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Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study

BMJ 2012; 344 doi: https://doi.org/10.1136/bmj.e4026 (Published 26 June 2012) Cite this as: BMJ 2012;344:e4026

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

02 July 2012
Álvaro campillo-Soto
General Surgeon & Scientific Metodologist
University General Hospital "JM Morales Meseguer"
Marqués de los Vélez s/n Murcia. Spain. CP: 30008