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There are many differences in for example the digestive system between carnivores, herbivores and omnivores.

It seems that in certain kinds of species adaptability with respect to diet is possible. What I have heard is that it is impossible for carnivores to survive on a non-meat diet.

Therefore I wanted to ask: Is it really impossible for a carnivore to survive on a vegetarian diet, even when the fruits/vegetables/plants are processed? I could see how their digestive tract would not allow for them to survive on grass, but what about certain kinds of nuts, mushrooms, or even processed plant based foods?

If it is impossible to survive on these diets, why?(With respect to either causes in their digestive system or substantial differences between meats and any type of vegetarian food.

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    $\begingroup$ I think this is too broad - "carnivores" is a large and loose group of species that range from obligate to facultative carnivores, and the answer to your question is likely to depend on exactly what species your are talking about. $\endgroup$ – fileunderwater Jun 9 '15 at 8:31
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    $\begingroup$ Thank you very much for this specification. I am talking about species which are categorized under obligate carnivores. $\endgroup$ – St.Clair Bij Jun 9 '15 at 20:31
  • $\begingroup$ This would be a great question here: area51.stackexchange.com/proposals/94068/veganism-vegetarianism $\endgroup$ – Attilio Dec 8 '16 at 18:47
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With arbitrarily broad meaning of "processed", yes. If absolutely nothing else, elemental purification and inorganic synthesis of something chemically resembling meat in nutrition is possible. Prohibitively expensive and stupid, yes, but possible. So then the question becomes exactly how much processing you need to do. Without clear bounds on that question and inadequate research on the metabolism of obligate carnivores, nothing closer than a broad stab at an answer makes sense. That said, here's a broad stab.

For instance, you'd probably need to synthesize vitamin D3, carnosine, DHA, and a handful of other things from plant extract, which is possible but difficult. Carnivores often have carnosine synthases, for instance. Cats have two distinct carnosine synthases. In terms of dietary sufficiency, that may or may not be enough. To be sure, you'd have to break it down to amino acids and build it back up again, essentially. Obligate carnivores are likely to have a number of other metabolic needs that aren't met with, for instance, pulverized soybeans. You're going to need at least one vat for fermenting raw amino acids into carnosine, and probably another for vitamin D3. Seawater microalgae contain lots of DHA, so that is probably something to look into. You could oversupplement alpha-linolenic acid instead of supplementing DHA, which might or might not work. There's not a lot of study into carnivore metabolism, so prepare to make some discoveries the hard way. Genetic studies can only take you so far, so don't try this on your favorite pet first.

In short: yes, you can raise carnivores on a diet made from plants and plant material. Rhetorical you, as in it is possible. It's probably not something you can do at home, even if you're wealthy.

(I'm assuming "feeding the vegetable matter to chickens" falls outside the domain of "processed" but it would be much easier than large-scale amino acid purification and fermentation.)

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    $\begingroup$ I would rephrase this to be "No, not without synthesizing certain essential nutrients not found in plants". Otherwise you might as well say that you could also feed carnivores on a diet of "processed" air, water, and dirt. $\endgroup$ – augurar Jun 9 '15 at 4:47
  • $\begingroup$ Thank you very much for your answer. As I understood it is normal that carnosine is synthesized within animals by a natural process involving beta-alanine and histidine. (In humans the enzymes, which carnivores may lack, will decompose the carnosine into beta-alanine and histidine when taken into the mouth in that form). $\endgroup$ – St.Clair Bij Jun 9 '15 at 8:09
  • $\begingroup$ Vitamin D3, in humans is not taken in as such. It is mostly vitamin D activated by the kidney and the liver. Where hydroxyl groups are added to activate it. One of the groups is the carbon 25 through the liver and the other carbon 1. This leads to the most active form of vitamin D= 1 25-dihydroxyvitamin d3. Is it for carnivores, like humans, the case that this vitamin must be processed in their own bodies to be useful? If so, would they need meat, unlike humans, to get enough of this vitamin? (It seems that mushrooms that have been exposed to ultraviolet b light contain high lvls vitamine d. $\endgroup$ – St.Clair Bij Jun 9 '15 at 8:20
  • $\begingroup$ Calvo MS, Garthoff LH, Feeney MJ, et al. "Light exposed mushrooms: From development to market of naturally enhanced plant sources of vitamin D." Proceedings of the 5th International Congress on Vegetarian Nutrition. Loma Linda, CA; March, 2008. $\endgroup$ – St.Clair Bij Jun 9 '15 at 8:20
  • $\begingroup$ As for DHA (And EPA) That seems like a workable idea! (That is if their digestive system would allow to process it) (Which I would not know why it wouldn't) $\endgroup$ – St.Clair Bij Jun 9 '15 at 8:26
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Of course it is possible for a carnivore to live with a vegetarian diet. Technically you could come up with a complete meal out of vegetables and make a carnivore pup live with it. Dogs and cats are good example of it. They can learn to eat vegi-processed food and as far the nutrients needed are present they will grow and live well. To make them eat raw vegetables is more difficult.

As correctly asked by the commenters, here some links where you can find some info about:

Vitamin D3 in plants (many thinks that only meat/fish contains it)

Carnosine also can be synthesise by the body, here the main references

DHA that is contained in several veg food

Vitamin B12 from cyanobacteria

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    $\begingroup$ I'm not sure this answer is factually accurate. For example: dogs and cats differ in their ability to synthesize taurine, an otherwise essential amino acid. Synthetic taurine is cheap, but it's not possible to feed a cat "a complete meal out of vegetables" without adding certain nutrients. $\endgroup$ – Resonating Jun 8 '15 at 18:59
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    $\begingroup$ Nope, the answer is wrong when it stays this general. We cannot synthesize certain important vitamins (B12 for example) and there is not plant source for it. $\endgroup$ – Chris Jun 8 '15 at 19:49
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    $\begingroup$ @Chris, vitamin B12 is present in lots of vegetables, here a small list of them healthaliciousness.com/articles/… $\endgroup$ – alec_djinn Jun 9 '15 at 7:13
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    $\begingroup$ @Resonating: taurine is not an amino acid. It does not even have a carboxylate group. It is an amino alkyl sulphonic acid $\endgroup$ – WYSIWYG Jun 9 '15 at 7:29
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    $\begingroup$ @alec_djinn I am talking about B12, not B2, as you linked. If you look on the relevant list, you will see that all the B12 there is derived from animals (meat, milk, eggs...). $\endgroup$ – Chris Jun 9 '15 at 7:29

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