Re: Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study
I've read the article with high expectations but, after reading it, I'm very sad, because I don´t understand why the BMJ, one of the best medical journals in the world, has published an article so biased. If we look over it we can see the following biases:
1º.- Methodological bias: The authors only send a questionaire in 1992 and 15 years later without: 1) New questionaires; 2) Patients´ follow-up; 3) Information about the patients' habits. They jump to conclusions based on biased and misleading arguments.
2º.- Selection bias: At least 1 out of 2 patients rejected being included in this study.
3º.- Measurement bias: Authors know nothing about the life habits of patients.
4º.- Follow-up bias: Only one questionnaire is NOT appropiate follow-up.
5º.- Expectation bias: The absence of masking or blinding may err in measuring data toward the expected outcome.
6º.- Insensitive measure bias: The measurement tool used in this study is not sensitive enough to detect important differences in the variable of interest.
7º.- Compliance bias: Nobody knows if there is a adherence to the reported diet habits.
8º.- Misclassification bias: It's impossible to know if patients are classified correctly (Low carb vs High carb).
9º.- Confounding bias: In this study no more than 51% of potential patients were included.
10º.- Non-response bias (49% of potential patients!): Limits generalizability, not validity.
So far as the scientific methodology is concerned, the conclusion of this article should be the following:
“This medical paper has both a very low quality and a lot of major biases, therefore it shouldn´t be published because its flaws not only have a confounding effect in nutrition science but can generate emotional shock in people under these kind of diets"
According to Stephen Lock (ex-editor of BMJ): "Medical journals will soon be wrapping up next week´s fish and chips".
Competing interests: No competing interests