Headcanon W-#@-?/!-------[ERROR] : Eating Alien Food
People from different species are driven to share together what matters to them : food is one of these.
But can you even eat food that isn't from your homeworld ?
[The first part of this post is largely based on Biblaridion's video on the same topic.]
The easy answer is, yes. After all, everyone* is able to eat varren skewers, varren steaks and varren cloaca margarine, even though they may have not personally evolved on Tuchanka. Everyone* is also able to drink Tupari ! made with as much as 10% of delicious, delicious tupo berries. There is a thriving meat printing industry even though you can't get them to make anything that tastes like krogan or BBQ asari.
What's that pesky asterisk going on about ?
Oh, right.
The science
Not everyone can eat and drink varren pap or murderous sports drinks ; there are various dietary restrictions :
there's the familiar levo/dextro divide : everyone but turians and quarians have evolved in a biosphere where you can only consume, digest and metabolize safely levo (left-handed) amino acids. We'll get back to that in a few.
volus (and everything they eat) do not use water as a solvent : they use ammonia. It's likely ordering what your volus date is eating will be your very last meal.
it's amazing how much radioactive stuff a krogan can stomach.
Thessian food is laced with eezo, a carcinogenic material, to the point that visitors to Thessia are strongly encouraged to stick to the visitor menu if they, uh, don't wanna die. Conversely, not eating food laced with eezo will ultimately prove detrimental to asari, as their physiology relies on eezo to some extent.
But the rest is safe, right ? I can eat that blue fruit I picked on an alien world that looks like a bubonic clitoris ?
Oh, no. Another list.
some species do not eat the same things. Turians and batarians are obviously geared for carnivory, whereas elcor have evolved for herbivory. They cannot digest the same food stuffs the same way you can't digest wood or grass. These species probably lack the teeth to even properly deal with food they haven't evolved to eat.
and there's the question of taste buds : if your ancestor species got their daily food intake from fruit or nectar, you're likely to be disproportionately shaped to identify and appreciate (CRAVE) sugar. Conversely, more carnivorous ancestors will result in being more sensitive to certain chemicals present in meat. So even if you may be able to eat the same food, you are unlikely to taste the same thing that your alien buddy, and you are therefore very likely not to enjoy the experience. See also what happens in Andromeda : to an asari (Peebee), angaran food smells great but tastes bad, whereas for an angara (Jaal), Milky Way food (presumably human food) tastes bland (in part at least because angara cannot register capsaicin, i.e. the active component in chili peppers), but methyl anthranilate (commonly used as a flavoring agent in candy, Kool-Aid, grape-tasting soft drinks or chewing gum, and naturally occurring in most grapes, but also in lemons, mandarins, oranges, strawberries and apples) causes a painful burning sensation.
let's not even get into the particulars of different cultures and what each considers "good food".
But… but it's all the same chemicals, right ? Even if you don't like it, you can still eat it, right ?
Right ?
What do I, a human, need to imbibe, ingest, and otherwise intake ? In other words, what does my saggy, saggy human body (and yours) need to function ?
water ; easy peasy lemon squeezie, the stuff is everywhere in the universe and mostly everyone drinks the stuff (sorry volus)
proteins, your friends the amino acids — nine of which you need to get from your food (valine, phenylalanine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine), and many others you can synthesize yourself, you lazy fuck. You can learn more about proteins here.
lipids, your better friends the fatty acids, especially linoleic acid and α-linolenic acid.
carbohydrates, including everybody's best friend, glucose.
vitamins : A, B1, B2, B3, B5, B6, B7, B9, B12, C, D, E, and K.
minerals : potassium, chlorine, sodium, calcium, phosphorus, magnesium, zinc, iron, manganese, copper, iodine, selenium, molybdenum, cobalt — note that most of these quickly become toxic if you ingest too much of them
and don't forget your basic building blocks : carbon, oxygen, nitrogen, hydrogen — those are easily derived. And they're, like. Super abundant.
If you're a carbon-based, water-chugging lifeform, you can only eat stuff that's also carbon-based and water-chugging. So, again, you can't eat the beasties on Patavig or a volus, (presumably) carbon-based but (definitely) ammonia-chugging ; and you can't eat the (presumably) water-chugging but (definitely) silicon-based beasties on Caleston : the ammonia from Patavig would kill you, and the silicon from Caleston means you have no proteins, no lipids, no carbohydrates, nothing edible.
But don't go and start licking a krogan just yet !
There's still a problem.
What makes you think a carbon-based lifeform would have evolved to rely on the same carbon-based molecules you depend on ?
Chirality is the best-known example, though most people assume it's simpler than it really is : humans feed on proteins (amino acids) that are (almost exclusively) left-handed (levo), and on sugars that are (almost exclusively) right-handed (dextro). As a reminder, a left-handed molecule and a right-handed molecule are the exact same molecule, just mirrored.
The question is : is there a reason evolution would favor one kind of chirality over another, or is this purely random ?
Answer : we just don't know (this will be a pattern), because when we study the way life develops, we only have a sample of… one (1).
That being said… I don't know about anyone who's come up with a viable theoretical basis to justify why life would be restricted to a specific version of a molecule — and moreover, within the fictional universe, the question is moot anyway : life based on the "wrong" mirrored molecules clearly does exist (turians, quarians), meaning that within the fictional universe there's nothing "forcing" life to stick to forms easily digestible and metabolized by humans. :'(
But it's not just chirality, really : not only alien lifeforms might use mirrored versions of the carbon-based molecules we depend on, but they could use entirely different carbon-based molecules — just like they don't necessarily use the DNA molecule as the carrier of genetic information. From what little we know and understand about life in the universe based on our sample of one (1), there's nothing ""inevitable"" about the building blocks that make… us.
Moreover (as Biblaridion points out), even if alien food does contain the molecules we need, they are usually "locked up" in larger molecules that need to be broken down by enzymes ; each enzyme is able to break up a specific kind of molecule into the molecules we actually need (hence : lactose intolerance for people who lack the enzyme lactase). Quoth Biblaridion : "So, in order for humans to gain any nutrition from eating an alien lifeform, they would need to have the enzymes necessary to break down the larger and more complex molecules in the alien food into simpler nutrients. … As a result of [an enzyme's specificity to a unique compound], a given species will only be able to metabolize molecules that it has the corresponding enzymes to cope with, which will be inherently limited to those molecules that occur in the foods that it has specifically evolved to be able to digest."
What would be the consequences of eating alien food that contains at least some molecules you have never evolved to process ?
nothing. Well, nothing immediately. If you keep doing it and your body doesn't get the nutrients and minerals it needs, you'll get malnutrition and then you'll die.
the typical symptoms of food poisoning, for humans : vomiting and diarrhea, especially diarrhea (in humans, a great amount of unabsorbed sugars and products raises the colon's osmotic pressure, which increases the flow of water into the bowels, which causes diarrhea). If untreated, dehydration, possibly death. Think lactose intolerance.
anaphylactic shock, if you've got allergies. There seems to be a fair possibility, given how part of the standard sex talk when you start hooking up with someone with dextro biochemistry is to not, hm, ingest.
the lethal kind of food poisoning : food that's downright toxic and hazardous. Biblaridion gives the IRL example of the molecule thalidomide, which has starkly different effects on the human body depending on its chirality : left-handed thalidomide is commonly sold as a drug to treat various cancers, skin diseases, or different conditions associated with HIV, and has a mild sedative effect, whereas right-handed thalidomide is teratogenic, i.e. it causes birth defects in an embryo. What is life-giving and necessary to others might prove a literal poison to you, and it's basically random chance for every molecule.
The exact reaction to a specific kind of molecule or food product will be entirely dependent on individual genetic quirks and one's species' biochemistry ; in other words, the alien food that is deadly to you might mildly indispose a salarian and do nothing to a drell. But the odds that different lifeforms would evolve to consume the very same molecules you rely on are… very, very, very, very small.
(And even if you can digest it, it would probably taste different to your alien date and to you.)
Okay, then ; how do we square this inability to digest food that didn't evolve from your homeworld with what we see in game : people partaking of and sharing different foods regardless of origin ?
The canon
It's important to stress that within the games, the only hard limit appears to start with either the presence of exotic toxic compounds (e.g. eezo for Thessian food, hence the prevalence of "visitor menus") or the levo vs. dextro chirality issue : throughout the games, it is repeatedly stressed that turians cannot "live off the land" on most planets, which impacts their logistics in military operations, and we see various mentions and instances of the presence and danger posed by food with the wrong chirality, as well as accommodations to prevent ingestion (e.g. the Mordin sex talk if you romance Garrus, Matriarch Aethyta specifying that dextro finger food is in red bowls — does that mean the levo food is in blue bowls ?), which overall show a socio-political effort to make people aware of the dangers of chirality-based food poisoning we see no equivalent of for more specific types of food, beside the batarian food burgat, which has an extensive disclaimer ("Burgat is composed of levo proteins and is not suitable for consumption by turians or quarians. The Burgat Export Company takes no liability for allergic reactions or intestinal parasites in non-batarians.").
EDIT : Note that beside "dextro" and "levo", there are additional, seemingly more formal adjectives (for spices at least) in ME2, at the Zakera Café : amino-dextrous and amino-sinister.
Nonetheless, there is this unchallenged assumption of broadly similar biochemistries in the levo group : Khar'shan parasites can be an issue to you ; most people can seemingly drink each other's booze as long as it does not contain methanol, even though anything that isn't pure ethanol would contain a variety of organic compounds that may or may not have a detrimental effect ; and some drugs, like Hallex, seemingly affect multiple species in identical fashion. This shouldn't be possible.
The unfortunate reality, as ever, is that the Mass Effect writers didn't think about it because none of the major scifi franchises thought about it ; but in fact, because it considers chirality, Mass Effect does a better job than Babylon 5, Farscape, Star Wars, Star Trek, or any otherwise Star-named franchise. Nonetheless, there's still context to be made out, especially answers to the following questions :
how is food produced in the Mass Effect universe ? i.e. space agriculture
who has access to what food where ? i.e. space food economics
At the beginning of Mass Effect : Andromeda : Initiation, Cora realizes midway through a meal that what tasted like Earth shrimp probably is in fact an insect analogue from Horizon, which comes with an unfortunate mildly laxative side effect, which is in keeping with what we've established. This suggests that :
for humans at least, you really or rarely can't beat eating food from your native biosphere, which absolutely would drive up the cost of such food products because there's only so much of it you can produce…
and therefore, in at least some cases, there is an economic incentive to replace an ingredient from your native biosphere with an alien alternative that can't be explained just with transportation costs (Cora eats her non-shrimp aboard Tamayo Point in the Sol system itself, infinitely closer to Earth than to Horizon : transporting shrimp to Tamayo Point would be far less expensive than transporting Horizonian bugs to the same).
But there are happy accidents sometimes : a food product that does not come from your biosphere but which nonetheless fits your biochemistry (seemingly) perfectly. Such is the case of the high-nutrition vine known as ossilbir, which comes from an unspecified world that is not Earth (after all, ideal growth conditions include 90% average humidity) but has nonetheless become an Alliance military staple, and is presumably eaten by many people beside the Alliance ("most levo-amino-based sapient species"), since at least 60 Citadel worlds buy or sell products made from Sathur-grown ossilbir.
Moreover, alien animals are at least partly edible for humans : after all, eating varren meat is specifically an option a starving human colony considers to "boost rations", and there is a whole galaxy-spanning food chain dedicated to selling bits of varren (Fishdog Food Factory (a division of Elkoss Combine)) while another company sells some kind of varren… byproduct (MrSorley's Cloaca Margarine). Additionally, edible arthropod-like animals shipped from Yamm to the small resort stations orbiting neighboring Tefnut are considered "luxuries" (alongside "large amounts of fresh water"). So alien food products can run the full gamut of quality and expensiveness, from cheap, diarrhoeic substitute (Horizon insects replacing shrimp) to institutional staple (ossilbir) to everyday food (varren meat and margarine) to luxuries (Yamm arthropods).
But importing alien flora and fauna onto a settled world comes with risks, as the politically-and-economically-motivated decision to grow ossilbir on the planet Sathur was met with virulent protests (and violent repression), as the protestors feared that "the new plant [would] overrun entire continents", with the textbook worst-case scenario seemingly being "the almost-uninhabitable garden world of Cassilda" for "an example of what can go wrong when a non-native species is introduced to a new environment." (Interestingly, the textbook example is not Pragia (see below) but this otherwise unmentioned planet — possibly to relate to "how rapid [asari] expansion had damaged the ecologies of other planets" prior to the settlement of Sanves in 544 BCE, leading to the asari restricting settlements from Sanves onwards.) In other words, growing alien flora/fungi/whatever or breeding alien animals on a settled world is (or at least can be) a controversial decision. The risk caused by invasive species is a very real danger even outside of agriculture : varren infestations (not to mention thresher maws) that wreak havoc on a native ecology have been apparently fairly common.
Pragia is a much closer example of bad interstellar agricultural practices : Batarian Hegemony agribusinesses selected it to be their breadbasket in the late 20th century CE, and "non-native, industrially mutated plants" were introduced ; though they flourished in Pragia's "fertile volcanic soil", the unexpected synergy of the non-native species with a local species had dramatic, devastating side effects — in this case, the "industrially mutated plant species" synergized with Pragia's "natural geothermic conditions and chemotrophic microbes", resulting in "choking hypergrowth" that can overgrow "colonies in days instead of years" as well as "mutant strains of poisonous and even carnivorous plants". The planet was abandoned, and as Pragia's small animal population is unable to check its plant growth, total soil exhaustion is expected to take place by the late 26th century — i.e. no plants will be able to grow, the entire biosphere will collapse, and Pragia will be devoid of anything bigger than a microbe.
The encounter between species native from different biospheres can have less dramatic unexpected consequences : in Sathur's case, a native mold developed on the ossilbir grown there which, while non-toxic, proved to have powerful hallucinogenic effects — and immediately became a new drug known as creeper, fetching record prices at 9,000 credits per gram on the black market within a week of its being reported as a health issue, leading to an immigration and smuggling crisis within another week.
This sheds some considerable light on one of the best examples we have of agricultural practices : Horizon.
A temperate world that has hit the "sweet spot" for carbon-based life, Horizon has a nitrogen-oxygen atmosphere maintained by abundant indigenous photosynthetic plants and bacteria. While the native plants are not very palatable to humans, the soil conditions are such that a handful of introduced Earth species have flourished, and the colonists must take strict care to prevent ecological disasters. Genetically-engineered "terminator seeds" that grow nutritious but sterile crops to minimize outbreaks are the rule rather than the exception. Animals on Horizon appear to be exploding in diversity, similar to Earth's Cambrian period. Large flying insect analogs take advantage of the thicker-than-Earth atmosphere and low gravity to grow enormous. Microbial life has proven relatively benign; a series of vaccinations for the most virulent strains of soil-borne diseases is all that is required for a visit.
The important bits are as follows :
"the colonists must take strict care to prevent ecological disasters" : it is all the more interesting because Horizon is an independent colony specifically founded, per the planet's Codex entry, "as a refuge from the increasing restrictions of Citadel-governed society". This establishes that at least some independent settlers in the Attican Traverse or the Terminus Systems are mindful enough of ecological disasters that they take steps to set up sustainable living and agriculture without the regulations and looming authority of an overarching law system. Which makes sense with what we've just seen with Sathur, but it's impressive : it suggests at least a widespread "common sense".
we already know that the Horizonians kill and export at least some of the local enormous flying insect analogues, and that they give you the runs.
if the native Horizon plants aren't very "palatable" to humans, then taste seems to be the only significant (but seemingly insurmountable) obstacle to foraging and local plant domestication, not incompatible biochemistry. This suggests that colonists expect, to some extent, to rely on local wild species for subsistence.
…and if that is the case, then settlers take it as a given that they can usually safely process the alien plants they might eat. Which makes sense, as this makes them less reliant on imports, which makes sense both economically and security-wise.
This also means there's someone (or some people) whose job is to analyze local autotrophs, determine whether they're poisonous, and, once they're confident the edibles are safe to eat, take a small bite for a man, but a big chomp for all of humanity… then try various cooking techniques to make them better tasting.
The safe introduction and culture of non-native plants (in this case, "a handful of introduced Earth species") is possible on an alien world with terminator crops, i.e. plants genetically engineered to be sterile, as otherwise an unaltered species might reproduce on its own and become an invasive species.
Presumably, the plants the Horizonian settlers import do not rely on pollination (i.e. animal-assisted reproduction, with bees for instance), as otherwise there'd be no need to alter them, they could not reproduce on their own anyway. That, or the risk of a stray Earth pollinator reaching imported flowering plants is too great.
It's worth pointing out that terminator crops make settlers extremely dependent on the genetic engineering firms and the prices and conditions they set, in a way that no farmer on Earth is at present, in spite of the already extremely precarious conditions of their professions. One of the key aspects of the opposition to GMOs in agriculture IRL is that any company, like Bayer-Monsanto, which sells you terminator seeds year after year after year, basically owns you. We might expect this would create an incentive for settlers to get unmodified crops (or get pollinators and flowering plants) to get out of this economic dependency, thereby introducing invasive species and devastating alien ecosystems ; the fact the Horizonians don't is, in that regard, all the more remarkable (and praiseworthy).
however, there are two conditions which might stop people from growing outworld plants in alien soil : the first is general soil conditions, which in this case are optimal and allow the Earth plants to flourish, but which are certainly hostile on other planets (as is the case on Triginta Petra) ; and the other is local soil-borne diseases, and here once more the local microbial life is (surprisingly ?) benign, and in this case vaccinations are all that's needed if you plan to sample the local cuisine on your visit. It's somewhat amazing that vaccinations have already been developed to address this very local issue in such a short amount of time since the colony was founded. The phrasing in Horizon's description suggests that, in some cases, there are far more and fare more virulent soil-borne diseases, and that steps more drastic than vaccination are required in order to eat local food safely.
finally, the fact the local settlers immediately start growing their crops directly in Horizon's soil once they establish it's safe instead of relying on the safer, more controlled environment of a hydroponics facility seemingly suggests that growing crops directly in an alien planet's soil is preferable to hydroponics if it is at all possible, presumably because of the costs related to set-up and maintenance costs of hydroponics, with a lot of infrastructure.
Over in Andromeda, we have a few examples of settlement technology specifically related to agriculture :
ISRU processors : they extract hydrogen and oxygen from the soil for use as vehicle fuel or as an emergency water supply ;
ionic water filters : if necessary, they modify alkaline levels in ground water and make it potable ;
soil converters : they convert sand into arable soil, obviously for soilborne agriculture as opposed to hydroponics (suggesting once more that the former is preferable to the latter).
Hydroponics (i.e. growing crops without soil) is something which happens off to the side in the OT : when you get Javik on Eden Prime in ME3 you can walk through prefabs where it's clear that's what's going on ; "hydroponic food", seemingly grown locally in orbital space stations, is mentioned in passing ; and it's explicitly what the quarians are up to aboard the Migrant Fleet's Liveships. There are no mentions I can think of something we'd expect : agricultural space stations, partially or fully dedicated to hydroponics.
(The quarians also engage in something that definitely isn't hydroponics : beside the "plants and fungi … specially developed to thrive in hydroponic conditions", they also grow some of their "genetically modified staple crops" in "highly enriched soil". The lack of soil is the defining feature of hydroponics.)
Hydroponics gets a spotlight in Andromeda with its very own Codex entry, which retroactively sheds light on how space hydroponics probably happens back in the Milky Way :
water ice is harvested somewhere in the universe
it undergoes "reverse osmosis" to remove heavy metals
the water is then "divided into reservoirs for each plant variety"
"a macronutrient mix is added" to each, presumably tailored for the respective needs of each plant variety
"VI systems constantly monitor the pH, temperature and dissolved solids count of these reservoirs"
the plants are grown under "artificial light" which presumably requires a lot of energy. On Earth, hydroponic plants are drawn under telltale violet light to give them only the wavelengths of light they'll eat — so presumably, different plants from different planets grow under different lights.
aboard closed environments like the Nexus, the plants are chosen "by crop variety and oxygen yield", as they "improve overall air quality". Moreover, if hydroponics is done in common areas, the plants also have a psychological effect as they improve morale.
It is likely the "gro-labs" mentioned offhandedly by Juliana Baynham on Feros are hydroponics facilities, as Baynham mentions insecticide (another thing that people growing crops still depend on, despite the obvious prevalence of GMOs throughout the galaxy). Meanwhile, an "agricenter" may suggest a closed building on an inhabitable world where soilborne agriculture happens ("soil tests"). Finally, an "agri-habitat" appears to be a sealed autonomous building on a hostile, uninhabitable world where food is grown ; what type of agriculture is going on there is anyone's guess, but the mention of "greenhouses" and especially "compost" suggests that, on Logasiri at least, soilborne agriculture is taking place.
Note that so far we've largely been talking about crops, i.e. autotrophs (i.e. organisms able to synthesize their food themselves by drawing on an outside energy source, such as light). What about heterotrophs, i.e. organisms who need to eat other organisms to survive, i.e. livestock and game animals ?
It's worth pointing out breeding animals in space ! would be even harder than growing crops, because you also need to breed their food (which is why, historically, we've never domesticated carnivores : you need to raise animals they will eat alongside them and to get those animals their own food ; in that regard, the domestication of varren seems like an anomaly at first, until we remember the varren are canonically omnivorous), and yet we humans need* to eat animals or animal byproducts to get proteins.
* : Well, "need" : technically, humans can get by on a vegan diet as long as they can get B12 supplements too ; I'd argue that the constraints of space travel and space agriculture would incentivize space veganism and a major B12 industry (with the caveat that animal protein is easier to assimilate than vegetal protein, which may have been important, historically speaking, when humans didn't have access to artificial gravity), if there weren't additional elements to consider. Sorry Big B12 !
Ideal space livestock would be comprised of species which a) are easy to feed and care for, b) don't take up too much space, and c) have a fast growth and reproductive cycle (because if it takes years for them to reproduce, you're waiting for years until you can eat them since you need different individuals to make up for the one you killed)**, which is why many scifi authors have independently settled on insect farming… which we see no evidence of in Mass Effect†. So what do we have instead ?
** : Worth pointing out that the ideal space livestock is also the ideal invasive species, which may be why we see no evidence of insect farming. † : What we do get is this : the quarians don't have insect farming and are vegan precisely for the reasons I've just outlined, which completely makes sense as Rannoch has no insect life.
Instead, what we have is vat-grown meat and live livestock.
Vat-grown meat (i.e. animal bits artificially grown from cell cultures, without killing any animal) is mentioned in passing a few times, the best part being in Mass Effect: Homeworlds #1 (the James Vega issue)…
CALIFORNIA COOK ON A SMOKE BREAK #1 : I can't tell the difference. Customers can't tell, either — it tastes the same. CALIFORNIA COOK ON A SMOKE BREAK #2 : But beef grown in a tube — it just ain't right. CALIFORNIA COOK ON A SMOKE BREAK #1 : Don't let on you know. The boss doesn't like us talking about it.
…which tells us a few things !
The issue takes place in 2176, and meat-growing was a fairly recent technology by then — suggesting meat-growing was actually developed by non-humans first.
This cruelty-free meat and meat drawn off a dead animal literally taste the same.
Nonetheless, it's considered somewhat shameful among humans for restaurants to use vat-grown meat instead of, er, natural meat.
Finally, vat-grown meat is less expensive than natural meat, strongly suggesting that, despite the set-up costs, it costs less to grow bits of animal in a lab than to grow the same bit on a live animal the old-fashioned way.
(Nevertheless, referring back to the quarian example, if meat culture was easy or/and inexpensive to set up and operate, the quarians would be doing it.)
It's highly probable that this meat-making is what EZ Meat Inc. does ; they have an outlet on the Citadel, an online catalog, and can ship their products ordered remotely.
But nonetheless, there's still a market for livestock and natural meat ! Even if we assume that the Earth shrimp or Horizon insects were grown in a lab (which is unlikely at least for the Horizon insects, since they're a naturally occurring resource on Horizon and why would you grow an animal that gives you the runs instead of shrimps that don't ?), we know from the Purgatory Codex entry that some spaceships are purpose-built to transport livestock — and they're called "ark ships"‡ ; and beside that text mention, I'd be remiss not to talk about my idol, the salarian on a smoke break in a Citadel cold room… filled with fish !!!
‡ : This makes Mass Effect : Andromeda a bit funny in hindsight.
So overall, when you want a specific meat item, the hierarchy in terms of cost and availability appears to be :
natural meat cut off an Earth animal
identical meat with the same taste and no additional side effects, but grown in a tube/vat/lab
some alien substitute, sometimes with bonus diarrhea
…suggesting it can be cheaper to ship in the alien substitute from across the galaxy than to get the vat-grown version, which can presumably be grown much closer to your location ; though perhaps this is only true of some animal species (perhaps you can't grow artificial shrimps that are convincing enough to pass for the real thing ? Or perhaps shrimps are uniquely difficult to grow ? Damn you, shrimps !).
But keep in mind there are times when humans want to eat non-Earth food ! (Varren skewers ! Yamm arthropods !)
The headcanons
What do people want to eat, really ?
people need to eat. Many of them need to eat daily, sometimes more than once. Consequently, people want to eat food that's readily available and that won't constitute a life-gutting expense ; that's where food economics come into play, and by extension where you live and how poor you are.
people want to eat food that is tasty ; what is "tasty" will vary depending on species (turians don't care for sweet food, elcor are horrified by meat-eating), depending on culture (it's likely you'll default on food that's familiar to you ; if you live in a big cosmopolitan city, the range of cuisines that will be familiar to you will be much wider), and depending on personal preferences (which includes variations on personal taste, and ethical considerations prevalent in vegetarianism, veganism, etc). This means that, for humans, getting "Earth food" will be a priority.
people want to eat food that doesn't impact them negatively : this includes stuff like the various bodily intolerances (lactose, gluten, etc), but also my best friend and yours (diarrhea) and up to and including death from eating what looked tasty but is actually a deadly poison to your organism.
The more technology is needed to make and bring food to your plate (including logistics), the more expensive it will get. One of the first things settlers do when they arrive on a new planet is to try and see if any of the local food is edible for at least one species ; if it is, the odds of survival for the new colony go up significantly, and the foodstuff can be grown/husbanded with ease and shipped to other people across space (if it is economical). This is ossilbir.
In practice, the odds of food being immediately edible to at least one species are exceedingly rare ; the odds of it being edible with no side effects (like the runs) are astronomical ; and then there's the thing people always forget about : just because it's nutritious doesn't mean it can be domesticated with ease (cf. Jared Diamond).
Still, sometimes miracles happen, especially if you consider that each unique biosphere each has untold billions of species ; it just takes time a lot of time to catalogue everything. This is how some drugs, like asajura, can be found and enjoyed by people from multiple species — especially if genetic engineering firms can bring out some desirable traits without breaking Citadel laws.
If you can't eat something native to your own planet, your very next best choice is to grow some of the food that's evolved for you on your homeworld — if you're lucky, you'll be able to grow it directly in the soil, and if not, you'll have to use hydroponics. Obviously, if you're on a hostile planet, you'll have no choice but to use hydroponics in an agri-habitat. Such situations strongly incentivize the development of additional sources of "homeworld food" that are cheap : vat-grown meat, insect farms, yeast-made protein concentrate if you're really desperate…
But the reality is that your average middle-class citizen of Citadel Space is plugged in a massive galaxy-wide market with century-old industries dedicated to get you better options :
food processors process alien food into edible compounds, breaking down unique macromolecules in smaller, immediately edible nutrients
the inverse of that is food synthesizers, which "print" mock-food : food that's made of compounds that are edible for your species, but which are shaped and flavored in such a way as to look like a real piece of food. EZ Meat Inc. on the Citadel specializes in that for meat, whereas the dextro chocolates Doctor Michel can gift Garrus in ME3 are exactly that : something that looks like chocolates and is made to elicit the same reaction in turians as they do in humans, but does not contain a single milligram of the real thing.
there is also the enzyme industry : one of my favorite old-timey scifi stories (W.R. Thompson's "Touchdown, Touchdown, Rah, Rah, Rah !") features enzyme pills which are taken with every meal by humans on an alien world to break down alien proteins and carbohydrates into substances that the body can use, and neutralizing whatever doesn't fit the metabolism. This would only work if it's possible to produce useful substances at all : hence why it doesn't work on dextro food. Enzymes would be produced artificially, unless explorers on the alien world can find and use native lifeforms which can produce the required enzymes on their own (e.g. basically fermentation).
the various Citadel species have existed for so long together (well over 2500 years !) that it's become remarkably easy for the levo species to share the same basic staple foods (e.g. varren and varren byproducts).
there would be a parallel industry of supplements for whatever stuff can't be found on the world itself or in the food you import. For instance, I'd expect a newly established asari settlement would import eezo salts at great expense, then keep a very efficient closed sanitation system to recycle the salts out of their, uh, waste, if there are any. Biblaridion takes the example of Niven's Destiny's Road, where the human settlers find themselves on a planet where potassium is as toxic as arsenic to the local biosphere ; the events of the novel would not happen if the settlers were part of an interstellar trade network and could import potassium.
this means closed (and probably separate) sanitation systems would be the norm, as otherwise this would be a toxic disaster inflicted on the native environment.
finally, there'd be significant pressure to genetically engineer microbes to produce the enzymes that can break down alien molecules, then insert those microbes in the gut of livestock so that they can eat and process alien flora, e.g. cows eating alien grass ; the same microbes could join the gut biome of sapient species if they are proven to be compatible and safe. The problem would be Citadel genetic engineering laws ; while creation of designed life is broadly legal as long as it isn't sentient or sapient, it can be difficult to produce and test such useful organisms in ways that satisfy the ethical demands of Citadel regulation — which is precisely why there is a thriving genetic engineering industry for such purposes in the Terminus Systems, especially on Chalkhos ; Citadel space can condemn particularly horrific scandals and reap the benefits of particularly successful programs Citadel businesses fund discreetly.
humans, being so new on the galactic scene, have very few of these adaptations and cannot consume as much of the staple alien foods as the other levo species can, hence why they will default on homeworld foods more often than non-humans on average. Earth food, on the other hand, has benefited from the lustre of novelty in the years following the First Contact War : there has been a fad for each Earth food becoming edible for one of the Citadel species for the last thirty years.
The economics of space agriculture is something that might be worth another slew of headcanons, but basically, there are enough agri-stations in orbit and agri-habitats on hostile planets and agri-centers with gro-labs on hospitable worlds that food prices aren't excessively high and some autonomy is possible — but at the same time, planets with optimal conditions for agriculture become economic powerhouses, able to specialize in food production and import everything else. As these so-called agri-worlds are exceedingly rare, they are precious and strategically vital ; it explains to some extent the continued importance homeworlds play at the center of their respective interstellar policy, irrespective of cultural valuation, as no world is better suited to grow the food you need than the world that food is from.
In Alliance space, Eden Prime and, to a lesser extent, Benning are the best known examples of that tendency, but the quintessential example might be Asteria : the development of its agricultural colonies in the 21st century (alongside the pacified geopolitical situation of the Traverse at the time) created a virtuous feedback loop with its next-door neighbor, Caleston — Caleston could import food much more cheaply because of sheer proximity, allowing companies to invest only in eezo extraction and the facilities that support it, while Asteria enjoyed the windfall of investments to satisfy an ever-growing demand. Asteria fed Caleston's development, which fed in turn Asteria's.
(Now, if someone were to do to Asteria what the geth did to Eden Prime, oh boy…)
