A serum resistin level reducing agent which comprises a disrupted product of a cell wall of Chlorella pyrenoidosa, can be used for reducing a serum resistin level, and is an agent for oral administration. A food or beverage composition for reducing a serum resistin level, which contains a disrupted product of a cell wall of Chlorella pyrenoidosa and can be used for reducing a serum resistin level. A method for reducing a serum resistin level by applying/administering a disrupted product of a cell wall of Chlorella pyrenoidosa through an oral route. Use of a disrupted product of a cell wall of Chlorella pyrenoidosa by the administration through an oral route for the purpose of reducing a serum resistin level.
