According to archeological evidence, the real Paleo diet included some human flesh now and then. But as Ars has reported before, deciphering exactly why our ancient relatives dined on their fellow hominins is tricky and up for debate—was it for rituals, other social reasons, or just good eats? A new study counting up the calorie content of a Paleolithic diet—and human flesh—suggests that cannibals were not thinking with their guts.

By rough estimates, eating all the skeletal flesh off a human—not including the organs—would provide about 32,376 calories . An optimally sized hunting group of 25 male Neanderthals or Pleistocene adults (anatomically modern human) could get about a meal out of that. But if the same group tracked down a boar or cow—which are less cunning and maybe easier to hunt—they’d have three days' worth of meals out of the skeletal flesh. The findings appear Thursday in Scientific Reports.

“On a nutritional level, hominins fall where expected, in terms of calorie content when compared to fauna [animals] of a similar body weight,” the study’s author, archeologist James Cole of University of Brighton, concluded. “However,” Cole went on, when you compare them to the large animals we know our ancestors also ate, “the calorie returns of individuals and groups of hominins are significantly less” than going after that bigger game.

Outside of desperation during famines, the explanation that hominins were cannibalistic for nutritional reasons doesn’t hold up, Cole suggests:

Rather, given the apparent scarcity of cannibalistic behavior in the archaeological record within individual hominin populations, coupled with a picture of increasing social complexity from hominins during the early Pleistocene onwards, it is more likely that the motivations for cannibalistic episodes lay within complex cultural systems involving both intra-and inter-group dynamics and competition.

To get to that conclusion, Cole had to do some gruesome nutritional calculations. Using published chemical compositions of four human males (Homo sapiens), he calculated the average total calories from fat and protein in every bit of the human body. If a cannibal ate the whole thing—from the muscle to the lungs, bones, and skin—they’d get around 143,771 calories. Fatty tissue was unsurprisingly the most calorie-rich portion, weighing in with 49,939 calories. A meal of human liver, sans chianti and fava beans, offers about 2,570 calories—that would be a nice day’s worth of calories for the average modern adult male, who eats about 2,400 calories a day.

(Archeological and other evidence does point to cannibalistic hominins eating organs. But that calorie total is still less than half the calories from just the skeletal flesh of a cow or boar.)

Brutal dinner parties

Because archeological sites suggest that non-adults were also consumed, Cole then calculated calorie contents of male human infants, children, and teens, based on size. Eating an entire baby offers about 12,823 calories, he found. Sadly, he couldn’t estimate similar calorie contents for female hominins—he didn't find published chemical compositions for them. And, he noted, “the collection of primary data of this nature was outside the ethical (and legal) scope of this study.”

Using the male estimate, Cole could then roughly calculate the total calories consumed from skeletal muscle or whole bodies at nine different archeological sites that had evidence of cannibalism. For instance, in Gough’s Cave in England, bones dated around 14,700 years ago at the end of the ice age suggested that two adults, two teens, and an infant were eaten, possibly for nutritional reason. If diners ate the whole bodies, they would have had 519,559 calories total. If they just stuck with the skeletal muscle, they would have gotten 114,773 calories.

Still, the effort of hunting down humans doesn’t seem worthwhile when bigger, potentially easier game of mammoth, bison, cattle and horse offered so much more calories total, Cole argues. “This return must therefore question the viability of hunting and consuming hominins for strictly nutritional reasons,” he concludes. He suggests to his peers that his nutrition information be included in future, holistic interpretations of cannibalistic episodes of the past.

Of course, his study does have some gaps, in addition to the lack of female data. The calories were calculated based on Homo sapiens, so there is likely some variation among hominin species—not to mention individual-to-individual variation. It’s also unclear how cooking human flesh might alter the nutritional content exactly. And of course, there’s no accounting for taste.

Scientific Reports, 2017. DOI: 10.1038/srep44707 (About DOIs).