Our lab studies how estrogens influence metabolism and anxiety in female mice. Estrogens have profound effects on weight gain and anxiety in women and female rodents. For example, post-menopausal women have decreased levels of estrogens leading to increased anxiety and weight gain, which increases their risk of obesity, diabetes, heart disease and cancer. Estrogens have similar effects on anxiety and metabolism in female mice. We and others have shown that ovariectomized mice fed a high-fat diet become obese, while mice treated with estrogens remain lean (Bless et al., 2014). We have extended these studies on energy homeostasis to include how estrogens influence the gut microbiome, which is a collection of microorganisms (bacteria, viruses, archaea, protozoa and fungi), their genomes and the factors they produce in the gut.  The gut microbiome has been implicated in a variety of disorders and diseases, including obesity, diabetes, depression and anxiety (Tetel et al., 2018). Using genetically altered mice that lack the hormone leptin (ob/ob) and are obese (Acharya et al., 2019), we found that obesity and estrogens were associated with reduced diversity of the gut microbial community. Understanding the role of estrogens in regulating gut microbiota will provide important insights into hormone-dependent disorders of anxiety and metabolism in women.