PURPOSE: A functional food containing a lipase-inhibiting agent such as dioscin or a dioscin derivative obtained from an extract of yam(Dioscorea batatas) or Dioscorea nipponica as an effective ingredient is provided. It is effective in improving or preventing disease selected from the group consisting of hyperlipidemia, arteriosclerosis and obesity. CONSTITUTION: The functional food contains dioscin represented by the formula(1) or a dioscin derivative selected form the group consisting of diosgenin, gracillin, prosaponin A and prosaponin C and is useful a food product for preventing obesity. The dioscin and dioscin derivative are obtained by extracting Dioscorea batatas., Dioscorea japonica, Dioscorea bulbifera, Dioscorea nipponica, Dioscorea tokoro, Dioscorea tenuipes, Dioscorea septemloba, Dioscorea quinqueloba or the like. The effective amount of dioscin is 50 to 500mg/kg, preferably 100 to 200mg/kg.