Garcia-Larsen et al. wrote a meta-analysis on the association between dietary patterns derived from principal component analysis (PCA) and the risk of colorectal cancer, as published in the March issue of this journal .
We have some concerns about the paper that we hope the authors can address. In any meta-analysis it is important to consider whether the exposure of interest and the outcome of interest are comparable enough to warrant combining and meta-analyzing the findings. As the authors acknowledge in their paper, the exposure of interest (‘Western’ or ‘prudent’ dietary patterns) varies considerably between studies, likely contributing to heterogeneity in their findings. More importantly however, the authors retrieved papers with a diversity of outcomes in their review: some papers had colorectal cancer incidence as outcome, others colorectal adenomas, colorectal cancer incidence combined with overall mortality, disease-free survival or reoccurrence of colorectal cancer. In the presented meta-analyses and forest plots, the authors decided to combine all outcomes and to present results as if there was only one outcome. We would argue that colorectal cancer incidence and disease-free survival or reoccurrence of colorectal cancer are very distinct outcomes, and should not be combined in one meta-analysis; neither should colorectal adenomas or mortality.
Garcia-Larsen V, Morton V, Norat T, Moreira A, Potts JF, Reeves T, et al. Dietary patterns derived from principal component analysis (PCA) and risk of colorectal cancer: a systematic review and meta-analysis. Eur J Clin Nutr. 2019;73:366–86.
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Winkels, R.M., van Zutphen, M. Multiple outcomes in a meta-analysis of dietary patterns and colorectal cancer. Eur J Clin Nutr 74, 208 (2020). https://doi.org/10.1038/s41430-019-0487-9