If certain corners of the parenting Internet are to be believed, the benefits for a new mom of eating her placenta are manifold. Staving off post-partum depression is a biggie, as is helping with milk production for breastfeeding. Others say it gave them “tons of energy.”

The practice seems to have had a minor resurgence in recent years, thanks in part to celebrities like Kourtney Kardashian and January Jones who have publicly endorsed it. For those who don’t want to just chomp into the raw tissue like Daenerys Targaryen eating a horse’s heart, the Internet provides recipes for smoothies and spaghetti. Dehydrating the placenta and encapsulating it into pills is perhaps an easier-to-stomach method (and Kardashian’s method of choice).

In the hopes of injecting some science into all this, researchers at Northwestern University did a review of the existing literature, published Thursday in Archives of Women’s Mental Health.

“A lot of people are citing these studies as support for the benefits, and we wanted to take a more scientific look,” says the lead study author Cynthia Coyle, a clinical psychologist and health-system clinician at Northwestern’s Feinberg School of Medicine. “There really are no human studies based on today’s scientific standards to actually show as evidence for human effects, and the animal studies aren’t translating into human benefits.”

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.

So what’s driving it? Besides celebrity endorsements, that is.

“This is speculation, but there has been increased awareness on the prevalence of postpartum depression and other difficulties that women have after giving birth,” Coyle says. “Maybe due to shame or embarrassment, there’s ambivalence about taking medications during pregnancy and nursing. And I think the way supporters present it is that it’s a natural remedy and if all animals are doing it, why aren’t we? And I think that’s driving a lot of women.”

Coyle says that this new study was inspired by a call that co-author Crystal Clark received from one of her patients at Northwestern’s Asher Center for the Study and Treatment of Depressive Disorders. The caller wanted to know if eating her placenta would interact negatively with her antidepressant medication.

“We were trying to raise awareness among medical providers so they have the knowledge of the science that’s out there, what’s known and not known, so they can support patients in their decision making,” Coyle says. The researchers are currently gathering data to determine if women are even talking to their physicians when deciding whether or not to eat their placentas.

“[For] women who are very conscientious about what they put in their body during pregnancy and nursing and who maybe would avoid raw fish or certain cheeses or whatever else,” Coyle says, “before making this decision just be aware that it’s still unknown what’s being consumed.”