Richard Smith goes there at the BMJ. “Are some diets “mass murder”?”
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.” 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.
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 as cardiovascular events or deaths.
John Ioannidis, the scourge of poor biomedical science, has shown the great unreliability of most studies linking nutrition to disease and mortality, and perhaps we fail to recognise the complexity of relations between diet and disease when we pick out single components, whether it’s total fat, saturated fat, trans fats, sugar, or salt.
He goes on to praise and review Nina Teicholz’s The Big fat Surprise, which I also enjoyed. I will get to blogging about it one day. His piece is worth a read, too.