Methods of treatment using Fzd8 extracellular domains (ECDs), Fzd8 ECD fusion molecules, and/or antibodies that bind Fzd8 are provided. Such methods include, but are not limited to, methods of treating obesity and obesity-related conditions. Fzd8 ECDs and Fzd8 ECD fusion molecules are also provided. Polypeptide and polynucleotide sequences, vectors, host cells, and compositions comprising or encoding such molecules are provided. Methods of making and using Fzd8 ECDs, Fzd8 ECD fusion molecules, and antibodies that bind Fzd8 are also provided.