The liver may play the largest role in metabolizing estrogen, and apparently it is dependent on protein to do so:
This suggests that in order to try to support the body's own ability to keep a balance between estrogen and progesterone, it would be wise to optimize two things: protein intake and liver function. Keep in mind that the liver may not need to be any where near a disease state in order to have less than optimal metabolic function. Protein needs vary widely depending on age, lifestyle, and whether there is any kind of disease process occurring. The typical need for protein in healthy adults is probably a minimum of 60-80 grams per day.