The food supplies at the Convent-School of Saint-Cyr come close to offering the conditions of a laboratory experiment for the analysis of alimentary practices and norms of consumption. The data provides an historical take on our current preoccupations with the possibilities of modifying food habits by way of prices or by the dissemination of information. Food prices do not explain the how and the why of the supplies at Saint-Cyr, whose aristocratic status compelled it to respect certain consumptions. However, the managers were apparently informed about dietary recommendations which do much to account for the secular changes in this institution's food habits. Thus, historical research produces substantial knowledge on the determinants of food purchases; it also offers the opportunity to test the pertinence of a variety of methodologies used to explain (and act upon) the contemporary world.