Argthtjtr

In the grim darkness of the far future, there is only war. The world has become a barren wasteland that is inhospitable to the the human race, which has been forced to take residence in hive cities. These are massive industrial metropolises that are densely populated and built deep into the Earth's crust. This has been the case for thousands of years, and the human race now number in the hundreds of trillions. As a result, these hive cities are overpopulated and resources are always in dangerously short supply. However, one invaluable resource that is always plentiful: bodies.

The hive cities make use of every available resource, no matter how grim. The bodies of the dead are not buried or cremated with respect, but processed into a paste called corpse starch. This nutritious paste is broken down human remains mixed in with various ingredients, which are then fed to the starving dregs of society. Practically, billions of people die every day. People who have died of natural causes or accidents from unsafe working conditions, executed prisoners, unwanted children who have disobeyed their parents too many times, etc., will all be turned into food to feed the living workers and the armies that keep hive cities safe. This is so the nobility can save the real food for the important and relevant higher-ups of society.

Of course, the kind and benevolent leaders of the hives hate having to take this route with the masses, but it is a regrettable sacrifice that must be made for the survival of humanity. With heavy hearts, they have taken it upon themselves to design a system that processes bodies into food that maintains the nutrition of the population? How can I make this work?

NO

Can you feed the entire population? No, you cannot grow enough new bodies on dead bodies to feed existing bodies, its a closed loop which will not work in biology (or physics). You must have a large source of fresh energy and resources.

One adult corpse has around ~100,000 calories (assuming you eat everything), the average person needs ~2000 calories a day, that means with perfect recycling one corpse can feed someone for 50 days. But it takes 7300 days for a human to reach breeding age. So you still need to feed said person for 7250 days with something else, and that's if they die at age 20.

So under perfect conditions corpses can provide 0.7% of your populaces caloric needs. Recycling corpses does not provide noticeable benefits, your rich folks are just screwing with your poor people.

If you feed the people nothing but the dead, you need seven and a half corpses per person per year, (that's a negative 214% decay rate) If you start with 10 trillion people the last person will starve in 14 years. Keep in mind an industrial civilization is expected to collapse if it looses more than half its population which will happen in the first year. So in this case your aristocrats were beaten to death and fed into the machines in the first year by a massive angry mob.

Sounds like your looking for a way to throw people into a meat grinder and make ground beef.

And you know what, that's is what you need to do.

First though, just like with cattle, the human needs to be checked for diseases.

Assuming they don't have mad human, they can have their bowels removed, possibly deboned, and tossed into a giant meat grinder. Might be a good idea to smoke the meat like ham before packaging and selling.

If your looking for problems with this though, almost everyone has a disease of some sort, and many can spread through the stomach. So this is likely to just make your sick and weak people sicker and weaker still. Eating tainted food doesn't make you healthier.

And to expand on the mad human, @Luke has a great explanation

Cannibalism greatly increases your risk for prion diseases. Prion
diseases can develop spontaneously (e.g. sporadic fatal insomnia) or
as a result of a genetic variation (e.g. fatal familial insomnia), and
cannibalism would spread these diseases to more people. Mad cow
disease became an epidemic because the cow's food was contaminated
with cow remains. Because of this, the risk of supplementing a
population's diet with corpses is very great indeed.

This is also only a temporary solution. It would clean up the immediate dead bodies lying around, but a human body contains roughly 125,000 calories, at 2000 a day that's only 62 days. So you could feed your starving people for 2 months assuming there was 1 dead body per starving person. After that, the food runs out.

Pretty sure this would violate the law of conservation of energy.

I'm pretty sure you and the people who made the matrix had the same idea (remember, humans are used as batteries and the dead humans are recycled to feed the live ones).

The matrix would never work because that assumes that you can always run at 100% efficiency, which is impossible. You have an even thornier problem in that you need humans to be productive members of society, so your conversion rate would be way less than 100%.

You could always pull a "Soylent Green" where meat is so rare that people are willing to by "Soylent Green Meat" without asking too many questions.

Cannibalism Alone Cannot Support Any Species For Long

It's just mathematics, really.

Creatures gain or lose weight by a simple formula: energy in - energy out. Humans lose weight by either increasing exercise (more energy out) or decreasing caloric intake (decreasing energy in).

There is no way to get energy out to equal 0 short of something like cryosleep. How low you can get this energy varies greatly from species to species, but mammals can't get very low and still survive. This means that, just by the process of living alone, humans burn energy. A lot of it. Every movement, every breath, every heartbeat is energy you got from eating a corpse that somebody won't get by eating yours.

Life needs a constant influx of energy to survive. On Earth, that influx of energy comes from the sun. Plants get energy from the sun, animals eat the plants. New energy to Earth. If you cut external energy sources out of the food chain, your food chain will collapse extremely quickly and there's nothing you can do about it.