It depends on what the intention is for the use of soy. If it is to reduce post-menopausal symptoms, many studies have shown inconclusive evidence that it helps reduce them (http://www.ncbi.nlm.nih.gov/pubmed/15458907). However, if it is simply to increase dietary protein, there may be a need for it. If a woman over 40 has a difficult time intaking enough protein (which is generally around 5-7 ounces or 46 grams per day depending on activity level), then she would be justified in taking a supplement. However, if she can attain it through regular foods (which I highly recommend) such as meat, nuts and beans, then she should not need a protein supplement.