Here is the setup: Elves, through magic, have the ability to cause regeneration of limbs/healing of wounds through natural cellular processes. Regenerating a limb, while now possible, obviously takes a massive amount of energy. Either that, or a really, really long time.

How can I get the necessary energy packed into a fruit, which is at the most, the size of a large mango (the smaller the better - more convenient to carry around)? I'm basically trying to have a fruit that the elves can eat while healing, which will speed up the healing process.

What I need is composition. Would it be based in carbohydrates, like a potato (which I realize is not a fruit), or somehow high in protein (maybe from a carnivorous plant)? Which one would pack more punch for healing? Would the contents have any effect on the skin and/or meat of the fruit? If so, in what way? What about the plant itself?

  • $\begingroup$ Immediately after posting this question, ideas are forming about a massive strangler vine that constricts gigantic prey, and then puts a large part of the protein acquired this way into an underground bulb for storage - basically a protein potato. This would actually be very ideal, but I'm not sure how said protein potato would turn out. $\endgroup$ Commented May 9, 2015 at 1:14
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    $\begingroup$ You can assume so, but why not just eat meat? If data given by knave are correct and your magic allows for 100% effective transformation of tissues, the injured person has just to eat two rabbits with bones (or their equivalent). On the other hand, your plant can transform it into one big "potato" (or many beans, as JDługosz suggested) rich in proteins, calcium and other nutrients that can be eaten in one or a few days. If I were @knave, I would include it in my answer. $\endgroup$
    – BartekChom
    Commented May 9, 2015 at 9:13
  • $\begingroup$ for raw calories you want fats. $\endgroup$
    – John
    Commented Apr 3, 2023 at 21:12

4 Answers 4


Forget energy and nutrients- If you want a new arm, you need the weight of a new arm, in raw materials. A bit of Googling shows figures ranging from 5-6% of your body weight in one arm, which is about 8 pounds. So in order to grow a new arm, you need to eat eight pounds, which is way more than any normal person can handle. Eight pounds is about the weight of two rabbits. But it doesn't stop there: There's roughly 1.3 pounds of bones in your arm, so you would have to eat 1.3 lbs of bone, which your body would then have to break down, move, and reassemble.

It would be far, far better to get your original arm back and tie it in place while the magic healing reattaches it. Or at least find a more efficient way of getting the raw materials than through the stomach.

Of course, this is only relevant if your magic doesn't break conservation of mass. But if it does, all bets are off.

  • $\begingroup$ From exrx.net/Kinesiology/Segments.html-> 5.7% to 4.95% for a full arm $\endgroup$ Commented May 9, 2015 at 4:26
  • $\begingroup$ I rounded a little. The numbers I used were 8lb / 140lb = 5.714%, and 23lb skeleton with the same percentage. A few tenths of a percent don't change the conclusion that that is way too much food. $\endgroup$
    – evankh
    Commented May 9, 2015 at 8:29
  • $\begingroup$ But… this doesn't answer the question. $\endgroup$
    – o0'.
    Commented May 9, 2015 at 10:11
  • $\begingroup$ I like that, but if we are going into atom-transforming-magic maybe it could use some O2, N2 and CO2 of each breath you take? $\endgroup$
    – SJuan76
    Commented May 9, 2015 at 19:12
  • $\begingroup$ @Lohoris Sure it does. The "fruit" would have to be made out of 8 pounds of meat and bones. $\endgroup$
    – evankh
    Commented May 10, 2015 at 2:08

Instead of looking at the fruit as an energy source, why not have the fruit transform its eater into a more efficient energy manager.

For a half day following consumption, every resource in the eater's body dedicates itself to healing. Consciousness retreats and body temperature plummets, leaving the patient motionless and prone. Hours pass during which body fat dissolves and flows toward the wound. Healthy muscles and bones sacrifice their mass as well. Before the process began, the victim was a one-armed he-man. Afterwards, he's a 98-pound weakling, but he's got two arms.

In an Elven care center, the patient would feist before on high protien foods, marrow and high energy beverages. This would serve to minimize the the loss of muscle and bone. When travelling, the elves might still carry the fruit for emergencies, but they would be very hesitant to use it because of the cost.

Small quantities of the fruit could be used to heal smaller cuts with a propotionally slower cost to constitution and health.


Per unit mass, fat has the more than twice the energy of the other two (carbohydrates, protein, and fats). Fats contain 9 cal / g. A dietary calorie = 1 scientific kcalorie. A mango normally weighs about 500 g but let's say the fruit we wish to use is twice that (1000 g). The most energy you can put in your fruit is $ 1000 gram \times \frac{9 calorie}{gram} = 9000 calories $. In this case, it'd simply be a massive lump of lard.

Our bodies preferentially burn carbohydrates for energy and require proteins for cellular construction, so you'll want to dilute your fruit with these other components.

The bar must also contain the micronutrients essential for the healing, probably in proportion to our regular needs for vitamins and minerals but at increased amounts.

All in all, you probably need a fruit composed of all the things we normally need in our diet and approximately in the same proportions as our diet requires. If you weight it a little heavy with fat, then you'd get something like:

  1. 350 g ~ 3150 calories fat
  2. 350 g ~ 1400 calories protein
  3. 300 g ~ 1200 calories carbohydrates
  4. A few g micronutrients

Modern technological humans discovered a need for concentrated nutrient foods for people with ill health, have problems with digestion, or who are malnourished. You can find this food in your grocery store under the brand name $ Ensure^{TM} $ (among others).

What I see in this 237 g bottle is:

  1. 6 g ~ 54 calories fat
  2. 9 g ~ 36 calories protein
  3. 40 g ~ 160 calories carbohydrates
  4. 1 g or so of micronutrients
  5. ~180 g of water

Your fruit would probably have a similar composition.

From personal experience I can also assert that if your fruit is too nutrient dense, it will cause digestive issues as it pulls water out of your body and into the digestive tract through osmotic pressure.


You are thinking of beans. I understand that is the source of protein in a vegetarian diet.

Why need a giant bean? A handfull of beans or nuts would work just as well and can be eaten incrementally.

Look for foods that are high protein and low fat, and breed (magically engineered) to be more optimum for the task.


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