The classification of coumestrol as a phytoestrogen was based on its isolation by Bickoff et al. (1957) from alfalfa, ladino clover, and strawberry clover , all belonging to the Fabaceae family (Trifolium r epens L., Medicago sativa L., and T rifolium fragiferum L., respectively) (Melo et al., 2010). While legumes are primarily where coumestrol is found in diets, traces of it can also be spotted in vegetables such as Brussels sprouts and spinach. Clover and soybean sprouts are noted to have the richest content of coumestrol among all sources. Coumestans have a structure similar to that of isoflavones but with a five-membered ring instead of a six-membered ring (Tu et al., 2021). The backbone structure of coumestans consists of a benzopyran ring system fused to a benzene ring. The benzopyran ring system contains a six-membered oxygen-containing ring (known as a pyran ring) fused to a benzene ring. In coumestans, the benzopyran ring system is further substituted with various functional groups, such as hydroxyl (–OH), methyl (–CH3), or methoxy (–OCH3) groups, which can affect their biological activity (Figure 15.5). For example, the presence of hydroxyl groups on the coumestan backbone allows them to bind to ERs in the body and exhibit estrogenic activity (Jameera Begam et al., 2017).