout blood, which contains about 880 mL of water, will result in 960 mL of urine, so in 80 mL of negative water balance.

Turtle blood can contain about 80 g of protein (plasma protein + hemoglobin) and 3.4 g of sodium per liter. Drinking 1 liter of turtle blood, which contains about 920 mL of water, will result in 80 x 8 mL = 640 mL loss of urine due to protein, and ~240 mL due to sodium, which is 880 mL of urine in total. This leaves you with 40 mL of positive water balance (to get 2 liters of water per day you would need to drink 50 liters of turtle blood, which isn't realistic.

In various stories (The Atlantic, The Diplomat, The Telegraph), according to which people have survived by drinking turtle blood, they have also drunk rainwater, so we can't conclude it was turtle blood that helped them. I'm not aware of any story that would provide a convincing evidence that the blood of turtle or any other animal is hydrating.

Community
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Jan
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    I think this answer addresses the main reasons. The iron issue may be a long term problem but most single foods will cause long term problems if one tries to feed on them exclusivley. – Peter - Reinstate Monica May 22 '19 at 14:22
  • Assuming a sufficient supply, could you drink a lot of blood and eventually get to a point where the protein is no longer metabolized? – Flater May 23 '19 at 11:19
  • Normally, protein does not accumulate in your body, so it is metabolized even if you consume it in excess. Excessive protein is mainly converted to body fat. – Jan May 23 '19 at 12:18
  • Wouldn't a dehydrated body stop even picking up the protein from the small intestine and only absorb water? (just a guess) This also doesn't get rid of the sodium problem, but that is not so severe.. – Martin Modrák May 23 '19 at 13:50
  • Protein absorption would stop only in severe dehydration. As long the water is absorbed, the protein will likely be absorbed too. – Jan May 23 '19 at 13:53
  • Question revised. – Muze May 24 '19 at 16:46
  • Blood of what, not all blood is the same. fish blood can vary quite a lot in protein composition.however it is true that all the reported cases of drinking fish blood for survival also included capturing rain water, fish blood being used to stretch water not as a complete replacement. – John May 25 '19 at 03:56
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You can drink blood of course to a minimalistic amount (eg- a few teaspoons ) and also if blood is free from pathogens. But it should always be in very small amounts and from suitable donor. Here's why

The strange fact is, blood, when drank, is toxic. When confined to places where blood is supposed to be — such as the heart, vessels, and so on — it is essential for life. But when ingested it's a very different story.

Now why is it even harmful?

  1. Haemochromatosis- this is a disease where your body has excess iron/ iron overdose which gets deposited in organs such as heart, liver , pancreas etc. This happens because blood is very much rich in iron but our body doesn't have any suitable mechanism to excrete the excess iron. (There is some doubt with the actual cause of Haemochromatosis. It is a disease related to iron overdose but its not sure whether the main cause is genetic or it can be anything related to diet as well.)

  2. Blood related disorders, eg :- AIDS, Hepatitis B etc - If blood is not taken from a suitable donor or the equipments you use to take it in are not sterilised properly, you'll probably contract one of these disorders, which are absolutely life threatening.

  3. Malnutrition- Although blood contains 93% proteins and 1% carbs , blood is terribly low in minerals and vitamins.

So basically blood taken in small amounts will have no harm on you, but you surely can't survive on blood.

For the sources, visit - https://www.livescience.com/15899-drinking-blood-safe.html

https://www.sciencefocus.com/the-human-body/could-i-live-as-a-vampire-by-just-drinking-blood/

https://medicalxpress.com/news/2018-04-bad-blood.html

Ishi
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  • Could you please cite your references? Who made the statement you're quoting? – Arsak May 22 '19 at 05:18
  • @Arsak This whole answer has been taken from multiple sources, but the one i quoted is from https://www.livescience.com/15899-drinking-blood-safe.html – Ishi May 22 '19 at 05:44
  • You should add this and the other sources to your post. It would surely improve your answer. – Arsak May 22 '19 at 05:57
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    @Arsak thankyou so much for the suggestion, I have added the sources. – Ishi May 22 '19 at 06:03
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    Haemochromatosis is a genetic disorder found in those of European descent, and common among those with Irish descent. It has nothing to do with drinking blood, but involves a variant chemistry for white blood cells. – Pieter Geerkens May 22 '19 at 11:34
  • @PieterGeerkens Please check out this link https://www.livescience.com/15899-drinking-blood-safe.html I also checked onto this, and the defination is coming the same you are referring to. But maybe there are two sides to this, or maybe I am wrong. Anyways, please check onto this link and let me know about what's right. – Ishi May 22 '19 at 11:50
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    @Ishi: The author is a writer and editor, not a scientist: "Benjamin Radford is deputy editor of Skeptical Inquirer science magazine and author of six books including Scientific Paranormal Investigation: How to Solve Unexplained Mysteries." Absence actual scientific evidence, this article is not worth the paper it was written on. – Pieter Geerkens May 22 '19 at 11:53
  • @PieterGeerkens thankyou so much for giving me the correct information, I'll immediately remove it from the answer as I don't want any ambiguity in the OP's mind. – Ishi May 22 '19 at 11:56
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    @PieterGeerkens I'm pretty sure haemochromatosis is too much iron, regardless of the cause. The genetic disorder is just the common cause, but it's still called haemochromatosis if it's dietary. – JMac May 22 '19 at 11:57
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    @JMac: Haemochromatosis is specifically too much ferritin, a particular iron compound used by the body to dispose of iron. This disposition is done through elimination of the white blood cells that create ferritin. Thinking that haemochromatosis is too much iron kills people - like my dad, whose physician refused to listen to experts such as Paul Adams: Honorary Fellowship for Distinction - Royal College of Physicians of Ireland 2013. You are thinking of iron overload, the generic syndrome. – Pieter Geerkens May 22 '19 at 17:39
  • @PieterGeerkens It seems like the definitions are themselves highly inconsistent. Some places refer to hereditary haemochromatosis as just haemochromatosis, where you will find other sources which consider iron overload to be a form of haemochromatosis that is non-hereditary. – JMac May 22 '19 at 17:56
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    It's very difficult to be infected by HIV orally. – forest May 22 '19 at 19:04
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    #2 and #3 don't seem particularly relevant. Yes, you can contract blood-borne diseases by drinking blood, but you can also contract water-borne diseases by drinking water. The fact that some blood is infected with disease doesn't make it an unsuitable replacement for water. And water contains no vitamins, and single-digit %DV of many minerals, depending on the source - I don't see how you could become malnourished by replacing part of your diet that has marginal nutritional value to begin with. – Nuclear Hoagie May 22 '19 at 19:34
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    @PieterGeerkens Seems like they're not much of an editor, either, saying "when drank" rather than "when drunk". – Acccumulation May 22 '19 at 20:08
  • @forest And usually more fun than drinking blood. Well. Depends on one's inclinations, I suppose. – Peter - Reinstate Monica May 24 '19 at 10:17
  • sorry to -1, but the few teaspoons are too far off the mark. Upper Daily Intake, i.e. daily iron intake that is tolerable long term for healthy people without being likely to lead to health issues according to NIH (https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/) is about 45 mg. Calculating with 500 mg Fe/l blood (http://www.jbc.org/content/104/1/157.full.pdf - that's human, didn't find fish info) and 15 - 35 % absorption (https://academic.oup.com/ajcn/article/91/5/1461S/4597424) means that UDI is reached somewhere between 250 and 600 ml blood per day. That's 50 - 120 teaspoons. – cbeleites unhappy with SX May 24 '19 at 11:45
  • Acute trouble from too much iron occurs at > 20 mg/kg body weight (NIH). That would be around 8 l blood. And then, that trouble is mainly gastro-instestinal, not iron-storage/ferritin related. (I'm assuming that anyone with hereditary hematochromatosis will immediately discard the "solution" in OPs question. Just as anyone with fish allergy would.) – cbeleites unhappy with SX May 24 '19 at 11:45
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    Also, note that (cow/zebu) blood is a major part of traditional Maasai diet (https://en.wikipedia.org/wiki/Maasai_people#Diet) - which is just one ethnicity among many who eat blood (and liver) sausages (https://en.wikipedia.org/wiki/Blood_sausage). Coming from a blood and liver sausage region, I can say that a serving blood sausage in a hot main meal (lunch/dinner) may be ≈ 150 - 200 g or 50 - 130 g blood ≈ 25 - 60 mg Fe (liver: 15 mg/serving). Main health concern here is usually not iron intake but lipids. (Anyways these traditional meals that are not eaten daily) – cbeleites unhappy with SX May 24 '19 at 12:36
  • @cbeleites don't they drink water and have any other food? Because i'm here exclusively talking about "surviving on blood" – Ishi May 24 '19 at 12:49
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    Ishi: of course they do (so do the "vampires" in your links). As @Jan's answer points out everyone has to: the protein content alone means that humans (and many carnivores) need additional water. Any amount of blood does increase thirst instead of quenching it. I should have been more precise and stated that my comments are concerned with your point 1 (2 and 3 already being taken care of by Nuclear Wang). Thus, I consider your answer to give 3 bad reasons against drinking blood while omitting the relevant one. – cbeleites unhappy with SX May 24 '19 at 13:33
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    @cbeleites some fish lack hemoglobin entirely so iron levels are very low. – John May 25 '19 at 04:00
  • Bonus question? – Muze May 29 '19 at 16:36
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Here is a specific account of a person surviving at sea drinking turtle blood, while eating some fish and drinking some rain water.

Several peoples have a habit of drinking raw animal blood, at least for ritual purposes; here is a recent account. They probably drink more than a few spoons full so that the Lifescience article quoted by Ishi appears alarmist.

Peter - Reinstate Monica
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    It is very unlikely that blood from any animal, including turtles, will be hydrating and we can't just rely on a story. – Jan May 22 '19 at 14:46
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    @Jan Well, obviously it depends on how much water you ingest from other sources, and perhaps even on the food (because there is metabolic water). The body will also adapt to not having enough water (perhaps even by using stress metabolic pathways, like excreting uric acid?); the numbers found are surely the optimal, healthy ones. Apparently, blood is a net water drain under normal conditions, but whether that holds if there is little water overall is not immediately clear to me. – Peter - Reinstate Monica May 22 '19 at 15:09
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    @Jan I also find refuting concrete evidence with "we can't just rely on a story" unsatisfying. What is science if not the collection and interpretation of stories? Of course ideally stories which have been intentionally and carefully produced, but stories nonetheless. – Peter - Reinstate Monica May 22 '19 at 15:11
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    The first source you linked says that "We're not sure just how long you can survive off turtle blood, but Ivan did say that he was also drinking rainwater." We do not know the amount of rainwater he drank, so we cannot conclude that drinking turtle's blood helped. We can rely on stories and learn from them, when they clearly say what exactly happened, but we do not know this here. – Jan May 22 '19 at 15:14
  • Very informative and the answer could then be yes indefinitely. – Muze May 23 '19 at 22:30
  • @Muze Careful (that's why I didn't agree with your edit): I think Jan has a point. While blood is nutritious (which may have helped the survivor) it may indeed remove water from the body when it metabolizes the protein. That water must be ingested in addition to the minimum amount without blood. But it's also possible that when dehydrated the body can metabolize the protein through different pathways, or with less water, or simply excretes excess protein, but I could not find anything about it. – Peter - Reinstate Monica May 24 '19 at 05:32
  • In the intestine, macronutrients (carbohydrates, fats and proteins) are usually completely or nearly completely absorbed. You can't hope your intestine will filter out protein and absorb only water. It is possible that intestine does not absorb all the protein when ingested in great amounts - in this case it will trigger diarrhea with a great loss of water. – Jan May 24 '19 at 08:37
  • @Jan That makes sense; but perhaps it could be removed from the blood (and be excreted) without metabolizing it? I read that it is a sign of kidney desease to have protein in the urine, but that would make sense under dehydration which stresses the kidneys. It could even be a sign for damage (due to dehydration) but still lead to more available water. – Peter - Reinstate Monica May 24 '19 at 10:08
  • Excessive protein (amino acids) enters the cells, where it is converted mainly to fat - this process yields nitrogen, which is removed from the body via urine in the form of urea, which drags some water with it. So, it is exactly this "protein removal" that causes dehydration. In healthy people, unmetabolized protein is not excreted into the urine or otherwise and, in short-term, cannot be stored somewhere in the body in great amounts. – Jan May 24 '19 at 10:27
  • @Jan comments are temporary and these comments would be relevant in your answer. – Muze Jun 02 '19 at 19:31
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You'd have no problem substituting blood for water, provided:

  1. You allowed it to coagulate first, and
  2. You prevented it from evaporating

Fresh blood has a high concentration of protein, certainly, but it's not a homogeneous fluid. If you decanted the blood into a container and let it sit, it would soon coagulate, causing the majority of the cellular and protein components to precipitate and stratify.

The plasma fraction (approximately 55% in healthy mammals, and not radically different in most species with hemoglobin) forms a supernatant (the top, easily accessible layer) which is 95% pure water by volume and about 5% protein.

The sodium salt concentration of plasma is about 140 mEq/L, or 3.2 g per L (mEq = mg / atomic weight * valence, Online Calculator). Since healthy kidneys can concentrate salt to 4-5X osmolality (and since the source material is physiologic blood), you'd have no problem drinking the top, liquid portion. You would also avoid most of the long term iron issues as the hemoglobin is found in the erythrocyte (deposited) fraction.

Thirsty vampires will be disappointed that plasma appears amber, not "blood red"

Kvothe
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  • @Jan, total osmolality for blood plasma is 275-300 mOsm/kg - see https://www.sciencedirect.com/topics/medicine-and-dentistry/plasma-osmolality for a reference. This encompasses salts, glucose and soluble proteins. – Kvothe Jun 06 '19 at 19:37
  • @Jan, not clear what you mean by net water. If you take a 1 L blood volume, 55% of that (the plasma) is 550 mL. Is that what you mean? – Kvothe Jun 06 '19 at 19:38
  • @Jan - I'm not sure the back and forth is helpful, but I think you're missing that the kidneys serve to actively concentrate fluid. Remember, your kidneys are actively concentrating your entire blood plasma volume about 60 times per day (which just like the orally consumed plasma is about 300 mOsm/L). Kidney input is 300 mOsm/L, and output can go to 1500 mOsm/L. For example, the original WHO Oral Rehydration Solution was 311 mOsm/L WHO ORS and rehydrates. Also the "protein" in plasma is predominantly urea already. – Kvothe Jun 07 '19 at 21:14
  • @Kvohte, urea needs to be removed from the blood by urine. Consumption of 25 g protein (5% of protein in 500 mL of plasma) will result in 25 x 8 = 200 mL of urine, because 1 gram of protein results in the amount of urea that needs 8 mL of water to be excreted ( nap.edu/read/10925/chapter/6#135 ). This means that by drinking 500 mL of water from plasma, you get only 300 mL of net water because the urea will force 200 mL of it out into the urine. Do you agree with this? So, plasma would be still hydrating, but not as much as it seems. I need to think about sodium effect a bit more. – Jan Jun 08 '19 at 10:30
  • Can't believe this question was accepted, blood literally kills you if you drink it... –  May 19 '20 at 23:01