The present invention relates to a novel method of obtaining a factor involved in appetite control and/or body weight control, as well as genes obtained by said method, polypeptides encoded by said genes, or novel polypeptides obtained from the information on polypeptides encoded by said genes as a means for treating, controlling or diagnosing diseases associated with eating disorders and/or body weight control. Also the present invention relates to substances that inhibit the effects of said genes or said polypeptides as a means for treating, controlling or diagnosing diseases associated with appetite control and/or body weight control. By using thiazolidine diones having a PPAR .gamma. agonist activity, genes and polypeptides involved in appetite regulation and/or body weight reduction can be obtained. NESFATIN or the like obtained by said method can be used as a means for treating, controlling or diagnosing diseases associated with eating disorders and/or body weight control.