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In the lord of rings the elves invented an incredibly nutritious bread/biscuit, as Legolas clearly says only a small bite is just enough to satisfy the needs of an adult man for 1 day.

An adult person needs about 2000 calories per day... maybe 1600-1700 for extremely skinnny and underweight people or those who have jobs that require no physical skills. But I'm going with the 2000 calories one... obviously I mean kilocalories.

Each bite of lembas needs to sustain a person so it might give 50 grams of protein, 250 grams of carbs and enough fats to avoid protein toxicity... maybe 80-85 grams of fat can make it.

So how would a medieval society create Lembas without magic? Putting and compacting extreme loads of nutrients together is easy, the hard part is to make it edible and most importantly not deadly.

Feel free to adjust the fat-carbs-protein ratio as you prefer but please keep it healthy and close to 2000 calories per bite.

What it tastes like doesn't matter, after all is just a bite.

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    $\begingroup$ butter has 3,500 calories per pound but only 3 grams of protein take that as a bench mark $\endgroup$ – sdrawkcabdear Sep 21 '16 at 16:47
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    $\begingroup$ I've seen some stuff at the Army Surplus store that I've joked is Lembas bread. It's emergency food ration and comes in little vacuum packs about 2" square. Not quite 2000 kcal per bite, but basically a real version of it. amazon.com/Mainstay-Emergency-Food-Rations-Packs/dp/B000B43JI0 $\endgroup$ – coblr Sep 21 '16 at 20:14
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    $\begingroup$ peanut butter has carbs, fat, protein, and has been around for a while. easier to eat by the spoonful than butter, I find. $\endgroup$ – njzk2 Sep 21 '16 at 20:36
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    $\begingroup$ Legolas loves to brag about how awesome elf stuff is. Sure bread is ok, but elf bread just a crumb of that will keep you going for days. $\endgroup$ – user2547 Sep 21 '16 at 23:07
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    $\begingroup$ You may be interested in: Is Lembas (Elven bread) magical? $\endgroup$ – Möoz Sep 22 '16 at 2:59

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It just doesn't add up if you only consider real world nutritional chemistry.

The most calorie-dense food available is fat at 9 calories/gram. That's 220 grams to hit 2000 calories, nearly a quarter of a kilogram or half a pound. The volume of a closed human mouth (a clear upper bound on the meaning of "a bite") is around 45-90 cm$^3$. Lembas bread is therefore at least 2.44 g/cm$^3$ (220/90), which is nearly as dense as granite. Fat, by the way, is around 0.9 g/cm$^3$ – it floats, of course. If you assume a more moderately-sized mouth, and a healthier/more palatable composition for the lembas bread, it gets out of control very rapidly and you're walking around with bread as dense as steel.

You could try a carbohydrate based bread, but sugars are less mass-dense AND less calorie-dense-per-gram when compared to fat.

Proteins are variable but more mass-dense than fat (on average less than double), but they are far less calorie-dense than fat (less than half), wiping out the potential energy-density advantage from relying on them.

You've pretty much gotta appeal to elf magic on this one.

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    $\begingroup$ This answer at Chemistry SE (chemistry.stackexchange.com/a/34836/35161) claims that the variability of the density of natural fats is very low, and that even if you go to artificial fats you can only get to a density of around 1.3 g/cm^3, which helps a little, but in Middle Earth probably requires magic anyway. However, the answer is on a closed question, so it may not have received wide attention by potential answerers. I can't find much else on variation in the density of fats. most sources don't specify a type of fat and yet feel comfortable offering three sig figs, .901 g/cm^3. $\endgroup$ – SudoSedWinifred Sep 22 '16 at 4:02
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    $\begingroup$ @Hatshepsut solids and liquids can't be compressed much more than they are without truly extraordinary pressures. Water at the bottom of the ocean is a few percent denser than at the top. Even at the center of the Earth, with over 3 million times atmospheric pressure, iron is not even twice as dense as sitting on your shelf. $\endgroup$ – Nick T Sep 22 '16 at 6:55
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    $\begingroup$ Someone on Seasoned Advise tried to recreate lembas: cooking.stackexchange.com/questions/41332/… $\endgroup$ – algiogia Sep 22 '16 at 16:09
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    $\begingroup$ Maybe the hobbits have internal fussion reactors and can generate energy from the hidrogen in the food :-D $\endgroup$ – SJuan76 Sep 22 '16 at 21:46
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    $\begingroup$ @SJuan76 : Seems unlikely, given the number of times they eat in a day. There would also be the problem of glow-in-the-dark hobbits (from all the waste heat). $\endgroup$ – Eric Towers Sep 25 '16 at 22:31
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In the books there is a bit more wiggle room : (Farewell to Lorien; last few pages)

'Cram', he [Gimli] said under his breath, as he broke off a crisp corner and nibbled at it. His expression quickly changed, and he ate all the rest of the cake with relish. 'No more, no more!' cried the elves laughing. You have eaten enough already for a long day's march.'

So in the original a whole cake is described as being enough for a day. Also it is described as being crisp so we can guess that it's pretty thoroughly dehydrated.

Shortbread has around 500 kcal per 100g (and also fits the description reasonably well) . Even so 400g of shortbread is a lot to eat in one go but certainly not impossible.

The elves go on to say :

One will keep a traveller on his feet for a day of long labour, even if he be one of the tall men of Minas Tirith'.

This isn't quite the same thing as saying that it meets your long term nutritional requirements for 24 hours. So it's not beyond the realm of possibility that it also contains some sort of stimulant etc which helps you draw on your existing reserves immediately without necessarily replacing them. This would also explain why they encourage them to go easy on it and only use it in emergencies.

It is also noted later on when Sam and Frodo are travelling into Mordor that they notice that it seems more sustaining and moral boosting when not mixed with other foods which might back this up.

As an aside the complete inedibility of 'dwarf bread' is a recurring in-joke in the Discworld series. First appearing as a footnote in Witches Abroad and greatly expanded upon in The Fifth Elephant and Thud.

EDIT : there is a good point in the comments relating to what 'a long days labour' or 'a days march' might actually mean in terms of calories.

First is the phrasing. Does 'a day' mean 24 hours consecutively or is it 'during the day' assuming extra meals at the beginning and end of the march/work period.

I would suggest that the phrase 'keep a traveller on his feet' might imply that it is the absolute bare minimum to keep going. Survival manuals often quote 1000 calories per day as a minimum to keep active and functional (for short/moderate periods) so it's not entirely unreasonable to see 2000 calories as just about adequate for a week or so of reasonable activity.

For a real world comparison the British Army 24 hour ration packs contain around 4000 calories and weigh about 1.5kg. They are intended to provide the nutritional needs of a soldier over a period of a few weeks and so 4000 Kcal per day is probably a reasonable figure for medium terms needs for fit people doing a reasonable amount of labour. Although equally you wouldn't necessarily expect an infantry soldier to be burning through calories at the maximum possible rate for a human in this sort of period.

Having said that for something which is very clearly 'emergency rations' you could certainly keep going on a lot less that this for a few days albeit with some weight loss. If fat has around 900 kcal per 100g then even a shortfall of 2000 kcal per day is only equivalent to a couple of hundred grams of body fat per day.

The film

In the film version it's Merry and Pippin who scoff lots of Lembas but as the lore of the books establish that Hobbits have very healthy appetites but also are very hardy when push comes to shove this seems like a reasonable stretching of the point both for stylistic comic relief and to make the point that Lembas is very compact calories and perhaps a bit magical.

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    $\begingroup$ “The dwarf bread was brought out for inspection. But it was miraculous, the dwarf bread. No one ever went hungry when they had some dwarf bread to avoid. You only had to look at it for a moment, and instantly you could think of dozens of things you'd rather eat. Your boots, for example. Mountains. Raw sheep. Your own foot.” $\endgroup$ – AndyD273 Sep 21 '16 at 17:49
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    $\begingroup$ Gandalf the White : 'pyrotechnics and personal training, birthday parties a speciality'. $\endgroup$ – Chris Johns Sep 21 '16 at 18:29
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    $\begingroup$ It's the Eye of the Enemy, it's the thrill of the hike, risin' up to the challenge of our rival... $\endgroup$ – SudoSedWinifred Sep 21 '16 at 18:46
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    $\begingroup$ Someone needs to make a Frodo and Sam training Montage...:D $\endgroup$ – Chris Johns Sep 21 '16 at 18:49
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    $\begingroup$ Elven Lembas, it gives you wings? Let's see, we start with a good bread, add a lot of sugar (for taste) and caffeine... and we get a bread version of Coca-Cola. Quasi-addictive, tastes great, perks you up... but you'll need that day's march to keep from getting fat. Do I get a five cent deposit on the wrapper? $\endgroup$ – Ghotir Sep 22 '16 at 19:45
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If you want calorie density, you need fat. Fat has over twice the calorie density of carbs or protein. As long as not too much of it is saturated, you could probably survive on it.

Lets take three corners of the original vegetarian diet: whole grain wheat, lentils, and olive oil, and try to get to 2000 calories and 50g protein. Since taste doesn't matter and you have all day to digest (drink lots of water!), lets used uncooked products for maximum density.

If we combine for max energy, then 150g Olive Oil, 100g Wheat, 100g Lentils give you 2000 calories and 40g protein. You get 100% of your daily fiber, Vitamin E, Vitamin K, and Folate, and 50% of 8 of 16 vitamins and minerals I looked at.

If we combine for max nutrition, then 60g Olive Oil, 200g Wheat, 200g Lentils gives you 80g protein, 100% of 6/18 vitamins and 50% of all but Vitamin A and C, and Calcium. This combo is actually probably better nutrition than you or I get on a day to day basis, but to survive on it forever you will need a vitamin C boost to ward off scurvy, so add some tomato juice to the mix.

In any case, there are probably even better optimizations (add some tomatoes, or a little bit of meat to the mix) that would get you perfect nutrition, but the problem is the weight. Even pure olive oil is 226g to 2000 calories, and the nutritious option above is 460g...almost exactly one lb of food.

The lembas are going to have be made like a pizza crust, then hit with a shrink ray. Are shrink rays magic?

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    $\begingroup$ Hmm, whole grain wheat flour, lentil flour, olive oil (or butter?), tomato, maybe a few other seasonings and supplements, dehydrate it to reduce weight and bulk... I bet it might be made to be pretty good. $\endgroup$ – AndyD273 Sep 21 '16 at 17:55
  • $\begingroup$ Small snag, vitamin A in raw foods is nearly unprocessable. It's also a really important vitamin. $\endgroup$ – djechlin Sep 23 '16 at 22:38
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    $\begingroup$ Lembas is actually pizza? $\endgroup$ – Ber Sep 26 '16 at 19:11
  • $\begingroup$ @djechlin maybe elves ability to process raw foods without losing 100 IQ points explains why they're better at everything and don't seem to require agriculture. $\endgroup$ – Ber Sep 26 '16 at 19:12
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Complete foods are already a thing! Ever heard of soylent? They contain not only the calories, but all the nutrients you need in your RDI.

Some even look like biscuits and energy bars, like the tweenybar and this one.

Packing all those calories in a smaller biscuit or even a single bar doesn't look very feasible, and even if it was the result would be incredibly dense and hard to ingest. Maybe some ketogenic variant would be easier since some fat can store more calories for unit weight.

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    $\begingroup$ Careful with the green one though, you don't know what they put in it. $\endgroup$ – Separatrix Sep 23 '16 at 10:56
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At first glance, the math says this cannot be done. Upon further inspection, there is a solution.

A small bite is about 10 cm^3 (or 10 ml). If we want 2000 kCal, or 8MJ, this requires an energy density of 800 kJ/ml.

Gasoline is very roughly as dense as water (within a factor of two) and a quite energy dense storage medium. 1 kg of gasoline is 46 MJ, so 1 ml of gasoline is 46kJ. Off by a factor of 20.

To beat Gasoline by a large factor you are going to have trouble. Wikipedia basically tells us that using chemistry is a dead end. Explosives, for example, are not more energy dense, they just contain their own oxidizer for rapid self metabolism.

However, that same chart gives us hope. Plutonium, Tritium and other nuclear processes have insane energy densities.

The problem is that humans, or near-human things, don't metabolize nuclear fuel very well. To solve this, the elves merely have to create tiny nuclear reactors that produce digestable chemicals.

The being eats the bread, encrusted with nuclear reactor powered nanobots. These bots consume raw material in their environment and reconfigure them into higher energy states. If you don't bleed out from radiation poisoning or having your stomach lining converted into high-calorie fat, you are able to manage from very little food.

So the medieval society merely has to industrialize and generate a technological singularity, convince the resulting post-human AIs to solve the problem and help roll back every other change. Legends of such an event may remain, with the communication between the post-humans described as some kind of song.

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  • $\begingroup$ This would explain it for the elves, but what about the other races? $\endgroup$ – user2813274 Sep 24 '16 at 2:56
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    $\begingroup$ @user2813274 The other races don't have lembas bread? $\endgroup$ – Yakk Sep 24 '16 at 2:59
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    $\begingroup$ That also explains why mortal creatures in the Undying Lands wither and die. The nanobots in the soil consume them from the inside. Elves are immortal because the nanobots are always repairing them. shudder $\endgroup$ – Ber Sep 26 '16 at 19:20
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The previous answers look at the energy available in foods we know about such as fats and protein. But what is possible in terms of chemical energy density?

Since I'm leaving the kitchen, I’ll convert 2000 calories to 8.2 megajoules, so I can compare energy from other sources.

Gasoline contains 120 MJ per gallon, so 30 per quart, 15 per pint, or 7.5 per cup. So you would need more than a teacup and less than a drink can; still more than one mouthfull.

But how high can chemical energy go. This chart shows that Beryllium and Boron top the chart at 125 and 138 MJ/L. So if you could use that (with air) for fuel then about 65 ml would do. That’s a bit more than 2 fluid ounces, which is one swollow.

So it’s at least possible that some highly energetic chemical substance (plus oxygen added seperately) could provide that much energy in the required volume. All we need is the ability to make use of it. Perhaps symbiotic bacteria provide for digestion by converting it to useful forms.

I don’t like where this is going though. Creatures not adapted to it (e.g. like a cow’s stomach) can “refit” by cultivating needed bacteria in their intestines. However, they take up residence in the large intestine, which is downstream to where said bacteria can be digested and those nutrients absorbed. So a “two pass” process would be needed. After “harvesting” the converted product you will need to carefully separate the edible culture from other toxic cultures, or perhaps cook it to kill all biological activity.

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    $\begingroup$ I don't think it is possible to create completely new categories of food (in addition to carbs, fats and proteins). Those are not some random bits of molecules somehow converted by our internal reactors; they are highly specific molecules which need a lot of fitting structures and processes in your body. And not only in the stomach, but all over the place. It's not like their "energy content" is somehow zapped out of them and then electrically distributed through the body; it's the actual molecules which are transported around, stored, converted, etc. $\endgroup$ – AnoE Sep 23 '16 at 15:50
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    $\begingroup$ Even if you could invent something which is for all means and purposes neither carbs, fats, proteins or alcohol and still nutritional, then the chemical processes would still be the same (they are controlled by the body, not the food). So energy output would still likely be pretty much the same. $\endgroup$ – AnoE Sep 23 '16 at 15:51
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    $\begingroup$ With enough genetic engineering, it might be possible. The bread is composed of a high-energy, coal-like fuel and encapsulated bacterial spores that are activated by exposure to stomach acid, feed exclusively on the fuel once they enter the small intestine, and excrete usable fats, proteins, and carbs. Once the fuel is gone, the bacteria die. $\endgroup$ – IndigoFenix Sep 25 '16 at 5:56
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Portals

After reading @SudoSedWinifred's answer, most people would give up. However, I say why let physical impossibility be an impediment. Instead, let's think with portals.

Each bite of PortalBread™ contains millions of dormant nanobots. Upon contact with your stomach acid they activate, building a 1cm one-way-portal which slowly extrudes NutraGoo™ over the course of the next 18 hours.

Warning: Do not eat more than 1 bite of PortalBread™ per day. PortalBread™ portals maintain an output of 1cm^3 per hour, and never violently exceed this speed of output. NutraGoo™ has no FDA approved side effects. If you experience bloating please discontinue use of PortalBread™.

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  • $\begingroup$ Creative and all, but the question specifies a medieval society. $\endgroup$ – Chris Hayes Sep 26 '16 at 0:47
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    $\begingroup$ If they don't want Magic and they don't want science, there ain't much left. $\endgroup$ – aslum Sep 26 '16 at 0:49
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I'm going outside the box here, but what about a drug that pulls stored fat/calorie reserves from your body more efficiently? You are active and feel fine while using it, but after a while you look like an escapee from a death camp. Most of the nutrition is not in the food, and so the food energy density is no longer critical. If the food were high in calories with this drug mixed in, it would works for a while, until the user falls over and needs to recover for a few weeks/months.

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Sounds like peanutbutter shortbread cookies. Fat, protein, carbs, tasty. I think the magic is in making it palatable, and making it keep.

Also, MREs. 4000 calories, weighs < 1 lb.

Also, the lore doesn't say they're nutritious, just that they'll keep you going. So all you really need is calories.

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  • $\begingroup$ A few answers above, a MRE with 4000 cal weighed 1.5kg which is likely > 1 lb ... $\endgroup$ – AnoE Sep 23 '16 at 15:53
  • $\begingroup$ Each MRE weighs 510 to 740 grams (18 to 26 oz), depending on the menu. from Wikipedia article. This weight, 1 - 1.5 lb, matches my memories as well. MRE's aren't designed for long term survival. High calorie, high in salt, low in vitamins and other nutrition. Living on a steady diet of them would leave you obese, hypertensive and likely well on the way to diabetes or heart disease or both. Plenty of calories to keep you going though, for a week or even more. $\endgroup$ – Xalorous Sep 26 '16 at 20:18
  • $\begingroup$ @Xalorous -- All MRE diet means seriously constipated too. $\endgroup$ – Gary Walker Dec 21 '17 at 20:04
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Protein toxicity is not a concern in healthy people, as you can read here. Furthermore, 50g of protein per day is nowhere near enough to cause toxicity in a renal-impaired individual unless they had less than ~20% function. The presence of other macronutrients is irrelevant to elimination of protein metabolites. A person can survive for a long time on a protein-only diet, not that I'd recommend it. Amino acids are regularly converted to glucose, resulting in ammonias and other wastes which are eliminated through urine or through the pores via sweat. The belief that a protein-heavy diet places harmful stress on the kidneys has been largely disproved by recent studies and the anecdotal evidence of millions of healthy athletes.

Your best bet using nonmagical medieval tech is Pemmican, though it would need modification from the traditional recipes to better provide certain minerals and vitamins. Bread would likely mold or grow stale rather quickly, whereas Pemmican will keep for literally decades if properly sealed.

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I know this is way too late, but it is possible to have specific molecular structure of fat acids to be much more dense that the regular fat. Now add some handwaviumy perfection for that structure to be split in stomach and you are done.

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It’s not about calories, it’s about how your food can sustain a person.

According to Energy in natural processes and human consumption there is roughly 3824 kilocalories in a pound of coal. Which should be definitely enough to sustain a person, but woe to the person who decides to live on a diet of coal.

The caloric content is only a piece of a process which depends a great deal on the bodily chemistry of the individual and the bodily chemistry of the species (no Leopards on a diet of bamboo leaves, but Koalas seem fine).

The exact mechanic of sustenance by food is still not discovered. There are also no foods known which have been observed to sustain “average” person on a single bite a day. There are allegations of people fasting for prolonged periods of time or living off minuscule amounts of food for even more prolonged periods of time, mainly attributed to exceptional attributes of such people.

As far as writing fictional stories goes, you are better off letting yourself invent any superfood that you like. If you want some realistic examples, there are probably none available, but you might come up with realistic-sounding stuff.

Taking as an example, whey protein powder at 150 calories per 40 grams, you’ll need to have 533 grams of whey protein powder to satisfy your requirement. That’s quite a lot, even if you are successful at compressing it into a small chunk. Maybe if you churned a pile of maggots, dissolved the mush and precipitated the protein, cleaning it thoroughly, you could get more energy-dense matter, then possibly compact it into small form-factor, maintaining its solubility or brittleness so it would be easy to consume, you could get into one-bite volume.

Ideally, you will be after a foodstuff which does not result in waste production when put through the digestive system, i.e. is consumed completely and utterly.

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  • $\begingroup$ "in a pound of coal. Which should be definitely enough to sustain a person". This leads us back to Terry Pratchet's Dwarf Bread; rock-like and highly nutritious but no one in his right mind would want to actually eat the stuff. [wiki.lspace.org/mediawiki/Dwarf_Bread] $\endgroup$ – Mark Ripley Sep 25 '16 at 6:41
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The Lembas bread is based off of Pemmican, guys. Probably going to be the closest thing you can get. Which is actually pretty damn close lol. And yes, I do realize i revived a dead thread lol.

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  • $\begingroup$ Welcome to Worldbuilding, Some guy! If you have a moment, please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods, and how we do things here. Have fun! $\endgroup$ – Gryphon - Reinstate Monica Feb 3 at 18:58
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    $\begingroup$ SE is not a discussion forum. Please provide something to back up your answer, such as a measurement of the calorie content of pemmican. As it is, this answer is not very high quality. $\endgroup$ – Gryphon - Reinstate Monica Feb 3 at 18:59

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