Few well-defined, evidence-based nutritional recommendations for people with skin diseases have been published in the scientific literature and standard dermatological textbooks. Using a systematic review of acne vulgaris as an example, the aim of this study was to determine whether there are systematic studies on the topic and, if so, of what quality. Four evidence levels were defined: (A) double-blind randomized study; (B) randomized study with serious limitations/low number of cases; (C) case-control or cohort study; and (D) expert opinion/case report. PubMed and Cochrane searches were performed using combinations of the terms "diet", "nutrition", "meal" and "food" with "acne". Foodstuffs mentioned in relevant articles were subdivided by evidence level and recorded as having a beneficial (+), neutral (0) or adverse (-) effect. However, only a small proportion of studies met sufficiently high scientific standards that would enable therapeutic recommendations to be made in practice.