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For example, beans and rice cooperate to make a "complete" protein, providing all of the amino acids the body can't synthesize on its own -- in fact, most traditional dishes that combine legumes and rice are "complete". In this same way, are there three crops that are symbiotic in their nutrition? If a civilization could plant only three crops, which would be best to sustain nutrition and thus life long-term? Cheers!

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    $\begingroup$ Best? What do you mean by best? The are many permutations of 3 crops that together have all the nutrition a person needs so you'll have to specify what you mean by "best" so that we can narrow down our answers. $\endgroup$ – AngelPray Dec 9 '17 at 16:28
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    $\begingroup$ your big issue is different crops grow in different conditions, a good crop for the for temperate floodplains, will not be the same as those good fro jungle soil, or those good for dry near deserts.So you need to tell us what kind of landscape we are dealing with. $\endgroup$ – John Dec 9 '17 at 16:49
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    $\begingroup$ Some grain (e.g., rice), your beans, and hops. You'd better have the hops in order to sustain life long-term. $\endgroup$ – davidbak Dec 9 '17 at 23:08
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    $\begingroup$ Nutrition has to do with more than just amino acids and proteins. Minerals and vitamins are also necessary. Energy is also a requirement. So exactly what is your criteria for a diet to 'sustain nutrition'? $\endgroup$ – Justin Thyme Dec 10 '17 at 15:23
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    $\begingroup$ Do you care at all about soil erosion and reduced fertility due to monocropping? Growing the same crop repeatedly without crop rotation can be problematic for the long run... $\endgroup$ – G0BLiN Dec 10 '17 at 16:24
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Like Bigfoot and the Bermuda Triangle, the "complete protein" thing is a myth that arose in the 70s and lingers in the popular imagination, especially among those with an interest in promoting meat and dairy. You would struggle to get all your amino acids from a diet of iceberg lettuce, but humans can live on beans alone, nuts alone, potatoes alone and so on. https://fanaticcook.com/2014/08/11/if-all-you-ate-were-potatoes-youd-get-all-your-protein-and-essential-amino-acids/

So you could just grow one crop: potatoes. Which, as a civilization, pretty much puts all your eggs in one basket. You are at risk for famine if your one crop fails, in the manner of the Irish potato famine (yes, many other factors with that event, but they did have 1 crop and it did fail).

A deep bench, so to speak, of different crops offers insurance against failure. The other thing is you may have varying types of land available for agriculture, some suited to one crop and some to another. Dry land is good for millet and wet land for rice. Consider millet, grown thousands of years ago in China and Japan as a companion crop to rice.

https://www.npr.org/sections/thesalt/2015/12/23/460559052/millet-how-a-trendy-ancient-grain-turned-nomads-into-farmers

For ancient farmers, Jones says, millets would have held obvious appeal. "Millets are tough in various ways," he says, citing their short growing season and drought resistance. When the rains fail, a crop like wheat or rice may fail completely. But millets will generally produce something, even if it isn't very much. That gives wheat and rice farmers an incentive to adopt millets.

And millet farmers adopt wheat, rice and, more recently, corn precisely because those crops yield much more. That last point is probably the key reason why millets have lost their place of prominence in global agriculture. Wheat, rice and corn have benefitted vastly more from research and crop improvement, and commercial markets also became far less interested in "minor" crops. The end result: Many farmers who once grew a balanced portfolio of crops, including millets, have switched almost completely to higher-yielding cereals as cash crops.

"It may be time to consider whether millets have a role to play in a diverse response to crop failure and famine," says Jones.

This was more important in the old days and less so now as laid out above - with modern storage and transportation, having side crops as insurance is less important.

If you are looking for an unusual crop group for your story (I hope you are) consider the crops of the Eastern Agricultural Complex - the crops North Americans grew before maize showed up and took over. Wikipedia lists goosefoot, sunflower, marshelder, and squash among others. Weeds!
goosefoot. Goosefoot. http://joshfecteau.com/edible-farm-weeds-white-goosefoot/

If you read about these ancient crops and look at pictures, you will recognize them if you have a garden. Their degenerate descendants are everywhere. But when they were crops they were big and meaty. When the Indians switched to the Mexican crops and especially maize those crops fell to secondary status, and then were lost when those civilizations collapsed.

If you want to really do some fiction, imagine yourself in a post apocalyptic scenario and look at the weeds. You could get clues in current vacant lots, or post-Katrina New Orleans. Now domesticate those weeds into crops like out ancestors did. What would they look like? Imagine a leafy field of dandelions, each flower three feet high with seeds the size of rice grains and bitter, nutritious roots.


ADDENDUM: IS FAT A NECESSARY MACRONUTRIENT?

Judging by the comments there is interest in dietary fat and whether it is necessary. Bear in mind while doing your own research: diet arouses passion, belief and behavior like few other subjects. Superficial overviews of diet by organizations like Cleveland Clinic or Mayo or the USDA want to reassure people who are striving to take control of their lives by adopting bizarre diets. These overviews will all say fat is ok because completely eliminating fat from a normal diet will leave a potentially weird and unhealthy diet - like an all potato diet which one would not adopt except out of necessity or mental illness. Fat is ok. It is good energy, and humans need energy which must come from either fat, carbohydrate or ethanol. But except for the 2 essential fatty acids (linoleic and linolenic) fat per se is not essential. It is just energy.

Here is the USDA Essential Guide to Nutrient Requirements. I consider it definitive, at least for 2006.

There is a lot in there. But there is not a recommended daily allowance for fat (except for milk-fed infants; special case) or a minimum daily requirement for fat. For everything else one might eat, including water, protein, carbohydrate and molybdenum these parameters are given.

Page 69: The remaining chapters discuss data on carbohydrates (sugars and starches), fiber, fats and fatty acids, cholesterol, protein and amino acids, and water. In these chapters, AIs are provided for Total Fiber, linoleic acid and -linolenic acid, and water, and EARs and RDAs are provided for carbohydrate, and protein.

Page 123 Neither an Estimated Average Requirement (EAR), and thus a Recommended Dietary Allowance (RDA), nor an Adequate Intake (AI) was set for total fat for individuals aged 1 year and older because data were insufficient to determine a defined intake level at which risk of inadequacy or prevention of chronic disease occurs. However, AIs were set for infants aged 0 through 12 months based on observed mean fat intake of infants who were principally fed human milk.

The diehard might object that this guide notwithstanding, fat is still essential in the diet, but the data just does not exist to prove it. Data exists for everything else but not fat. I cannot argue with that.

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    $\begingroup$ This doesn't really answer the question. Proteins are important, yes, but they don't supply everything. And please give an example of somebody surviving on potatoes alone. $\endgroup$ – wizzwizz4 Dec 9 '17 at 21:25
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    $\begingroup$ Holy buckets, @wizzwizz4! That is why I put up the link to the site titled https://fanaticcook.com/2014/08/11/if-all-you-ate-were-potatoes-youd-get-all-your-protein-and-essential-amino-acids/. But here it is again. $\endgroup$ – Willk Dec 9 '17 at 22:25
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    $\begingroup$ @kingledion: that is true about potatoes, but we do not need to eat fats. We can synthesize fats we need. The 2 essential dietary fatty acids (linoleic and linolenic) are in potatoes. Spuds do lack B12 and so a strict potatovore might get pernicious anemia, eventually. $\endgroup$ – Willk Dec 10 '17 at 1:45
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    $\begingroup$ @Will There is such a thing as too little fat. The Cleveland Clinic's minimum recommended intake is 44 g per day. 2000 calories of potato gets you 2.9 g per day. $\endgroup$ – kingledion Dec 10 '17 at 6:13
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    $\begingroup$ @Will "especially among those with an interest in promoting meat and dairy." Hardly. That was vegetarians all the way, convincing people that they did not need to eat meat to get all their protein. $\endgroup$ – RonJohn Dec 10 '17 at 11:39
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2017-12-17 Added edit with recipes at bottom!

Grain, Root, Legume

There are, generally speaking, three major branches of staple crops for nutrition. They each And how is askinghave advantages and disadvantages compared to the others. But most regions of the world are able to grow a mix of these three groups.

All three in the mix are important. Will points out that you can live on potatoes alone. This is true, as long as you get 2000 calories a day. However, if you are short on calories with potatoes, then you are also short on protein, iron, and B1/B2/B3 (commonly known as Thiamin, Riboflavin and Niacin). On the other hand, wheat will give you a larger 'starvation margin' on those vitamins. On the other hand potatoes will give you better folate, B6 and vitamin E. All in all, its best to eat both together.

Grain crops will generally advantage you in B-series vitamins, iron and protein. They also tend to have the highest yields with the lowest work input, important in a subsistence farming society. Note there are a variety of 'pseudograins' like amaranth and quinoa that I'm going to include with the grains. Root crops are generally more protein deficient, but have a good variety of vitamins and minerals. Root crops also tend to be the hardiest, surviving in case of drought or fire or flood. Legumes generally have the best nutrition and by far the most protein, but they have the lowest overall calorie yield.

Final note: Oils and Leafy Greens

There is actually one last group that aught to be included: oils. These plants provide extra fats that are important for things like brain development in children. If you ate only a grain/root/legume you would probably starve to death from lack of fat. However, some legume do double duty as oil crops, like peanut and soybean.

Similarly you would probably die from lack of vitamin A/C/E/K. Some plants provide one of these (potatoes for C, sweet potates for A) but overall you need some vegetables in the diet to get these minerals. On the other hand, you can eat the tender green shoots of just about anything growing for some of these vegetables, so they probably aren't important enough to consider.

Possible combinations by regions of primary cultivation

Tropical Africa (old world origin only)

  • Grain: Sorghum, Pearl Millet, Finger Millet
  • Root: Yams (genus Dioscorea)
  • Legume: Bambara groundnuts, black-eyed peas/cowpea
  • Oils: Palm oil

Tropical Americas (new world origin only)

  • Grain: Maize
  • Root: Cassava, Sweet Potato (Genus Ipomea), Arrowroot
  • Legume: Common Beans, Runner beans, Peanut
  • Oils: Peanut

Mountain Americas (new world origin only)

  • Grain: Amaranth, Quinoa
  • Root: Potatoes, Yacon
  • Legumes: Common Beans
  • Oils: Sunflower (really more of North America than Mexico)

Fertile Crescent

  • Grain: Wheat, Barley, Rye
  • Root:
  • Legume: Chickpeas, Lentils, Peas, Broad Bean
  • Oils: Olive, Flax

Europe

  • Grain: Wheat, Barley, Oats, Rye
  • Root: Turnip/Rutabaga
  • Legume: Peas, Broad beans
  • Oils: Flax (Note: lack of oil crops is a big reasons Euros were so into dairy!)

NorthEast Asia

  • Grain: Wheat, Foxtail Millet, Buckwheat
  • Roots: Yams (genus Dioscorea)
  • Legume: Soybean, Adzuki bean
  • Oils: Sesame, Soybean

South Asia

  • Grain: Rice, Pearl Millet, Sorghum
  • Roots:
  • Legumes: Pigeon Peas, Chick peas, Mung Beans
  • Oils: Sesame, Mustardseed, Cottonseed

Note: China, especially south China is kind of halfway between NorthEast Asia and South Asia, and grows lots of things from both categories.

Also, as you can see, not all regions had each category

I only included things that are commonly grown now.

Pick just three

After checking out some nutritional profiles, I have two top choices:

  • Tropics: Peanut, Corn, Sweet Potato
  • Temperate: Oats, Potato, Soybean

Recipes

I was so intrigued by the concept that I decided to test it out. What would you eat with the three growable crops? I started with the tropical crops so here goes

Ingredients

  • 8 White Corn Tortillas
  • 1 cup peanuts
  • 2 Medium sweet potatoes
  • Peanut oil for frying
  • Salt

enter image description here

  • Take 1 cup of peanuts and grind with a mortar and pestle and 1 cup of water, to make a runny peanut paste. Basically, watered down peanut butter. Salt the peanut butter, and add any spices you were going to add. Also, if you aren't a peasant, just use a blender if you don't have all day.
    • Bake two sweet potatoes wrapped in foil (or a big leaf from the woods, if you're a peasant) for 1 hour. Poke some holes in the skin before you put them in the oven
  • Fill frying pan with 1/4 inch of peanut oil. When you're starting out, 1/2 inch might be easier.
  • Fry tortillas on each side for about 30 seconds; they should not get crispy. Fold them over on a plate to give them that taco shell shape. See figure above.
  • Cut up potato, divide into portions, and put into shells.
  • Spoon peanut sauce on top, and serve. See figure below.

enter image description here

I didn't want it to be too bland, so I added a couple birds eyes chilis to give it some heat, and help with some vitamin C. You could add other spices like pepper or allspice, if you wanted.

The meal wasn't too bad. It was a big heavy, and if I did it again I'd try to throw some iceberg lettuce or cabbage or something in the tacos to add a bit of crunch to it.

Bon Appetit!

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  • $\begingroup$ Another excellent answer. Thanks much! $\endgroup$ – Sundemg Dec 9 '17 at 22:29
  • $\begingroup$ @DLosc Good catch! Turnips in particular are high in calories. The others are not so they aren't really good staple foods. $\endgroup$ – kingledion Dec 10 '17 at 13:28
  • $\begingroup$ Will's comment about potatoes remains completely untrue. Your suggestions are better, but without any analysis of the exact nutrients provided this answer strikes me as little more than wishful thinking. $\endgroup$ – Jack Aidley Dec 11 '17 at 22:28
  • $\begingroup$ @JackAidley This is Worldbuilding.SE, not Nutrition.SE. If a question is tagged [hard-science] then I would have to provide references. Otherwise, you'll just have to trust that I did my homework :) $\endgroup$ – kingledion Dec 12 '17 at 1:02
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Generally, all crops have some content of minerals, vitamins, protein, sugars, and other stuff, because they need it themselves.

In your case, I would go for the most reliable and non-demanding (if you know the correct term let me know) crops. I think for a civilization, you need 4 kinds of crops--medicinal, foodstuffs, fibre and something for bio-fuel--so I will try to reflect this.

Onions and garlic

They are a natural source of antibiotics and are some of the most common herbal spices in the western world. They have a lot of vitamins too.

Pumpkins and melons

While this seems strange at first, pumpkins are easy to grow. They also can be used to feed animals and contain enough sugars to make alcohol, which can be used as a biofuel. And the hidden value of these crops is that they can be used to grow penicillin, very useful.

Beans or cabbage or potatoes

Beans are easy to grow and have a lot of protein; they are easy to preserve and store, and they also taste great. :D

Cabbage is the middle ground: not as demanding as potatoes, but still a good source of daily food. It can be also used to feed animals and is easy to preserve. Unlike other crops, you can eat it raw without any problems.

Potatoes are most versatile, but also the hardest thing to grow and preserve. They can be used to feed animals, contain a good amount of vitamins, and contain starch. You can make alcohol from potatoes. BUT it's a pain to grow them. They require intensive care, a lot of water and fertile soil to produce a good yield. It is a lot of work to plant them and then get them out of the ground. They are susceptible to blight and have many pests. They also need to change fields often, or they will rot in the ground.

Flax or cotton

Flax is more demanding than cotton, in terms of time and work, and it's harder to extract fibres out of it to make linen. But it is hardier than cotton and can grow in colder climates. Its seeds can be used for oil and for preserving wood (I don't know if other oils can do that too). Linen cloth is also said to have some antibacterial properties (but I don't know if that is a myth).

Cotton has its limitations, but is easier to harvest and process. Its seeds can also be used for oil. But it requires a lot of water.

Mulberry

While not exactly a crop in a traditional sense, it can be used for its fruits, which can be then eaten as food or processed into alcohol. It can also be used to cultivate silkworms to produce silk. Silk has the strongest fibres, good for medical and warfare applications. So mulberry checks 3 out of 4 boxes.

Oats

Oats are the most durable and most non-demanding of grains. They are also one of the healthiest. And they can be used to feed strong animals, like horses.

My personal pick would be cabbages and flax and garlic (or onions; it does not make much difference). Linen from flax can be used for padded armour and durable clothes. Flax also allows me access to oil, and fermented oil is useful for curing wood. Garlic will make the population healthier overall; it gives me 2 spices in one crop, making my food less bland, and it prevents common intestinal parasites. Cabbage can feed the masses and can be preserved in large amounts, while requiring very little preparation.

These are not all, but these will do.

Edit: Other plants from other people:

addition by - Draco18s

Kudzu

Kudzu is good for baskets and clothes(...apparently), It has some medicinal use(*TL;DR), It can not be used for oil, but according to wikipedia it can be used to make cellulosic ethanol (just like any other plant). It provides only starch, starch is not tasty, if it has some kind of taste at all, so the other crops would need to complement that. Kudzu hay is also a pain to store, because it can get wet easily, but it is great for big animals. But It is a noxious weed and it can go rogue easily, which could cause some problems, It also depletes soil quickly, if it is harvested. 2.5 / 4 good find.

I think, that Kudzu, goes well with mulberry and hemp. (Asian trio)

addition by - Jules

Hemp

Hemp provides rough fibres, that are good for ropes and bags, but they are not the best for clothes and they do not like humidity. Some types of hemp have medicinal use ;) And their seeds can processed into oil. 3 / 4 good find.

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  • $\begingroup$ Where's kudzu fall in this lineup? $\endgroup$ – Draco18s Dec 9 '17 at 22:22
  • $\begingroup$ I love the idea to look beyond nutrition and into the other uses for parts of these crops -- padded armor, durable clothes, etc. Very cool! $\endgroup$ – Sundemg Dec 9 '17 at 22:30
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    $\begingroup$ I was going to say that growing something that produces useful fibres would be helpful - flax or cotton is obviously a good choice, and there's a good reason those are the traditional choices, at least from a european perspective, but I'd suggest it's also worth considering hemp, primarily from the perspective of it being extremely easy to grow, and like flax also produces useful oil - which is good both for culinary use and for wood preservation. $\endgroup$ – Jules Dec 11 '17 at 6:39
  • $\begingroup$ @Jules And some hemp even has medicinal use. *smoke hemp everyday $\endgroup$ – Nuloen The Seeker Dec 11 '17 at 9:13
  • $\begingroup$ In regards to your first part, natural plants only have the nutrients they require themselves but while we've shaped crops this has rarely been guided by consideration of our precise nutritional needs so they're not much better. Plants also require a different range of nutrients to animals and in different proportions so this does not necessarily help. $\endgroup$ – Jack Aidley Dec 11 '17 at 22:30
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The canonical combination for a three-plant-garden would be what was called a three sisters garden - corn, beans, squash. This combination was used by Native American tribes as a set of major crops. The plants grow very well together, with symbiotic contributions, they also store pretty well (well, with winter squash and dry corn, not so much summer squash or milk corn), and they're a pretty decent staple diet.

Of course, this wasn't all they ate... the addition of meat and fish from hunting, wild and foraged foods, and other kinds of cultivated plants were used for variety, seasonings, nutritional supplements and alternatives, medicinal use, and a score of other things. And I'm sure it helped that even within this combination, there was a lot of variety to be had - different cultivars of corn, different kinds of beans or squash. But the combination of these three crops were the bulk of the agriculture for many Native American tribes, and mainstays of their diets.

In any case, I think the history of this set of crops is decent enough to make them a good candidate for your civilization, especially if more than one variety was allowed, or at least varieties with a lot of internal variation to maximize the chances of selective breeding letting them diverge into multiple complementary strains. I think it would help a lot, though, and might be within the parameters of your question, to allow your civilization to supplement these foods with hunting and forage (and/or garden medicinal plants) even if these are the only food crops.

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If your intention is that this is all they eat in a simple fashion, it almost certainly can't be done. Even with modern technology, it is extremely difficult to eat a healthy vegan diet, and especially so for young children (there have been several horrific cases resulting in malnutrition). Dietary supplements are necessary to ensure health; and that's eating a varied vegan diet with all the produce the Earth has to offer not just three. Even if you could find three unlikely plants which contain a complete set of micronutrients, they will be present in the wrong proportions. You need advanced processes to extract and prepare the right nutrients.

But feeding animals, and brewing, can fill the gap. If you instead take a proportion of the produce and feed it to animals you can then eat the animals to get a much richer, more complete, diet very easily. Brewing allows the diet to be supplemented with booze (which is nice) and, more importantly, allows yeast extracts to be made from the by-product. Under these circumstances you want a grain suitable for brewing, a tuber good for animals, and something else - probably a bean of some sort - but you're much more flexible in what you crops will suffice.

In another answer it is suggested that eating solely potatoes would suffice. This is, unsurprisingly, complete rubbish. Quite apart from the near total lack of multiple vital dietary nutrients (including vitamins A, B12 and E, and minerals calcium, sodium and selenium) which would result in malnutrition, they're also high in glycoalkaloids which doesn't matter in normal consumption but faced with the roughly 3kg/day every person would be required to chow down in order to meet their daily calorific requirements the levels consumed would be much higher and likely result in poisoning symptoms. As usual these problems would be more acute in the young than the old; it is much easier to maintain an existing healthy human than grow a new one.

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