One argument in favor of “placentophagy,” as it’s scientifically known, boils down to pretty much “But all the other mammals are doing it!” (Most of them do, anyway.) Though as anyone who’s owned a dog can tell you, not everything mammals choose to eat is necessarily a great idea. There are several hypotheses as to why animals eat their placentas, ranging from keeping predators away by getting rid of the scent to possible pain-relieving properties to ingesting some extra nutrients after birth. But we don’t really know.

Neither do we know what’s in the placenta, really. Studies have found the presence of hormones like oxytocin and progesterone, as well as iron (a nutrient oft-cited by placentophagy enthusiasts). But at what levels are these things present? Is there enough to have an effect? Are the compounds evenly distributed through the tissue? Unclear.

And would those nutrients and hormones stick around after the placenta’s been sautéd with onions, garlic, and olive oil and sprinkled on a pizza? (Just for example.) If uncooked, the placenta likely poses the same risks of infection as eating other kinds of raw meat.

While the placenta does exist to nourish the fetus inside the uterus, it also serves as a barrier between the unborn child and the environment, and bacteria and heavy metals like selenium, lead, and mercury have also been found in post-birth placentas.

The few studies done on placentophagy in humans are less than ideal. There’s one from 1954, which fed participants freeze-dried placenta and then checked on their breast-milk production. Eighty-six percent saw increases of 20 grams or more, but there was no control group. The review also states that this study did not “adhere to current scientific standards and conclusions cannot be drawn.”

Another more recent study from 2013 just looked at the self-reported experiences of women who’d eaten their placentas. Of the (almost all white) women who were surveyed, 40 percent reported that their mood improved, 26 percent said they had more energy, and 15 percent reported “improved lactation.” Ninety-eight percent said they would eat their placentas again. However, the lead author on this study was Jodi Selander, who runs a placenta encapsulation service.

The “most rigorous scientific research” that’s out there, according to Coyle, has been done in rodents by Mark Kristal at the University of Buffalo. His work has suggested that there may be a compound in the placenta and the amniotic fluid that has pain-relieving effects when ingested—but only if there are opioids already in the animal’s system. (During labor, mammals’ bodies release natural opioids, like endorphins.) This research can’t be extrapolated to humans, though.

And despite the argument that people would be joining a storied tradition of mammals eating their own placentas, the review points out that an anthropological investigation of 179 different human societies turned up no evidence of placentophagy as a cultural tradition in any of them. It seems that for humans, at least, this is a fairly modern quirk.