Re: White rice consumption and risk of type 2 diabetes: meta-analysis and systematic review
In our meta-analysis on white rice consumption and diabetes risk,1 we included more than 13,000 newly-diagnosed type 2 diabetes patients identified from more than 350,000 participants in four studies. In epidemiological studies of such a large scale, monitoring all participants for blood glucose levels is simply infeasible. In addition, we want to further stress that the effects of inclusion of undiagnosed diabetes during follow-up are likely to be small and tend to bias the results toward the null. The self-reported diabetes diagnosis has been demonstrated to be accurate in the US and Japanese studies.2 3 In the Chinese study, high rice consumption was correlated with lower socioeconomic status,4 which may lead to under-diagnosis of diabetes, although such a bias is most likely to attenuate true associations.
We followed a standard and comprehensive protocol in searching relevant literature, and we did not apply any restriction on language. Identification of unpublished data is infeasible, if not impossible. The quality of such data is difficult to examine in that those data are not evaluated by peer-review.
Data quality assessment is critical to meta-analyses. We followed current guidelines and customized quality assessment criteria by putting much weight on the assessment of diet, which is fundamental to all nutritional epidemiological research.
The significant heterogeneity that Naqvi et al noted was due to ethnicity. We, therefore, reported pooled estimates for Asian and Western populations, respectively.
Lastly, Naqvi et al erroneously used cumulative incidence or risk to describe prevalence. Apparently, the participants included in these studies were not representative of general population in each country, let alone the whole world. Although this unrepresentativeness may limit generalizability, it does not necessarily affect the internal validity of the results.
1. Hu EA, Pan A, Malik V, Sun Q. White rice consumption and risk of type 2 diabetes: meta-analysis and systematic review. BMJ 2012;344:e1454.
2. Manson JE, Colditz GA, Stampfer MJ, Willett WC, Krolewski AS, Rosner B, et al. A prospective study of maturity-onset diabetes mellitus and risk of coronary heart disease and stroke in women. Arch Intern Med 1991;151(6):1141-7.
3. Nanri A, Mizoue T, Noda M, Takahashi Y, Kato M, Inoue M, et al. Rice intake and type 2 diabetes in Japanese men and women: the Japan Public Health Center-based Prospective Study. Am J Clin Nutr 2010;92(6):1468-77.
4. Villegas R, Liu S, Gao YT, Yang G, Li H, Zheng W, et al. Prospective study of dietary carbohydrates, glycemic index, glycemic load, and incidence of type 2 diabetes mellitus in middle-aged Chinese women. Arch Intern Med 2007;167(21):2310-6.
Competing interests: No competing interests