The term functional foods is a modern one, but plants used interchangeably as foods and as medicines, or foods “good for your health” have been part of human heritage since prehistoric times. Defining functional foods in ethnobotanical terms helps to identify a cross-disciplinary, heuristic approach to this field of study, which addresses the issue of relevance of ethnobotanical and historical data for present-day concerns. The so-called ethnobotanical approach to bioprospecting has been said to be more efficient than the random one, in particular when used alongside a phylogenetic approach. This article critically reviews theoretical bases, strengths and weaknesses of the quantitative ethnobotanical method, and proposes its use for a cross-cultural comparison of plant remedies for gastrointestinal problems. These remedies are very common in traditional pharmacopoeias, and are prevalent and almost limited to a few taxa that share a very similar phytochemical make up. For these reasons we believe that applying the ethnobotanical filter to functional foods bypasses some of the problems of this method.