Richard Smith , chair, Patients Know Best richardswsmith{at}yahoo.co.uk

From low fat to Atkins and beyond, diets that are based on poor nutrition science are a type of global, uncontrolled experiment that may lead to bad outcomes, concludes Richard Smith

Jean Mayer, one of the “greats” of nutrition science, said in 1965, in the colourful language that has characterised arguments over diet, that prescribing a diet restricted in carbohydrates to the public was “the equivalent of mass murder.”1 Having ploughed my way through five books on diet and some of the key studies to write this article, I’m left with the impression that the same accusation of “mass murder” could be directed at many players in the great diet game. In short, bold policies have been based on fragile science, and the long term results may be terrible.2 3 4 5 6

Attributing disease or mortality to diet is scientifically difficult. Associations are first made through observational studies, but recording exactly what people eat is hard. We eat very varied diets, and maybe over time our diets change. Then converting our diet into components of fat, carbohydrate, protein, and the like is unreliable. So to make a link between diet recorded over a short period of time and diseases and deaths encountered perhaps decades later is inevitably difficult.

Then intervention trials are unreliable. Unlike with a drug trial, where there will be one variable (taking or not taking the drug), trials of diet include more than one variable: for example, a diet of less fat probably means more carbohydrate so as to supply enough energy. Adherence is an important problem in drug trials but a much bigger problem in trials of diets, as people may find it very difficult to follow an unfamiliar diet. Also, the trials are usually short term and rarely include hard outcomes such …