Dear All Science Fiction Authors Everywhere,
I realize that it's a classic science-fiction trope that is rich with thematic possibilities, but it's not sustainable, long-term, to use human beings as food. You see, meat is not actually a very efficient use of agricultural resources; you use more grain in fattening an animal to the point where it can be eaten than you get from that animal. In other words, a typical cow...or to be more germane, a typical person...consumes more than 200 pounds of food in the course of their growth to a 200 pound person. Even if you assume that our hypothetical dystopian cannibal overlords are like Native Americans, and make use of every single part of the human being, they're still wasting resources. It'd be cheaper and more efficient just to feed them the grain in the first place. (And if you don't have grain available for some reason, like, say, the Earth is enshrouded in a perpetual cloud cover, the laws of thermodynamics say you're pretty much screwed.)
The main reason you hear about isolated groups of people turning to cannibalism is that those people are already full-grown adults, looking to eke out as much time as they can from their existing food supplies; the food costs of fattening a human being up has already been paid, and doesn't need to factor into their calculations. But as a permanent survival plan? Sorry. It just doesn't work. (This is why, when I had to come up with a "mysterious processed foodstuff" for Feng Shui, I used seaweed and rats as my ingredients. Just as icky, far more common.) So please, let's not see this trope again, save in outright comedies (Futurama's use of Soylent Green as an Iron Chef ingredient was hilarious, for example.)
Thank you in advance for your co-operation.