Dear Sir:
We read with interest 3 recent meta-analyses of nut consumption and risk of cardiovascular disease, type 2 diabetes, and all-cause mortality (1–3). Findings from all 3 meta-analyses suggested that higher intake of nuts decreased the risk of coronary artery disease, whereas it was not associated with risk of stroke. However, there were inconsistent conclusions on the association between nut consumption and risk of type 2 diabetes. The 2 meta-analyses by Zhou et al (1) and Luo et al (2) showed no association between nut consumption and risk of type 2 diabetes, whereas the meta-analysis by Afshin et al (3) showed that nut consumption decreased the risk of type 2 diabetes. We checked the included studies by Afshin et al (3) and found some problems in their meta-analysis.
First, the meta-analysis by Afshin et al included one ineligible study (4) that examined the association of nuts and peas in combination with risk of type 2 diabetes but not the nuts-specific effect. Second, the meta-analysis omitted one important study (5) that reported a positive association between nut consumption and risk of type 2 diabetes (≥5 servings/wk compared with <1 serving/mo—RR: 1.51; 95% CI: 1.13, 2.04). Third, the meta-analysis extracted RRs and 95% CIs without adjustment for BMI according to Pan et al (6). In our opinion, this might be inappropriate because BMI is the main confounding factor influencing the association between nut intake and the risk of type 2 diabetes.
Given the problems in the meta-analysis by Afshin et al (3), it is not surprising that the authors found a significantly inverse association between nut intake and risk of type 2 diabetes but the other 2 similar meta-analyses (1, 2) reported no association. In particular, the meta-analysis by Luo et al (2) performed subgroup analyses with adjustment for BMI. In the model adjusted for BMI, there was no association, although an inverse association was found in the model without adjustment for BMI on the basis of only 2 studies. Given the findings above, limited evidence supports the inverse association between nut consumption and risk of type 2 diabetes.
Acknowledgments
None of the authors had a conflict of interest.
Footnotes
Note: Afshin et al chose not to submit a reply.
REFERENCES
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