Health information leaflets are often written at too high a level to be understood by large numbers of patients. There is a direct link between low literacy and poor health; difficulties comprehending written health material may explain part of this link. Guidelines on how to simplify written health information do exist. However, it has not been conclusively demonstrated that lowering readability can increase patient satisfaction and understanding. The present study hoped to show this by examining the differences between two versions of the same informative content differing only in readability level (a short section from a diabetes educational leaflet). Knowledge increase, ease of reading and personal preference were measured via questionnaires in two separate studies, examining two different populations: in Study One, a university-educated sample (with high reading skills), and in Study Two, a sample of literacy learners (with lower reading skills). In Study One, participants reading the lower-readability section gained more knowledge about diabetes, and participants indicated a strong preference towards the lower-readability version. Study Two’s results were more mixed: although participants reading the rewrite gained slightly more knowledge, the amount participants learned about diabetes was unlikely to be clinically significant. Additionally, no clear preference for the rewrite was shown. Based on Study One’s results, it is concluded that health information should be written as simply as possible (while preserving all important informative content). People with good reading skills can understand easier versions of health material, but people at lower educational levels will not benefit from more difficult materials. Study Two suggests that written health materials may not be suitable for populations with low reading skills; however, flaws in its methodology and sample mean this remains speculative. Future research must address these limitations.