Most of the guts and stomach are removed. The torso is cut short below the ribs. Instead of legs there are vehicular links which the cyborg can put on and take off like a prosthesis. There are climbing versions, running versions and even choices for swimming. The arms haven't been removed, technology doesn't yet allow for perfect robotic limb precision when it comes to control, but legs are fine since walking is already automatic for most humans. By weight alone over 67% of the human is gone.

Instead of a jaw or nose there is a tungsten plate bolted to the skull, with a filtering system. The internal structure and all functions of the nose are removed and closed with bio-cement. Instead the olfactory sense is now handled by a chromatograph and breathing is done by sucking in and releasing air from holes at the side of the plate as can be observed in this image >>

Teeth, mouth bones and the tongue have been removed; communication is not a problem as the character is an antisocial who doesn't believe humans are ever worth the effort. Most leg links have a compartment where sugar and vitamin water or liquid protein can be pumped slowly into the small piece of remaining gut; alternatively in emergency cases the cyborg can dissolve nutrient pills into water and inject it directly through a feeding tube with a syringe.

The air filters can be changed and cleaned as there is a sub-mandibular opening.

When I used to work in the field, it was normal to chug down 5 or 6 one-liter bottles of water in an 8 hour period and never feel the need to get to the bathroom. Sweating was getting rid of all the extra liquids. Since the cyborg doesn't consume solid food, does that mean that it can just evaporate away all the extra weight and never need the toilet?

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    $\begingroup$ the main issue is the "waste" part. Unless you want your cyborg to prespirate urine, he or she will need to go to toilet. $\endgroup$
    – Alexander
    Commented Jul 7, 2021 at 18:01
  • 10
    $\begingroup$ A body that uses energy will produce wastes. Some are excreted through sweat, but others get scavenged by the kidneys and/or liver and need to go somewhere. Will the cyborg need a "toilet"? Maybe, maybe not. Will it still produce waste products that probably should be collected and properly discarded? Yes. $\endgroup$
    – Matthew
    Commented Jul 7, 2021 at 18:21
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    $\begingroup$ And unless you have artificial means of cleaning bilirubin, cholesterol, hormones etc from the blood and/or stopping the liver from producing bile and other associated wastes, you will have more than just urine to worry about. $\endgroup$
    – Penguino
    Commented Jul 7, 2021 at 23:01
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    $\begingroup$ The many answers are all underscoring a biological reality: cells require nutrients and generate waste. Without redesign, that waste is carried by the blood stream to the kidneys and liver for disposal. The sweat gland system isn't designed to accept and exude the waste. (If they were, the cyborg would still need a toilette... in the form of a shower to remove the waste from skin surfaces.) However, does it matter? Can't your cyborg have a waste tank that needs periodic pumping? It's gotta stop and refuel anyway, right? $\endgroup$
    – JBH
    Commented Jul 7, 2021 at 23:21
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    $\begingroup$ Note that toilette is not simply a varient spelling of toilet. It's a word with a very different meaning (though from the same root): "The process of washing oneself, dressing, and attending to one's appearance." So yes, a cyborg would probably perform a toilette now and then. $\endgroup$
    – jamesqf
    Commented Jul 8, 2021 at 4:18

10 Answers 10


The cyborg still has to break the nutrients down into forms that can be absorbed into the body. This will require not just a stomach, but some portion of intestines. These, then, will produce waste of some kind. Probably not much, relative to a typical 2,000 calorie diet of solid foods. But some.

Further, at least some liquid will need to be processed out via the kidneys and into the bladder. This will contain not just water, but the unused nutrients from the food, dead cells, and etc. This probably won't be that much different from a non-cyborg human in quantity.

The reason you didn't need to use the restroom while working in the field is that you were basically dehydrated the entire time. Not an exactly perfect environment for your cyborg.

In practice, then, your cyborg is going to need the equivalent of a colostomy bag and some sort of catheter system to handle what doesn't get digested. RoboCop could eat baby food. Which means he probably produced stuff that smelled quite similar to dirty baby diapers.

I suppose you might could drop the colostomy system if you use an IV system instead to provide nutrients. But you will still have kidneys that produce urine.

[edit] You asked in comments:

what if the liquid food is already in a form that doesn't need to be processed by the stomach?

The digestive system in summary:

  1. Mouth. Breaks food down into boluses that are swallowed into the stomach. You've removed this step entirely in your original post (OP).
  2. Esophagus. You are retaining this in your OP, but it's just a muscular tube that delivers food to stomach. (This also delivers air. Given how much of the face and neck you're destroying, you may need to also split this into two separate delivery tracts, just to prevent choking!)
  3. Stomach. This adds acid and enzymes to break down foods. Your OP posits that food entering the stomach is already at the paste-like consistency of food typically leaving the stomach. Not sure if the acids are required by your goo; probably not. Also not sure about the enzymes' necessity.
  4. Small Intestine. With additional enzymes from the pancreas and bile from the liver, this is where most nutrients are absorbed out of the food. Can't afford to lose this if you're using any kind of feeding tube.
  5. Large Intestine. Here, water is absorbed from the stool, which by the end is mostly food debris and bacteria. The bacteria synthesize various vitamins, process waster products, and protect against harmful bacteria. Again, these functions (and the bacteria behind them) are all critical if you're using a feeding tube.
  6. Pancreas. The pancreas is a busy little organ. It makes insulin and other hormones vital to life, but for digestion, it creates enzymes that break down protein, fat, and carbohydrates. These enzymes are going to be necessary, even in pre-processed food goo like you're suggesting.
  7. Liver. There are many important jobs the liver does (filtering blood for one), but for digestion, it secretes bile.
  8. Gallbladder. This stores bile. Bile is critical for breaking down fats.

So basically, if your feeding tube system delivers a constant, but controlled, measure of food into the intestines, the stomach can probably be bypassed.

But regardless, if food enters the digestive tract, some kind of fecal matter will emerge at the end of the process. This is unavoidable. You could build a system that collects it, dehydrates it, and mixes the water back into the food matter for reuse. This would lower the water requirements of your system. The waste would then be stored until servicing, where it would be turned over to whatever purpose (disposal, use as fertilizer, etc.).

You could probably remove the entire GI tract (but not the pancreas and liver), and use an IV-based feeding system. No food goo and no fecal matter. But even then, the kidneys will still have to remove stuff from the blood stream and that will have to exit the body as urine.

Again, you could build a urine-filtration rig to extract water from urine, and recycle that into the IV (or food goo concentrate). But regardless, the spice, er urine, must flow.

  • 2
    $\begingroup$ what if the liquid food is already in a form that doesn't need to be processed by the stomach? Like people who have Jejunal feeding tube surgery where the food is injected already below the stomach. $\endgroup$
    – Green
    Commented Jul 7, 2021 at 18:01
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    $\begingroup$ "Part man. Part machine. All diaper-filler." $\endgroup$
    – Tom
    Commented Jul 7, 2021 at 23:02
  • 3
    $\begingroup$ @Green unless they completely absorb everything that is injected, they're bound to have something they need to excrete through the back shaft. Urine is just inevitable as it's a byproduct of the natural detoxification of our body. $\endgroup$ Commented Jul 8, 2021 at 4:33
  • 2
    $\begingroup$ Given a biomechanical solution, you could probably make something to dehydrate the urine, storing it as a solid. Significantly reduce the frequency of needing to offload the waste, and as a solid, you could even have it as a swappable container. $\endgroup$ Commented Jul 8, 2021 at 5:16
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    $\begingroup$ @ProjectApex not even then. Much of what the kidneys excrete is waste produced by the cells after they used the nutrients, like a car's exhaust system. Even if it absorbed everything that it is injected, the only way to not have urine is to completely change kidneys and liver to something that eliminates waste in some other way $\endgroup$ Commented Jul 8, 2021 at 8:06

Here is my answer to this question: Is it theoretically possible for the human body to not defecate?

The tricky problem is bile.

If a person is fed and watered completely by vein (this is done routinely; total parenteral nutrition) the guts can atrophy but they still make mucus and bacteria still live in them. Even a person on TPN must poop occasionally.

A person might have all of the intestines removed and have the stomach be a dead end - sometimes that can happen with an obstetric catastrophe or certain tumors. The remaining problem as regards excretion is then the liver. The liver makes bile as part of its job and it is not going to stop. That bile has to go somewhere or it builds up in the liver; you get jaundiced and then eventually die. If you do not have intestines and are living in TPN there must be some route established for the bile to drain. One way is to have a drain placed.

Bile is the dumping ground for the liver. If you have a liver it needs to get rid of wastes somewhere. It could get rid of them thru a drain tube as is sometimes placed in people with blocked biliary trees. If you do not like toilets, your character could dump it in the sink.


Urine and Bilirubin

Your cyborg still needs to get rid of nitrogenous wastes (urine), which are a byproduct of basically all biological functions produced by every tissue. Ammonia is inescapable byproduct of protein metabolism, mammals convert ammonia into urea which requires far far less water to get rid of. That's where a large portion of our water goes, to dilute and flush out urine. You also have other blood born waste excreted by the kidneys that needs to be flushed as well. No matter what, if you cyborg has organic parts they need to pee. Even dialysis does not change this it just makes it mechanical instead of biological.

If it has any form of digestive tract it will still have fecal matter being produced. Even without a digestive tract it will still have minute amounts of fecal matter this will be primarily made of Bilirubin waste from the liver. this however is produced in such small amounts it could just be stored, dried and discarded as a pellet once a week or so, or alternatively dump it into your urine collection/disposal system, there is more than enough liquid to dilute it.

  • 1
    $\begingroup$ The big No here is kinda funny to me: your answer is a YES to the title of the question, but a No to the last sentence of the question text. $\endgroup$
    – TKoL
    Commented Jul 8, 2021 at 9:22
  • $\begingroup$ @TKoL It was in answer to the question at the end, I will change it. $\endgroup$
    – John
    Commented Jul 8, 2021 at 10:50

Yes your Cyborg will need a toilet.

Your cyborg gets nutrients ready for absorbtion, everything will eventually be absorbed. However your body gets rid of a large amount of waste through both peeing and pooping. For example old and damaged blood cells are filtered out of the bloodstream and put into your poop. This is what creates the brown color of poop. Without the option to visit the toilet you need some alternative to get rid of that.

Similarly many other waste products are disposed off through your piss and poop. You can't really sweat these out as that would make you a stinking, septic cyborg prone to infection and skin problems even if you wash daily. Even assuming you have some awesome anti-viral capabilities there will be a limit to what it can do, and such infections will love to get inbetween the cybernetic implants and body, disturbing the connections between them. In fact even with a great anti-viral/bacterial system it is the waste products and dead cells/bacteria that causes a lot of toxicity to build up in the body unless you get rid of it. This what the pus in wounds actually is: waste from your body and the infection which the body needs to get rid off. How are you going to get rid of that? Same method that caused the infection in the first place?

Maybe you can change what "toilet" means for a Cyborg. Some of the cybernetics seem to be able to hold food for the body, so you could simply change the plumbing and make waste products go there. It would basically be an alternative to a stoma, "easily" taken off and thrown away when it is full.

  • $\begingroup$ A stoma can work perfectly well with a remove-and-throw-away "non-drainable" collection system. (Such systems are used by humans with stomas who want to play sports, go swimming, etc.) In humans you may need a bit of forward planning, plus meds like Loperamide (the active ingredient in Immodium), to "control the flow rate" but that shouldn't be a big deal for a cyborg. (In fact, humans with stomas typically replace "drainable" collection systems every 24 or 48 hours as a matter or personal hygiene. Anyone can learn how to do it themselves after a few days training. $\endgroup$
    – alephzero
    Commented Jul 8, 2021 at 2:36
  • $\begingroup$ @alephzero I propose that at the end, but in a different more cyborg manner. $\endgroup$
    – Demigan
    Commented Jul 8, 2021 at 3:54

You produce urine from your kidney. Unless you are ok with the cyborg having regular extended time on a dialysis machine, they'll need to keep that to purify their blood and get rid of the many waste products in blood.

You also produce a fair amount of waste from protein breakdown which is normally pooped away. This is stored in the spleen as Biliverdin. This will need to be disposed of in some way as well.

You can have them work like you mostly dehydrated, but they'll be notably less efficient. It would make more sense for them to have some way of surviving if they drink a decent amount of water.

You can produce notably less poo, perhaps needing to poop once every few weeks, but you can't produce much less pee without radical changes.

  • $\begingroup$ The dialysis machine is actually a good idea - if the universe has the technology to produce cyborgs, OP can also make them have the technology to produce a filtering unit that can fit in the abdominal cavity. The cyborg doesn't have a digestive tract and the filtering unit can replace pancreas (regulating glucose), liver (filtering out toxins, breaking down old cells) and kidney $\endgroup$ Commented Jul 8, 2021 at 10:19
  • 1
    $\begingroup$ @JulianaKarasawaSouza note dialysis will not eliminate the need to pee it just means you are using mechanical means to separate it out of the blood instead of biological ones. so the cyborg still needs to pee just as often $\endgroup$
    – John
    Commented Jul 10, 2021 at 16:45
  • $\begingroup$ @John or just change a filter cartridge, depending on how many changes OP wants to do to a regular human function $\endgroup$ Commented Jul 12, 2021 at 5:32

Unless you're processing and dumping 100% of solid wastes, you'll need to get rid of it somehow. It might not be in the same form as organic waste though.

If you can efficiently remove and excrete clean water, you might be able to compress your solid wastes, minerals and other non evaporatables, and compress them into low volume cubes, you can dump them when convenient. You'd still have a significant mass savings (most things we consume are significantly water), and cubic poop isn't that usual, unless you're a wombat.



The chemical reactions used by cells to produce energy produce waste products. As such, while you can sharply decrease the amount of waste via intravenous feeding, tearing out the digestive tract, and replacing the filtering organs with a small dialysis machine, your cyborg is still going to need to expel waste in some way.

Now, as you suggested, theoretically your cyborg could expel liquid waste via the skin; there are some real-world examples of creatures that do this. However, you're going to run into three snags almost immediately:

  1. It's unsanitary. I suppose that your cyborg, being a sociopath, won't care much about the stink, but he's still going to need to take lots of showers if he doesn't want to get infections / chemical burns.

  2. He's going to go through a lot of water diluting the waste products before expelling them.

  3. Most importantly, while the body naturally expels some waste via the skin, it simply isn't designed to expel all of it that way. Such modifications would require a fundamental change in how the body works. This goes way beyond replacing biological parts with mechanical ones.


yes, he will still need to go to the toilet.

why you didn't need to pee as much as a feeble flesh-bag was because you needed to replace the water you lost by sweating, but your normal metabolism was still working normally, so your kidney were still processing the normal amount. sweat is to regulate temperature, not to purge waste.

you cyborg will still need to evacuate some waste. it's possible to reduce this to the absolute minimum if you make sure that his nutrient past is as efficient as possible, so you might need to go to the toilet less often. also, shorter gut mean less time for absorption therefor more waste.

also, you seem to over look just how much the brain consume in term of energy. it's at least 20% of your energy, so your cyborg might very well need a good portion of his gut remaining. other organs like liver and even the gut themself have high energy requirement. cutting limbs is far from enough to reduce the energy consumption to a minimum.

  • 2
    $\begingroup$ It* instead of he. Before removing its lower side, the cyborg had female getalia and the chromosomes XX $\endgroup$
    – Green
    Commented Jul 8, 2021 at 16:40
  • $\begingroup$ a brain consumes around 330 kilocalories per day, that is the 20% of the calories consumed by a sedentary person who never exercises. Construction workers or any heavy laborers need around 3400 kilocalories daily, making that 330 figure less than 10% and anyone with a sport hobby consumes a bigger amount of calories. $\endgroup$
    – Green
    Commented Jul 8, 2021 at 16:42
  • $\begingroup$ for comparison, the average drinking glass filled with pure sugar to 1/3 equals roughly 400 kilocalories. $\endgroup$
    – Green
    Commented Jul 8, 2021 at 16:43
  • $\begingroup$ plus an entire living human body needs barely 50 grams of pure proteins to heal itself, roughly 0.75 grams per kilogram of non-fat bodyweight. Since the cyborg weights only around 16 kilograms of bio matter, it doesn't need much food at all. $\endgroup$
    – Green
    Commented Jul 8, 2021 at 16:48
  • $\begingroup$ just controlled to make sure, yeah, I did mention 67% of its body is gone in the question. $\endgroup$
    – Green
    Commented Jul 8, 2021 at 16:51

Someone hinted at the answer earlier when they mentioned dialysis.

There is absolutely no need to produce faeces since you could just drip basic amino acids, glucose, vitamins, fatty acides, glycerides and minerals directly into the blood stream. The alimentary canal is only required for the absorbtion of water and the digestion of proteins to amino acids, fats into fatty acids and glycerides and complex sugars such as starch into glucose.

Respiration and normal cellular death etc produces waste protein and other products that gets metabloised to urea so dialysis would remove these from the bloodstream in the same way as a kidney does.

One thing that might mess it up (as an earlier poster said) is the disposal of bile. That's largely made up of bilirubin and other products from dead red blood cells and I don't know how you'd remove them by dialysis as the liver creates and dumps bile into the intestine via the gall bladder.


Not at all.

I knew Junior was up to something out in the barn, but it's hard to predict what notion that boy might get in his head. Eventually I just followed him in there and had it out. When he saw me he started, and almost dropped the egg. "What possessed you to take that?", I had to ask. "I want to see if we can grow our own baby cyborg..." I had to explain to him that no, cyborgs don't lay that kind of egg. How they need to wait on their master at all times, without a moment's distraction. How they pile their decorative stands high with the sterile orbs produced with their intestinal shell glands as their means of relieving themselves. I tried to keep it simple, until I noticed a faraway look as I said "uricothelic". Well, no matter. I took that egg very, very carefully out to the far drainage ditch, the one on the main road. I swear the smell lingers on to this day.


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