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Comment & Response
March 19, 2020

Association of Dietary Fiber and Yogurt Consumption With Lung Cancer Risk

Author Affiliations
  • 1State Key Laboratory of Quality Research in Chinese Medicine, Faculty of Chinese Medicine, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Macau, China
JAMA Oncol. Published online March 19, 2020. doi:10.1001/jamaoncol.2020.0261

To the Editor We read with great interest a recent article by Yang et al.1 This pooled analysis investigated the associations of dietary fiber and yogurt intakes with lung cancer risk. The authors reported that dietary fiber and yogurt intakes were associated with reduced risk of lung cancer. Considering the associations between them remain unclear, this evidence-based research may help to guide practice. However, several issues might have compromised the strength of the evidence of this analysis.

First, the greatest concern is the interpretation of the meta-analysis results of the main outcome. The pooled data showed that the associations of dietary fiber and yogurt intakes with lung cancer risk were not statistically significant (P = .059 and P = .055, respectively) (eFigures 1 and 2 in the Supplement),1 the authors stated that both fiber and yogurt intakes were inversely associated with lung cancer risk, but they omitted more important information (ie, the overall effects were not significantly significant). Although multiple subgroup analyses were performed to assess the variations in the effects, in situations where no overall effects of treatments were observed, subgroup analyses were particularly unreliable, and the subgroup effects might be misleading and spurious. It was highly unlikely to accept the claims based on subgroup analyses or draw confirmatory conclusions from any significant subgroup findings.2,3

Second, the authors compared the associations of higher dietary fiber and yogurt intake vs lower intake with lung cancer risk, but the approach might be problematic. For example, the authors reported that individuals with the highest quintile of fiber intake showed a 17% lower risk than those with the lowest quintile, but it was still impossible to conclude whether fiber intake was significantly associated with the risk of lung cancer. It might be better to directly evaluate the associations of different amounts of fiber and yogurt intake with lung cancer risk.

Third, the inclusion and exclusion criteria for study selection were not described, which might result in uncertainty about the study selection. Only 10 prospective cohort studies from a lung cancer pooling project were included, and some other eligible trials were not included.4 The selective inclusion of trials might have introduced publication bias and undermined the validity of the results.

Lastly, the quality of the included trials and the evidence strength of the findings were not assessed in this study, thus failing to provide a guide for readers to appropriately interpret the results.5 Additionally, the references and individual cancer data of the included studies were not provided, which might somewhat compromise the trustworthiness and reproducibility of this study.

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Article Information

Corresponding Author: Qibiao Wu, MD, PhD, State Key Laboratory of Quality Research in Chinese Medicine, Faculty of Chinese Medicine, Macau Institute for Applied Research in Medicine and Health, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau 999078, China (qbwu@must.edu.mo).

Published Online: March 19, 2020. doi:10.1001/jamaoncol.2020.0261

Conflict of Interest Disclosures: Dr Wu reported receiving grants from the Science and Technology Development Fund, Macau SAR. No other disclosures were reported.

Funding/Support: This work was funded by the Science and Technology Development Fund, Macau SAR (File No. 130/2017/A3, 0099/2018/A3, 0096/2018/A3).

Role of the Funder/Sponsor: The Science and Technology Development Fund had roles in the design and conduct of the work but had no role in preparation, review, or approval of the manuscript and decision to submit the manuscript for publication.

Additional Information: Drs Wu and Leung contributed equally to this work.

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
2.
Tanniou  J, Smid  SC, van der Tweel  I, Teerenstra  S, Roes  KCB.  Level of evidence for promising subgroup findings: the case of trends and multiple subgroups.  Stat Med. 2019;38(14):2561-2572. doi:10.1002/sim.8133PubMedGoogle ScholarCrossref
3.
Sun  X, Ioannidis  JP, Agoritsas  T, Alba  AC, Guyatt  G.  How to use a subgroup analysis: users’ guide to the medical literature.  JAMA. 2014;311(4):405-411. doi:10.1001/jama.2013.285063PubMedGoogle ScholarCrossref
4.
Vieira  AR, Abar  L, Vingeliene  S,  et al.  Fruits, vegetables and lung cancer risk: a systematic review and meta-analysis.  Ann Oncol. 2016;27(1):81-96. doi:10.1093/annonc/mdv381PubMedGoogle ScholarCrossref
5.
Guyatt  G, Oxman  AD, Sultan  S,  et al.  GRADE guidelines: 11. making an overall rating of confidence in effect estimates for a single outcome and for all outcomes.  J Clin Epidemiol. 2013;66(2):151-157. doi:10.1016/j.jclinepi.2012.01.006PubMedGoogle ScholarCrossref
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