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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 have two main concerns regarding the article entitled “Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study published in BMJ 2012;344:e4026 doi: 10.1136/bmj.e4026 (Published 26 June 2012).

1. The conclusions said that “low carbohydrate-high protein diets, used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, are associated with increased risk of cardiovascular disease”. The authors did not say that such observations are observed in women.

2. The study results revealed an association between low carbohydrate-high protein diet consumption and overall incidence of cardiovascular disease with incidence rate ratio estimates 1.04 (95% confidence interval 1.00 to 1.08), 1.04 (1.02 to 1.06), and 1.05 (1.02 to 1.08). Although such incidence rate ratio estimates are statistically significant since 95% confidence intervals (CI) do not overlap 1, the magnitudes of the strength of association are very minimal – the point estimates are closed to 1, the lower limits of 95% CI are very closed to 1 and the highest upper limit of 95% CI is only 1.08. These incidence rate ratio estimates from this cohort study should have no clinical importance and these associations should be due to a very large sample size. The authors should consider the appropriate number of the subjects to test the magnitude of the strength of association that has clinical importance (such as incidence rate ratio of 2) before conducting the study. The authors should include the aforementioned comments in terms of clinical importance of their findings in the article in order to avoid misunderstanding and misinterpretation of the readers and the media who do not have sufficient capacity to interpret the point estimate and 95% CI. Finally, the authors should say in the conclusions that the magnitude of the strength of the association they observed is minimal.

Competing interests: No competing interests

02 July 2012
Visanu Thamlikitkul
Physician
Siriraj Hospital
2 Prannok Road, Bangkok 10700, Thailand