OK, let's just make this clear up front: Medical Daily does not endorse cannibalism in any form. Not even a taste.
But if you're curious about the nutritional value of a human body, like Popular Science was (weirdos!), there's actually a good bit of research on the topic, written by Dr. James Cole, an archaeologist at the University of Brighton in England. Cole is interested in the origins of the human species. And no survey of human origins is complete without confronting the yucky fact that, occasionally, we used to eat each other.
"It is no surprise that little or no previous work has been done on determining the nutritional value of the human body," Cole writes in his 2006 dissertation, "Prehistoric Cannibalism: An Act of Nutritional Necessity or a Result of Socio-Cultural Conditions?" The paper is like it sounds. Cole wanted to know whether early humans ate each other for cultural reasons (religion) or because they were hungry. When he turned to the existing literature, he found a key piece of evidence was missing: From a dietary perspective, does it even make sense to eat humans?
The short answer is that sometimes it makes sense. Humans don't pack the same caloric yield as, say, a bear, which was another option for prehistoric hunter-gatherers. So a group would have to eat at least three people at a time to make it worth it. Of course, if you slaughter your own, you wouldn't be much of a group after a while. Exocannibalism — eating people outside your group — makes for difficult hunting. So you can start to see the cost-benefit analysis that goes into putting humans on the menu.
Before Cole's research, there was apparently only one other attempt to conduct that analysis. In 1970, Cole writes, a pair of anthropologists tried to count the calories of a small man. They figured a guy who weighed 110 pounds has an edible muscle mass of about 66 pounds — 18,000 calories worth of food. They estimated that was enough to feed 60 people for one day, and therefore they'd eat through the available population pretty quickly. Their math seems fuzzy, but they ultimately ruled that, no, cannabilism was for ritual's sake, not hunger's.
Cole wanted to get a little more scientific about it. He defined the different edible body parts of an anatomically modern adult male and then calculated the calories of each part based on their weight, fat, etc. A thigh was 10,707 calories, a heart was 722 calories, skin was 8,294 caories, and about half of all the calories (more than 40,000) came from adipose tissue, or fat. All told, if you eat a grown man, you'll consume 81,472 calories, Cole says. (But don't do that. Seriously. And if you do, do not say Medical Daily said it was cool.)
Even though that sounds like a lot, our ancestors could probably find better sources of food. On the other hand, Cole points to a bunch of dig sites where the remains of cannibal victims were discovered. In each case, three or more people had been consumed, suggesting that the cannibalism was "nutritional" rather than "ritual." Meanwhile, many instances of ritual cannibalism are known, including the headhunters of Papua New Guinea, who ate rival warriors to maintain universal order. Meanwhile, Anthony Hopkins just likes the taste.
Source: J. Cole. Prehistoric Cannibalism: An Act of Nutritional Necessity or a Result of Socio-Cultural Conditions? Academia.edu. 2006.