Inedia - cessation of intake of food and water
Inedia is the belief that one can sustain themselves on prana alone. Prana being some etherial magic energy able to sustain a person instead of calories. Western advocates during the New Age movement reffered to it as breatharianism.
Now this isn't the same as fasting which is also a spiritual practice. True practitioners are said to cease eating and intake of water altogether for the rest of their lives. There are a number of well documented and researched cases.. of course the durations of those lives were short. The ideas is kept alive by claims of Gurus and spiritual leaders who refrain from any study demanding constant observation. So yeah. It's not only bullshit.. but it's bullshit that kills psychologically vulnerable people.
The biohacked version of course requires no faith and only 12 units of magical Prana. So cats don't eat fruit. I'm not heavily involved in the genetics stuff but around 60 million years ago, some proto-mammal that was our ancestor lost the
l-gulono-lactone oxidase (GLO) gene allowing ascorbate synthesis from glucose. So we need to eat vitamin C to survive, while other mammals like cats do not.
There are other related concepts that might apply here like the amino acids that we make but still need dietarily. Nearly everything in diet essential to life is created by other organisms. The exceptions being trace minerals, water, and O2. So the genes and pathways to create all of the vitamins already exist. In itself, this still isn't breatharian. Even if we had pathways and mechanisms (Think chloroplasts).. I doubt we even have the surface area to live off of sunlight. Maintenance of body temp alone costs more then that. But what is we could live off of carbohydrates alone?
My thought here still comes down to inefficiency. I mean, sure we could create all the amino acids from raw parts and glucose. We already do it for 10 of them. But it's a kind of inefficient pathway I think? Maybe the amino acids cost of maintaining all the machinery is higher then it's output. I haven't seen any experiments adding metabolic pathways to complex organisms. Thoughts?
Perhaps in the future, we'll be a whole society of GE tardigrades. Or perhaps we'll live in luxury and repress the engineered caprophile class.
There are lots of experiments adding metabolic pathways to organisms, of all levels of complexity.
The term you want to search for is "metabolic burden".
Also, you can't live off of carbs alone. It's not as simple as fix this one "inefficient" (implies you understand who the organism works in in entirety to make that claim btw) pathway that does a thing that is done other place that you want but don't actually understand why there was a trade off to begin with....
Anyway, all that aside, it isn't conceptually impossible. There are papers on it already available.