You've landed on another planet. There are some forms of plants and animals on this world but how do you know what is safe to eat?

Obviously we went through this on earth, finding the right berries and such that wouldn't make us ill but is there a better way than trial and error? A small crew wouldn't want to risk being without one of its members (either through illness or death).

In terms of their abilities they've the technology to make interstellar travel and survive that. Their ship does have the ability to grow a variety of foods so initially they're in no rush so we can have some tests which take a little longer. Imagine the technology as sufficiently advanced that if we've identified something today that it could be testable.

This question is about a team of qualified people, chosen for an interstellar trip. In this question solutions are for an individual stranded in a life or death situation (no one can say 'Hey, if you had a mass spectrometer and three months you can do this check' - it clearly isn't feasible for that question but is for this one. This question is marked as a duplicate of that other one.

The background of this question is that the crew have gone out intending to find new worlds, they collect data on each world they pass and, if they seem more viable for life they land and assess the planet. A food source is one of the things they check for.

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    $\begingroup$ I think you should better define their capabilities and knowledge, especially from the analytical chemistry point of view. $\endgroup$ – L.Dutch - Reinstate Monica Jul 28 at 10:07
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    $\begingroup$ Definitely related: Would humans be able to derive nutrition from foodstuffs found on alien planets? Full disclosure: My own question. $\endgroup$ – a CVn Jul 28 at 10:58
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    $\begingroup$ @aCVn Definitely is related - I hadn't thought about chirality, that something could appear identical but provide no nutritional value. Filling you up but starving you all the same could be a form of poison. $\endgroup$ – Lio Elbammalf Jul 28 at 11:30
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    $\begingroup$ @john sure, they've got a ship which can produce food, they can subsist off that until they've found alternatives. $\endgroup$ – Lio Elbammalf Jul 28 at 19:13
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    $\begingroup$ This is what Red Shirts are for. $\endgroup$ – manassehkatz-Reinstate Monica Jul 29 at 4:53

A multi-pronged strategy.

  • First, simple chemical tests would be performed for heavy metals and strong acids/alkalis and to give a general profile of the plant or animal's chemical composition. Gas chromatography should throw-up a number of interesting results and help identify known poisons. This, whilst being careful to identify any specific part of the organism which could be toxic - think of the puffer fish, a delicacy, but deadly if not prepared correctly. - This would filter out some obvious toxic candidates. Look out for chirality too, the "handedness" of molecules makes a big difference to compatibility.

  • Mice would be fed a diet with the addition of these various food stuffs in a clinical trial like way with a control group fed a known safe diet. Blood workups would be taken, testing for unusual changes including signs of stress and hormone levels. They would be observed for behavioral and digestive changes and any signs of poisoning or infection by parasites. Pregnancies would be allowed to go to term and the newborns examined for any mutation or abnormality (preferably their genomes would be examined for mutations outside the normal statistical range). Eventually culling them and dissection of some would reveal any signs of cancerous growths or other unwanted effects. - Another stage further towards the goal.

  • Microbiological screening would be done with a variety of human tissue cell cultures to establish if any toxins present can damage them. Some candidates would be; liver, kidney, smooth and striated muscle tissue, nerve tissue, pancreas and skin.

  • Tentatively, human volunteers would gradually introduce some (small at first) samples into their diet, being closely monitored for effects (it might be as well to have a control group here too and make it double blind - ie neither the doctors nor the test-subjects know who's getting the "real thing" till after a the test has gone on for a while). If satisfactory, the amounts in the diets could be increased in stages.

This whole battery of tests would be performed on a variety of samples, soon it should become apparent the sort of toxins present or likely to turn up as a profile of the ecosystem's chemistry becomes clearer. Eventually, assuming any compatible substances are found to be both nutritious and safe a diet could be formulated suitable to sustain life. At that point, flavor, mouth-feel, and smell gain importance.

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    $\begingroup$ This is how we do it on earth; same as we'd do it in space. $\endgroup$ – Mazura Jul 28 at 19:10
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    $\begingroup$ We should also check the nutritious value of the edible food, so as to make sure you don't end up eating negative calorie food. Something that takes a 1000 calories to digest, and only provide 800 calories, sure way to lose weight and end up dead. Same way make checks for protein, vitamins, etc. $\endgroup$ – V.Aggarwal Jul 29 at 10:41

Apply the Universal Edibility Test (it is universal!).


  1. Separate the plant into its various parts—roots, stems, leaves, buds, and flowers. Focus on only one piece of the plant at a time.
  2. Smell it. A strong, unpleasant odor is a bad sign.
  3. Test for contact poisoning by placing a piece of the plant on your inner elbow or wrist for a few minutes. If your skin burns, itches, feels numb, or breaks out in a rash, don’t eat the plant.
  4. If the plant passes the skin test, prepare a small portion the way you plan to eat it (boiling is always a good bet).
  5. Before taking a bite, touch the plant to your lips to test for burning or itching. If there’s no reaction after 15 minutes, take a small bite, chew it, and hold it in your mouth for 15 minutes. If the plant tastes very bitter or soapy, spit it out.
  6. If there’s no reaction in your mouth, swallow the bite and wait several hours. If there’s no ill effect, you can assume this part of the plant is edible. Repeat the test for other parts of the plant; some plants have both edible and inedible parts.
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    $\begingroup$ I appreciate some of these things could work but other, smell for example, only work because we evolved to find those odours and tastes unpleasant - a plant evolving on a different planet would have no reason to have the same make up as our own. $\endgroup$ – Lio Elbammalf Jul 28 at 11:32
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    $\begingroup$ @LioElbammalf Very true, but there are poisonous Terran plants that don't have a bad odour either (remember than cyanide smells quite nice). The test is designed to rely on multiple physical responses. Of course, their is nothing to guarantee that following this advice on the planet X won't result in an alien bursting out of your stomach a week later so neither I nor my heirs will accept legal responsibility for any ill effects resulting from this answer. $\endgroup$ – DrMcCleod Jul 28 at 12:43
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    $\begingroup$ In this case "universal" means everywhere on Earth. It deliberately excludes the more obviously stupid choices. Mushrooms would pass all those tests, but if you eat the wrong kind, a week or two later your internal organs will start shutting down and you'll die. Similarly, eating very small amounts of chocolate will have no obvious effect on dogs, but frequent consumption can shorten a dog's life by years. There's no way to know that any specific alien plant isn't the equivalent of a mushroom to a human or chocolate to a dog. $\endgroup$ – Ray Butterworth Jul 28 at 13:23
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    $\begingroup$ Testing on yourself is for survival situations. $\endgroup$ – Mazura Jul 28 at 19:10
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    $\begingroup$ Death cap would pass all of that. No burning, no itching, no strong unpleasant smell, tastes OK, the first symptoms appear only after a day or two, at which point the only "cure" for you would be a liver transplant. And, according to a mycology lecture I once watched on youtube, many mushrooms didn't, actually, co-evolve with animals to kill them - mushrooms are ancient, they became the way they are long before the animals became the way they are. They simply "don't care", so to speak. $\endgroup$ – Headcrab Jul 29 at 5:41

Don't bother. There is no reasonable chance that any non-earth life will be "edible". The human digestive system can only derive nutrition from a tiny fraction of the lifeforms on Earth. That's true of both biomass and number of species. And for the lifeforms we can eat, we can only eat a fraction of them. We can't eat wood, chitin, bone, hair etc. We will have to bring all our food with us, and have our bacteria and plants convert base materials into food for us.


Bring a monkey and eat what it eats.”

I have no supporting evidence at this time but an old saying in my area is “bring a monkey and eat what it eats” It may come from the fact that monkey is so close to human such that if something is safe for monkey, it is safe for human. Birds, on the other hand, can eat stuff that is not suitable for human.

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    $\begingroup$ Nice first post! But. don't monkies eat their own poop? I guess if the monkey won't eat anything, you can always eat the monkey. So no matter what happens your covered. $\endgroup$ – EDL Jul 28 at 18:52
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    $\begingroup$ This answer is best in combination with the story premise that intelligent design has actually turned out to be true. Then you can state that we've already discovered general rules of thumb (such as, "If you can breathe the air, you can eat the grain"). $\endgroup$ – EvilSnack Jul 29 at 2:58
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    $\begingroup$ This is a good way to kill off a bunch of monkeys and learn what not to eat in the process. $\endgroup$ – Mad Physicist Jul 29 at 12:43

The best method is a tiered combination of methods. Under the assumption the colonists are trying to find a suitable food source before their own stores run out a tiered approach is best.

  1. Common sense, don't eat scavengers or parasites (both mobile and not), be wary of anything immobile, don't eat anything that is dramatically colored compared to other wildlife. These are all things that make parasites and toxins more likely.

  2. Chemical analysis to make sure no obvious toxins are present, common elements on one planet might not be on others, arsenic might be widespread. The local wildlife will have evolved with it and thus it will be harmless to them but toxic to humans. You will also want to do this for nutritional information, eating all the local wildlife you want will not help if none of the local wildlife has any vitamin B, or only has lefthanded nucleic acids. You also need to make sure they use molecules of the same handedness, if not your colonist will be better off commiting suicide.

  3. Animal testing, rats or dogs for cost, chimps if cost is not an issue. Of course if you have lots of earth animals you should be eating those instead. If you don't have earth livestock, Start with human gut cultures and cloned tissue instead, otherwise these will be the next step. Consider starting with products fermented by earth bacteria, alien product/earth bacteria cheese is one of the few things with a decent chance to be edible.

  4. Cook everything, many parasites and toxins will be destroyed by cooking. It also means they need to eat less of the alien food (cooked food has much higher nutrient availability) and thus reduces chances of an adverse occurrence.

  5. The universal edibility test, Timing is important in this test, and it checks for things like allergic reaction and acute effects earlier tests will miss. You will almost certainly lose people at this stage. Allergic reaction is going to be a big worry since there is a large risk of novel molecules. This is something that can only be tested directly on humans, even tissue exposure test will not catch many allergies, so including this step will be important. Each human will have to do each test for each food but you don't want multiple people testing the same food at the same time. preferably you want days separating them. There will be quite a bit of conflict here as they decide who the most disposable crewmate is. Note you are going to want to add another few steps to this, first prior to injection a pin prick test will be useful. during ingestion testing you will want to start with minute quantities and work your way up to substantial amounts.

All combined you are looking at months before anyone actually eats anything, and depending on the number of colonists years before everyone is eating it.

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    $\begingroup$ Parasites and toxins in an alien environment might be delicacies in ours... $\endgroup$ – Mad Physicist Jul 29 at 12:43
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    $\begingroup$ @MadPhysicist, they might, but if they are digestibly compatible chances are many of them will be dangerous. That is the kind of experimentation you save for long after the colony is self sufficient. $\endgroup$ – John Jul 29 at 14:18

Why would space travelers "go native" and start eating food that grows on an alien planet?

If their spaceship can keep them alive on the journey to an alien planet presumably it can keep them alive while exploring the alien planet and on the journey back to where they came from.

Presumably the spaceship would have food synthesizers to convert stored materials and waste materials into food and water and enough energy to run the food synthesizers countless times.

Presumable the alien solar system would have many small bodies, comets, ring particles, asteroids, and meteoroids, and many of those small bodies would contain many of the elements and compounds which could be used as raw materials by the ship's food synthesizers if raw materials storage units on the ship leaked and lost a lot of material.

So space explorers would probably not have much need to test alien life to see if it is nutritious and non poisonous.

Maybe people intending to colonize the planet would want to eventually know what native foods are safe to eat.

There are two possibilities.

One, they are headed for a specific planet which they know they can colonize. Presumably they would have extensive reports from explorers about which native plants are edible before choosing that planet.

Two, they are on an expedition looking for a suitable planet to colonize, either for themselves to colonize or else to report as safe for colonization by other persons. Then they would have to do a lot of tests on the native biosphere.

First they would analyse a lot of sample of the atmosphere and water from all regions of the planet and all the various types of habitats, looking for concentrations of harmful chemicals.

Then they would have to inventory all the plant life on the planet, classifying and cataloging thousands and probably millions of species. And a specimen of each species of plants would have to be chemically analysed both for nutritious chemicals and for poisonous chemicals. Confounded by beige's answer suggests a series of various types of tests.

If a strong lack of nutritious chemicals and/or strong presence of poisonous chemicals is detected early in this investigation, the planet will probably not be suitable for colonization, so some planets can be eliminated from consideration. And if the investigation continues long enough for the planet to be cleared for colonization, there will already be a long list of which plants and plant parts are edible, and which are not.

But of course colonists might not want to "go native" and eat plants that grow on the planet. They might simply take gaseous, liquid, and solid matter from the planet and put it into machines that separate it into separate elements. Elements useful for making machines and other items will be sent to 3D printers that can make what they need and desire, while elements useful for making food will be sent to food synthesizers. All of the colony's waste materials will be recycled into the matter supply for the colony.

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    $\begingroup$ This does not invalidate the question the "explorers" will need to have a method to test the food as well. $\endgroup$ – John Jul 28 at 18:39

Assuming a realistic alien world, the simple option is assume everything is non-nutritious or poisonous. You'll probably be able to get some micro-nutrients such as calcium or iron from native plant life, and if you're very lucky, you'll find something that produces ethanol. Most likely, though, is that everything has the same nutritional value as a rock.


I'm afraid you're already dead.

If the world is truly 'alien', it would have evolved a completely different ecosystem, in a completely different way. The odds of the billions upon billions of mutations and evolutionary changing events being identical to Earth's (to our time period too) is virtually non-existent.

Even on Earth a small difference in evolutionary biology for, say, bacteria is fatal - imagine a 'bacteria-like' microbe that our immune systems are completely unprepared for on an alien world. We would have no chance to survive.

In fact why stop there? Viruses that our immune systems have gradually grown resistance to are essentially large molecules - having a 'soup' of foreign viruses would completely overwhelm us within seconds, invading through our mouth, and even our skin.

Our bodies have extraordinarily low tolerance - infections and immune responses are only built for Earth organisms with structures and chemicals that closely align with what is already evolved. If it varies a little too much from the established norms that our immune systems have evolved to combat than it is quickly fatal (hence, current-day large research into anti-biotics which our immune systems cannot handle)

Even if we live in an isolated habitat, any lifeforms we bring from the outside would be saturated in a foreign ecological systems equivalent of bacteria-sized microbes and viruses (or their alien equivalent, which is likely if the foreign ecosystem has grown larger organisms) which would prove quickly fatal and contaminate your internal environment.

Very unromantic I know, but unfortunately true.

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    $\begingroup$ Alien viruses should be harmless. Viruses are very specialized machines that commandeer host cells to produce more viruses. They won't be able to hack DNA fundamentally different than what they evolved against - if that's DNA at all. Bacteria is much more dangerous and could wipe us out, but they're as unadapted to us as we're unadapted to them, and we will definitely use cheap tricks like extended boiling, which may well be unprecedented in the planet outside of volcanic areas and forest fires. $\endgroup$ – Emilio M Bumachar Jul 29 at 11:38
  • $\begingroup$ Our bodies however haver relatively good passive defense, alien bacteria is unlikely to find us as a compatible substrate, especially given the blanket of earth bacteria we carry around with us. $\endgroup$ – John Jul 29 at 14:24
  • $\begingroup$ I do not think our bodies have good 'passive defense' in an alien environment. The point is that our bodies do have good defense, but only against what it has evolved to defend, that of a similar ecosystem. It has no defense against an alien environment at all. $\endgroup$ – flox Jul 29 at 15:06
  • $\begingroup$ Our immune systems are built for a whole lot of things that aren't Earth-derived life. Sure, our T-cells might not be able to kill off alien bacteria, but that's hardly the only response available. Part of the challenge of designing medical implants is finding materials that our immune system won't attack. $\endgroup$ – Mark Jul 30 at 19:57

No extraterrestrial life form will be edible. To be edible the food should contain nucleic acids or proteins, also fatty acids and vitamins that are specific to erthy life and won't appear in extraterrestrial organisms.


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