Objective: Replace the human digestion apparatus (stomach, guts etc)

From my basic understanding the human body needs food, because it needs ATP (energy unit, some kind of sugar(?)) or you could say high enough (but not too high) blood sugar at most points in time, correct?

Assume you have sufficent technology to rebuild greater parts of the human body (extract organs, rebuild pathways etc), with what would you replace the digestion apparatus?

-> The mouth would be used to talk and breath, nothing more.

What would a theoretical device inject or introduce into the human body?

a Minor idea by me:

Use enriched blood with everything the human body needs. A device enriches the blood by "sci-fi" means and introduces this blood back into the bloodcycle.
- The logistics may be a challenge, the device would need a store of vital substances.
- An energy outage would result in quick starvation / brain damage

Would the blood idea be feasible? Do you have a better proposal?

Aspects to ignore:
-> Eating like we do now is obviously the more flexible approach
-> We need to chew etc. to prevent teeth / jaw detoriation.

You have far-future tech to fulfill this objective.

-The objective is also to make the logistics (for the food recipent) of the whole process as hassle-free as possible. Something like public food pellet dispensers.
- the method of feeding is actually a limitation for the main character to overcome, having undergone this modification "not entirely" voluntary :).

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    $\begingroup$ "The mouth would be used to talk and breath, nothing more." I'd hate to live in such a world. $\endgroup$ Nov 22, 2018 at 17:24
  • $\begingroup$ By the way, we don't eat just for energy. You are quite literally what you eat. $\endgroup$ Nov 22, 2018 at 17:25
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    $\begingroup$ What you are talking about is basically off-loading the digestion system to an external machine/creature. It digests and absorbs the food and creates a foodsource that is the easiest to absorb into the bloodstream, if not creates blood with the nutrients inside which is directly injected into the bloofstream. If you want to really replace it with something on the body itself rather than externally you need a different idea. $\endgroup$
    – Demigan
    Nov 22, 2018 at 17:31
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    $\begingroup$ You will not die fast with no power. It takes weeks-months to starve to death. $\endgroup$ Nov 22, 2018 at 17:34

2 Answers 2


What humans need is a certain mix of chemicals. I'm not going to list all that science has identified, but they include all the commonly known nutrients.

Medical science has already developed means (and substances) to feed patients intravenously, bypassing the digestive tract. This is called parenteral nutrition.

What humans without a digestive tract would probably do is insert containers with a nutrient mix into a compartment in their bellies in the same way that we change batteries in an electronic device. From there this nutrient mix would be injected directly into the blood stream.

The energy for the mechanism that transfers the nutrient mix from the container into the blood would come from the body itself. Digestion in humans needs energy (that's why people are often mentally and physically tired after a meal), and that energy is now free to be used by this biomachine. It could work by changing the digestive muscles to pump the nutrients into the blood, instead of moving the food through the bowels.

  • $\begingroup$ Wouldnt it be easier to shortcut this and implant full fatcells straight into the body? Its basically what eill happen to the nutrients anyway. Have a few alternative cells with the remaining nutrients and chemicals you need that arent stored in the fat cells and you are done. $\endgroup$
    – Demigan
    Nov 22, 2018 at 18:29
  • $\begingroup$ @Demigan That will probably depend on what is easier/cheaper to produce, what is easier to store (can fat cells be cooled without taking damage?), and so on, all of which is beyond my expertise. $\endgroup$
    – user57423
    Nov 22, 2018 at 18:31
  • $\begingroup$ considering what is asked I doubt technology limits is going to be a problem. Considering we can already 3D print a simple ear, technology at the time of OP would likely be able to print entire bodies, assuming its possible some day. Keep the cells "fresh" in a host-body that just consists out of whatever that created the fat cells, as what can create it can supply the nutrients to keep them alive $\endgroup$
    – Demigan
    Nov 22, 2018 at 19:25
  • $\begingroup$ @Demigan Technological limits are necessary for stories to be thrilling. If everything is easily possible, then there are no problems for the hero to overcome. So it is better to create a world with some inherent limitations. $\endgroup$
    – user57423
    Nov 22, 2018 at 19:31
  • $\begingroup$ no limits to the specific biotech then. You dont need to limit something you want in just to force an inherent limitation if that limitation can be somewhere else. IE, "the people dont need food anymore 'cus cool tech. They are trying to solve murder/overthrow Evil government/stop pirates/save princesses/find the mcguffin/whatever". $\endgroup$
    – Demigan
    Nov 22, 2018 at 20:03

Most of the food we eat is actually processed by bacteria in our guts. We would die without those bacteria. Sometimes people who take a lot of drugs lose the "friendly" bacteria in their guts, and they would have to re-introduce that bacteria into their guts using a process I'd rather not mention considering today is a food-related holiday. The machine you're thinking of would be some kind of glorified food chopper that can break down food into tiny pieces small enough for the bacteria to process into nutrients.

Now, even if a machine can reproduce the functions of a digestive system and its colonies of bacteria, humans would still need an organ like the liver which can create glucose out of stored fat cells. The process is called glycogenesis.


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