World epidemiology of non-celiac gluten sensitivity

While the term "gluten" has become commonplace, the disorders associated with gluten still remain poorly understood. Non-celiac gluten sensitivity (NCGS), the most recently recognized of the gluten-related disorders, is arguably the most unknown. While celiac disease and wheat allergy have diagnostic algorithm, NCGS remains a diagnosis of exclusion. With no evidence-based objective diagnostic criteria or serological tests, it is difficult to diagnose and even more difficult to study epidemiologically. Studies often use varied definitions of NCGS and are difficult to compare or validate. Further complicating diagnosis, NCGS has variable and wide-ranging symptoms which overlap with a number of other diseases and changes to diet are inherently difficult to study. In fact, some have argued that NCGS does not exist as a distinct entity or that it may not be caused by the gluten portion of foods. In this review, we outline the current knowledge, hypotheses, and debates surrounding the epidemiology of NCGS in the context of the spectrum of gluten-related disorders.