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Some people say that it's awful that humans eat animals. They feel that it's barbaric, because you're killing life and then on top of that, you're eating it, and that you should eat vegetation instead.

But isn't vegetation life too? Personally, I see no difference between animals and veg as all life has cells, dna etc

So my question is, is it possible for humans to live healthy long lives without eating any type of life, i.e no animals, no plants, no cells (dead or alive) etc? If it is possible, how would it be done?

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closed as off-topic by Bez, Chris, The Last Word, MattDMo, WYSIWYG Aug 29 at 6:53

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based on your definition of life, yes! –  Bez Aug 21 at 13:53
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You mean on a strictly vegan based diet? No, that is not possible as we are not able to synthesize many important factors as Vitamin B12. There is no vegetable source for it. –  Chris Aug 21 at 14:01
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What about eating things that have died without you directly or indirectly having killed them? E.g. a fruit on its own is not alive and if you remove the seeds and plant them you are in no way killing anything. –  AndroidPenguin Aug 21 at 14:10
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@oshirowanen just remembered this (bbc.co.uk/news/science-environment-16972761) but I do not know if that falls in your definition of life and killing the living. –  Bez Aug 21 at 16:13
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The vague definition of life and intangible solutions presented makes the question and any solution offered highly speculative and philosophical in nature, deviating from any practical solutions or biology. –  Bez Aug 22 at 14:42

11 Answers 11

up vote 49 down vote accepted

The answer to your question is yes it is certainly possible.

At one time it was thought that there was something special about "organic" chemicals which meant that they could not be artificially synthesised out of fundamental elements. In 1828 Frederick Wöhler synthesised urea (CO(NH2)2) which is often taken as the first demonstration that the organic v inorganic distinction was not a sound one (for more on this see the Wikipedia article on Wöhler synthesis.

As far as we know all essential human nutrients can be synthesised from inorganic ingredients, even complex molecules such as Vitamin B12.

Other contributors have pointed out that organic pathways for synthesising our food have evolved over long periods to be very efficient - at least in the conditions prevailing on Earth. You haven't ruled out copying biochemical pathways using chemicals that are entirely of inorganic origin. Anyone trying to do this seriously could create glucose (for example) by artificially creating enzymes (perhaps via artificial DNA) to do the job. The thing is that we already have self-replicating and repairing machines to do that already (plants).

There might be circumstances when we needed to use artificial synthesis. I can think of two science-fiction stories that deal with this question, the first of which goes into some detail:

  • The Moon is Hell by John W. Campbell, in which astronauts are stranded on the moon and forced to make food from what they find there.
  • Technical Error by Arthur C. Clarke, in which a man is accidentally rotated through the fourth dimension. His employers contemplate the difficulty caused by the "handedness" of many biological molecules meaning they would have to artificially synthesise many of his foods.

It may be that a future expedition to Mars (say) might have to think about these things.

A little searching fails to come up with standard inorganic syntheses of glucose and similar substances. The reason for this is almost certainly because it is so easy to use organic inputs. Glucose is easily made by the hydrolysis of starch. Starch is very common and cheap. Even l-glucose is usually made out of organically derived precursors (or sometimes even using d-glucose).

UPDATE: sources etc One problematic question is: where do you get your input for making nutrients? As others have pointed out, exactly where to draw the line is difficult.

This problem starts in defining what is alive in the first place. Do you count viruses (which can go down to a few thousand base pairs of RNA) or satellite viruses (STobRV has only 359 base pairs) or prions? In a sense these are "just" very large molecules. But then really simple bacteria are not many orders of magnitude more complex. As an aside most systems of ethics that do not permit eating meat do not make an alive/non-alive distinction, choosing some other aspect such as sentience, though Jainism comes close to doing so.

The second problem is, if we reject living things as sources of food, how far removed from those living things are we allowed to get? You say no cells in any state including "dead". That would exclude (say) fruit even though most fruits are expressly created by plants in order to be eaten (and in some cases must be eaten) - something that vegans, jains, fruitarians and others would be happy with eating. If we could use dead material things would be much easier.

But would you also include hydrocarbons (coal, oil, gas) which were once living organisms? If you do, then you are in difficulty because terrestrial carbon is recycled through the biosphere. All CO2 was (to a close approximation) once a part of a living thing. If you take that position then of course you are going to have to go off-planet to find your source chemicals and your problem becomes very much harder.

I was assuming that you were restricting yourself to consuming cells that retain some of their cell structure but had not completely degraded. If that is where you draw the line then there are ample sources of raw materials on earth.

Genetic modification is much more science fiction though not entirely impossible. Some nutrients could be made by humans without much difficulty. Our inability to manufacture vitamin C is down to one missing enzyme (L-gulono-gamma-lactone oxidase) which is present in most vertebrates (I think of mammals only guinea pigs, humans and some bats are unable to synthesise it). You could certainly imagine some very careful genetic modification changing humans so they no longer need to consume vitamin C.

But photosynthesis would be much harder. Chloroplasts (which do the job in most plants) are really a very primitive form of life living in plant cells which may independently reproduce (and for that reason might be excluded by you - they aren't "cells" but they have membranes). They could easily end up in conflict with our mitochondria (since intracellular conflict between organelles is possible) and you would need to do enormous amounts of work to make human cells co-operate with them properly.

More in keeping with your theme would be adding photosynthetic systems directly to human cells along with a suite of enzymes to manufacture all the things we cannot. That is of course in principle scientifically possible (since plants do it) but much harder than it looks. Living systems are very complicated and small changes can have unexpected consequences. Even very minor genetic modifications are problematic. The human autotroph is likely to be some way off.

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+1 for the Asimov story! It is possible to survive on poisons only if one can rotate oneself through a fourth spatial dimension. I must also mention "Technical Error" (aka "The Reversed Man") by Clarke. –  Fixed Point Aug 21 at 22:23
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A "yes" would indicate that it would be possible right now. Do we have readily available technology for it available now? I guess not. Wouldn't that make a "No, but theoretically possible in the future"? –  vsz Aug 22 at 6:09
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Just to understand better: say we have set up a laboratory to inorganically synthesise every necessary nutrient. What would we use as raw materials? Where would we get carbon and the other elements? Would we able to obtain them without violating the OP's provisos? –  DaG Aug 22 at 8:12
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Did you mean to say, "most fruits are expressly created in order to be eaten ... by the plant", or did you actually mean "most fruits are created by the plant expressly in order to be eaten"? +1 for considering the variety of angles. –  Wayne Werner Aug 22 at 14:31
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Interestingly the GM to restore Vitamin C production has already been tried: sciencedirect.com/science/article/pii/S0888754303002714 –  Francis Davey Aug 22 at 16:02

Living organisms can be divided into hetrotrophs and autotrophs. Autotrophs like plants and algae are able to produce complex organic compounds from relatively simple inorganic components. They are satisfied with sunlight, water and other abiotic stuff and do not need to consume "life".

We -- along with all other animals -- are not autotrophs, but heterotrophs. This means that we cannot produce organic compounds by ourselves but need to 'reuse' the ones that are produced by autotrophic organisms. That's why no human will ever be able to live without consuming other life.

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Ever? Are you sure about that? –  antonone Aug 21 at 15:45
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As user137 pointed out, you would need to synthesize ALL nutrients from anorganic sources. No one will ever do this because plants have had hundreds of millions years time to become really really good in that. Why would you want to compete with them? In so far: Yep...never ever. –  Hav0k Aug 21 at 15:55
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organic != life. vultures? bacteria that decay matter? organisms consuming milk, eggs, fruit, pollen? –  AAA Aug 21 at 16:30
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This answer is wrong. As explained by @FrancisDavey, it is certainly possible for us to synthesise every single nutrient we need from inorganic substances, at the expense of energy which we can gain non-organically too for example through solar or nuclear sources. That is, by all ways of understanding it, "without eating any type of life". –  Armatus Aug 21 at 19:07
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Following this logic, you would have to answer almost every question with "yes, it's possible". Can we travel between solar systems at warp speed? No, but some people imagine it to be possible at some point far, far in the future. But based on our current knowledge that's fiction and does not mean anything. My answer is based our current knowledge, too. At the moment and in all foreseeable future it will not be possible to live without consuming 'life' (as defined by oshirowanen). I doubt it ever will... –  Hav0k Aug 21 at 20:01

Even on a purely synthetic diet, your body would still use living cells as an energy source. Our bodies contain more bacterial cells than human, mostly contained in our gut. These microbes process any nutrients we ingest and when they die, we absorb their cellular components as nutrition.

The lining of the gut is the most rapidly dividing population of cells in the body. Unlike skin cells, when these die, our intestines recycle much of this as nutrition. Throughout the rest of our bodies, when a cell dies, its components are recycled: red and white blood cells, mucosal membranes, invading microbes, etc.

When you kiss, engage in intercourse, there's also an exchange of living cells which die in the process.

Abstaining from organic food, human contact will not stop the fundamental processes of autophagy, apoptosis, digestion, cell turnover of both our own and microbial cells.

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The most beautiful answer. –  Aleksandr Dubinsky Aug 22 at 4:37
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Human solid body waste is as much as 50% dead bacteria from the gut. –  user2338816 Aug 22 at 9:50

Your question is phrased somewhat ambiguously as to whether you're asking about the theoretical possibility, the feasibility, or the practical ability in everyday life.

1) Theoretically, yes. It is chemically possible to produce all substances that humans need to survive without the use of living organisms in the process. In the end, biological systems use chemical processes, so at the very least it would be possible to isolate the biological (enzymatic) machinery and use it without the live organism around it. The latter is within current biotechnological capabilities.

2) Feasibly, no. Going through the hassle of making all those substances in that way would probably be less efficient than simply using the biological (live) systems that already exist and are very efficient at it - in particular, plants.

3) Practically, no. Using only currently commercially available products (i.e. things you could buy right now), you will probably not be able to source a full human diet without relying on some live organism at some point in its production exactly because of number (2) above.

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So now we agree. –  Hav0k Aug 22 at 9:14
    
I don't think we ever disagreed XD I felt like number 1) in my answer was what the question asked and so that would be the correct answer - but it's true that the question is sort of ambiguous and hence I decided to post this general answer. –  Armatus Aug 22 at 9:22
    
mattkaeo's answer provides an interesting additional consideration for (1), though. I don't know whether it's clear what happens when you stop "eating" your symbiotic gut flora. One might suppose that if all the necessary nutrients get into the bloodstream somehow then you're good to go, but there's probably more to deal with than just synthesizing the nutrients, since various systems in and around the digestive tract will be perturbed and need sorting. People fed entirely IV tend to be fairly unhealthy, admittedly they're usually unhealthy to start with, that's why they're fed by IV. –  Steve Jessop Aug 22 at 17:56
    
As long as the necessary nutrients are consumed orally and go through digestion, your gut flora and your own health should be fine. You could synthesise and consume indigestible carbohydrates (i.e. fibre) to support that additionally. His answer is an interesting thought though and does answer the question "Can humans survive without consuming life?" in a different angle. –  Armatus Aug 22 at 19:00
    
@SteveJessop there have been experiments on animals, rising them in a bacteria-free environment and thus without gut flora. ncbi.nlm.nih.gov/pmc/articles/PMC1500832 for example. The current verdict seems to be that this is possible, but unhealthy; if we ever would raise humans in sterile environment (interplanetary colonisation by growing people from fertilized cells and local resources?) then we should 'infect' them with the common gut bacteria. –  Peteris Aug 22 at 20:31

Depends on how you define "life"? Is unfertilized chicken eggs alive?

What about cow milk? Well there are bacteria in it. What if you get rid of that bacteria? Then some people would not be able to utilize lactose...

Also as Bez mentioned rice grains are quiescent, meaning they are in a dormant state and not really "alive" but again depends on how you define "life". Even top biologist have trouble defining "life" and there exist many competing definitions of "life". All of them have their advantages and disadvantages, but there is no universal definition of life on which all biologists would agree.

If you consider everything above as "life" then it is not really possible for humans to survive without consuming other life.

If only we could sustain chloroplasts in our epidermis layer we would be able to synthesize sugars for ourselves. But then we would become little green men...

So it is much better to respect your meat. Whenever you eat meat just be conscious that something had to die to produce that meat. Be grateful for that lost life and realize that part of it will live in you.

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Ask you asked, my definition of life is something has cells/dna in any form (dead, dormant, or alive). –  oshirowanen Aug 22 at 13:41
    
Viruses have DNA/RNA in them yet they are not living, they are more like containers. So not everything that has DNA is actually life. You can have a bunch of DNA in a tube, you wouldn't consider it life would you? –  N0ir Aug 22 at 15:33

Question: Is it possible for humans to live healthy long lives without eating any type of life, i.e no animals, no plants?

First, according to a definition of a living organism(biology-online), milk is not live, because it does not have an ability to reproduce itself, among other...

My claim: If you consider milk and honey non-live (no DNA), then, yes, humans can survive for some time by consuming only these, and water. An example are infants, who can live exclusively on human breast milk and water for more than 1 year.

This is human milk composition (Nutritiondata), from which you can see it contains all essential nutrients (Nutrientsreview) (essential amino acids, fatty acids, vitamins and probably all essential minerals - not all essential minerals are listed in Nutritiondata milk composition, though).

But to actually prove that humans can or cannot "live healthy long lives" by consuming only milk and honey, one would need to do a human trial...and I'm not aware of any.

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I think if you live off the by-product of a creature that consumes life, it would be cheating to claim that you don't. –  Aleksandr Dubinsky Aug 22 at 4:45
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You do not need to kill or harm a living being to use its milk. I believe, from what is obvious to me, this is how things are meant to be, at least for infants. –  Jan Aug 22 at 6:27
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And how will the cow produce its milk? It has to graze, therefore killing thousands of organisms. –  Boluc Papuccuoglu Aug 22 at 11:03

No.

It is possible but extraordinarily impractical to nourish yourself without killing animals, plants or even bacteria, as many have explained in detail.

However, your immune system constantly kills pathogens that infect your body. What's worse, the macrophages literally catch and eat these bacteria alive, so you are very much "consuming" them.

You could live in a bubble, but even then there are bacteria in your gut. In your gut, they are not attacked by your immune system, but they can sometimes get through the gut lining into the body, where they are attacked. They could also escape from you anus into the environment, and then end up elsewhere in your body.

Even if you had a magic force field keeping the gut flora inside the space of your intestinal lumen, they could still mutate and become immunogenic, then get consumed by your macrophages. Anyhow, collectively, your gut flora has more cells than your body, so is it really fair to say "you" did not consume any life when this symbiotic bacterial mass living inside you (more like you are the parasite living outside it) consumes some of its own cells?

But let's say you get rid of your gut flora, too. It's a hell of a life, and you wouldn't wish it on your enemy, but it solves that problem. Now only human cells are present inside your bubble. What happens when eventually your cells mutate and you get cancer? There are natural killer cells that will try to consume the cancer. So you have still consumed life.

Let's say you made yourself immune to cancer. That's impossible, but let's say you made your DNA polymerase so high fidelity that it takes millions of years for even a single mutation to occur (this is also almost impossible). Your body still has to kill cells through apoptosis as part of maintaining its own function. Again, to conserve resources, these cells are literally swallowed. It's debatable whether an apoptotic cell is alive, but it is made to die by influence of other cells, so this is very analogous to killing a chicken and eating it. In principle.

The answer is no, but your question becomes meaningless if you define "life" scientifically. It is only possible to live without consuming life if "life" means only plantae, metazoa and fungi. But that is not what it means, because at least some Eastern religions do consider eating microbes to be "consuming life".


Lame, boring answer

The Universe has a finite reserve of (dis)entropy. When that runs out, no more life can exist, because all life must increase entropy. Even on Earth, by simply being alive you are taking up space that could be used by other organisms. To be alive you require some form of energy; even if this energy is solar, you would still be using up energy that could have been used by a plant.

By simply existing, you are irreversibly destroying vital resources necessary for other life. Thanks to you, at least some life somewhere will be left without resources and starve. Therefore you cannot exist without harming life.

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It may be feasible to live without consuming anything that was alive, but it would be incredible difficult.

For example, all humans need to consume glucose to survive. Glucose is the only food source used by cells in the brain. Plants are the easiest source of food source for glucose. If we can't get glucose from plants, then we would need to synthesize it without the aid of enzymes or any sort of organism. A quick google search does not yield any hits for how this synthesis could be performed. Probably because it is so easy to get a plant to make the sugars for us.

Now think about all the amino acids, vitamins, fats, and minerals that we would also need to synthesize or extract without any organism intervention.

You have gone from the good intention of not harming another organism to the creation of a whole chemical industry dedicated to the production of nutrients for people.

Think about this as well. When you poop, a lot of the poop is actually dead bacteria that was living in your gut.

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Can you please improve your answer and add some references? If you want to know about glucose synthsis in the human body, look up gluconeogenesis. –  Chris Aug 21 at 16:06
    
It would be great if you could add references to your answer specially regarding the last line! –  Bez Aug 21 at 16:06
    
@Chris Gluconeogenesis is how your body generates glucose as a last resort. It is a lot easier just to eat glucose. It requires the use of enzymes. I suppose you could synthesize the enzymes in vitro. –  alex Aug 21 at 16:09
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"When you poop, a lot of the poop is actually dead bacteria that was living in your gut." Some of them are still alive... imagine their horror... Now all vegetarians are gonna stop pooping –  N0ir Aug 21 at 16:31
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@N0ir As John Lennon put it "Imagine there's no heaven..." –  TomD Aug 21 at 16:34

Well, technically if you are eating something from a plant or animal without killing that plant or animal, then technically you would not be "consuming life" as nothing as been killed. Fruits, for example, can be removed from the tree without harming it and in fact are meant to be removed as that is how the tree reproduces. Ditto with berries, melons, squash, cucumbers, peppers, beans, seeds, nuts, etc.

As for animal products I think only milk and honey would qualify as technically an egg is a future animal.

So yes, I would say that it is completely possible to live a healthy life without once killing another living thing.

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As far as I understand, fruits are alive, they have cells and dna just like animals and humans. A single cell is a simple form of life. So if you're eating fruit, technically, you're consuming life. Therefore, no different from eating an animal. If you think about it on a larger scale, you could say that animals are the fruit of the earth... –  oshirowanen Aug 22 at 8:23
    
There is no way you could go through life without EVER consuming something with cells. Even while you are sleeping several hundred ants, insects, spiders, etc WILL crawl into your mouth and be swallowed over your lifetime. Why the problem with consuming cells, anyway? Fruits and the like will fall off and decompose anyway and they are not sentient, so why the moral dilemma? –  Peramia Aug 22 at 8:39
    
Ah, I see. Then I suppose it's theoretically possible to survive without INTENTIONALLY consuming living cells, but great scientific effort would have to go into making the synthetic products available –  Peramia Aug 22 at 8:44
    
@oshirowanen if you count even single cells as alive, then that includes bacteria and other single-celled organisms that aren't even plants. Such a diet isn't currently feasible, for some key nutrients the only vegan options are obtained by killing bacteria. –  Peteris Aug 22 at 20:35

It is entirely possible to live without consuming life using only current technology. In fact, there is a company called Soylent which has developed a food substituent designed to replace all eating, entirely. The philosophy of that company is that – food is just a collection of chemicals for the body to process, and that as long as the body gets all of the necessary chemicals, it will survive fine. That is exactly what soylent aims to do – the powdered mix they produced has all the chemicals necessary for human life.

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The ingredients in Soylent get its calorific value from rice, oats, soy and other plant products. As such it doesn't fulfil the criteria of the question asker –  Rory M Aug 21 at 20:01
    
Soylent Green is People! –  DaG Aug 22 at 8:15

Honey is produced from nectar that does not contain any living cells and carefull beekeeper should be able to take at least some from the hive without killing any bees. However bees themselves will also consume pollen that is alive.

It also may be possible to feed on fruits; while cells there are still alive, they are about to die soon without any prospects of future surviving. If you really do not want to harm the plant in any way, take the seed from the fruit and plant it somewhere. Fruits are for seed propagation only and the plant should really not have any pretensions to you afterwards.

Dead leaves in the autumn may contain the needed materials; unfortunately they are not edible directly and would need some pre-processing technology.

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