From the Impossible Burger to “Meatless Mondays,” going meat-free is certainly in vogue. But a person’s genetic makeup plays a role in determining whether they can stick to a strict vegetarian diet, according to a new Northwestern Medicine study.

The findings open the door to further studies that could have important implications regarding dietary recommendations and the production of meat substitutes.

“Are all humans capable of subsisting long term on a strict vegetarian diet? This is a question that has not been seriously studied,”said corresponding study author Dr. Nabeel Yaseen, professor emeritus of pathology at Northwestern University Feinberg School of Medicine.

A large proportion (about 48 to 64%) of self-identified “vegetarians” report eating fish, poultry and/or red meat, which Yaseen said suggests environmental or biological constraints override the desire to adhere to a vegetarian diet.

“It seems there are more people who would like to be vegetarian than actually are, and we think it’s because there is something hard-wired here that people may be missing.”