Provided is a composition for promoting ketone body production that comprises a water insoluble polymer of a ²-hydroxy short-medium chain fatty acid such as homopolymer of ²-hydroxybutyric acid or a copolymer of ²-hydroxybutyric acid and ²-hydroxyvaleric acid. The composition is useful for the treatment or prevention of a disease or condition that can be treated by promoting ketone body production.