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Comment & Response
March 19, 2020

Association of Dietary Fiber and Yogurt Consumption With Lung Cancer Risk—Reply

Author Affiliations
  • 1Vanderbilt Epidemiology Center, Division of Epidemiology, Department of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, Tennessee
JAMA Oncol. Published online March 19, 2020. doi:10.1001/jamaoncol.2020.0270

In Reply We have carefully reviewed the letter from Wu and Leung regarding our recent JAMA Oncology article on fiber and yogurt consumption and lung cancer risk.1 We believe that there were misunderstandings and misinterpretations of the study design and results.

Their main concern about the study conclusion was related to P values we presented in the Supplement (P = .059 in eFigure 1 and P = .055 in eFigure 2).1 Wu and Leung considered these P values as evidence of statistical nonsignificance for overall findings. In fact, these P values represented significance of heterogeneity tests, indicating no statistically significant heterogeneities in lung cancer risk estimates associated with fiber and yogurt intakes across studies. The overall summary estimates for association (hazard ratios), presented in eFigures 1 and 2, were 0.83 (95% CI, 0.76-0.91) for fiber intake and 0.81 (95% CI, 0.76-0.87) for yogurt intake, which were statistically significant.1

Regarding their second critique, we presented detailed estimates for all categories of dietary fiber and yogurt intakes in Table 2 and eTable 3 of the Supplement.1P values for trend tests were also presented in those tables and were highly statistically significant. For a simple visual presentation of consistent study results, we chose to present only the results for the highest quintile compared with the lowest quintile from each study in eFigures 1 and 2, noting that these results were generated from analyses that included all study participants. In addition, we presented dose-response relationships of fiber intake and yogurt consumption with lung cancer risk in eFigure 3 in the Supplement.1

Wu and Leung also mistook the study, a consortium-based pooling project, for a literature-based meta-analysis. As described in the Methods,1 the study was based on an international consortium and included individual data of more than 1.4 million participants from 10 well-established population-based cohorts. We applied 2 parallel analyses—a pooled individual data analysis and a cohort-specific analysis followed by a meta-analysis. Our study is an original research project and not a systematic review. Therefore, the critique on publication bias does not apply, nor does the critique on the omission of clinical trials.

Finally, cancer outcomes of the study were ascertained by each individual cohort with proven protocols, and details have been previously reported in the citations provided in the article.1 We applied a rigid quality control in our statistical analysis, and all analytic programs were checked by an independent researcher. We were restricted by cohort institutional review boards from sharing cohort member information.

We appreciate Wu and Leung’s interest in the research findings. Nonetheless, we believe that their critiques were unfounded and resulted from misunderstandings of the study design and misinterpretations of the statistics.

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Article Information

Corresponding Author: Xiao-Ou Shu, MD, PhD, Vanderbilt Epidemiology Center, Division of Epidemiology, Department of Medicine, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, 2525 W End Ave, Ste 600, Nashville, TN 37203-1738 (xiao-ou.shu@vumc.org).

Published Online: March 19, 2020. doi:10.1001/jamaoncol.2020.0270

Conflict of Interest Disclosures: None reported.

References
1.
Yang  JJ, Yu  D, Xiang  YB,  et al.  Association of dietary fiber and yogurt consumption with lung cancer risk: a pooled analysis  [published online October 24, 2019].  JAMA Oncol. doi:10.1001/jamaoncol.2019.4107PubMedGoogle Scholar
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