An interesting piece of research demonstrating a correlation between raw vegan diet and low bodyweight and amenorrhea in a sample of women… you can read it here.
From a Chinese medicine dietary therapy point of view, the raw food diet has taxed these women’s digestive system to the point at which the production of blood is slowed or even stopped. In Chinese medicine, the production of blood begins in the Spleen-Stomach digestive system. If blood is not produced in ample quantities, women will have amenorrhea because there is insufficient blood to menstruate. I would wager that these women would also be found to be anemic by blood test.
I would also wager that this population would have fewer women with amenorrhea if they switched from a raw vegan diet to a vegan diet including cooked food. For some, the consumption of cooked food would help enough to reverse the amenorrhea.