The objective of the study is to develop a simple, noninvasive test for evaluation of iron absorption as a tool to determine the cause of iron deficiency anemia. Healthy, premenopausal women with iron deficiency with or without anemia will be recruited for the study. Participants will, over the course of two months, ingest an iron solution three times; after each iron ingestion, participants will collect their stool and bring it to the study investigators for assessment of iron content.