Faecal transplants (microbiota transfer) have shown to be promising therapies having a wide range of therapeutic applications. However, current safety considerations hamper further valorisation. As such, well designed faecal transplant analogues provide an interesting alternative to minimize possible safety aspects. However, to date little knowledge on how to rationally design such analogues exists. Here, we show by applying first order basic graph theory that such analogues dedicated to restoring a specific physiological functionality (a microbial guild) should consist of 5-6 species to maximize stability, efficiency, and minimize safety issues and production costs.