Bizarre 2011 Live Science article ignores moral concerns, and looks at cannibalism from a disturbing scientific view:
"…the most-sensible first choice for meals might seem to be the elderly. After all, a fifth of those 10 billion humans will be at least 65 years old, and less physically able than the rest to contribute to what remains of society.
Part of the problem is that humans are just not very meaty compared with cows, pigs, deer and other animals. Even if we heavily supplemented our diet of human "long pork" with grains, we'd have to consume more fellow humans per year than we could ever hope to replace with new babies.
Based on numbers from Vogel's book "Prime Mover: A Natural History of Muscle", a human body on average can provide around 45 pounds of slightly fatty meat and other edible parts. (An all-meat diet, if organs are consumed as well, can supply all the body's nutrients, as demonstrated by Eskimos.)
Those victuals translate into about 60,000 kilocalories. Humans need 2,000 to 3,000 kilocalories a day for sustenance. (The "calories" listed on nutritional labels are actually kilocalories.) Assuming there was barely enough chopped-up man-meat to go around and the cannibals were getting only 10 percent sustenance per day based on a 3,000-calorie diet, a single person could provide 200 days of sustenance to the person who eats him."
livescience.com/16779-soylent-green-real-life-cannibalism.html