Soy formula feeding during infancy associated with severe menstrual pain in adulthood. New research suggests that infant girls fed soy formula are more likely to develop severe menstrual pain as young adults. The finding adds to the growing body of literature that suggests exposure to soy formula during early life may have detrimental effects on the reproductive system. Source 9t.
If these findings are true then what I gather is you shouldn't be trying to make humans vegetarians at birth. Breast milk comes from breasts for a reason. It's obviously not something that was meant to be produced synthetically. Sometimes the best solution is the most basic and simple solution that exists. In this case it's the most ancient solution that will forever exist.