Apropos: “Gut Microbiota Differences in Children From Distinct Socioeconomic Levels Living in the Same Urban Area in Brazil”

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To the Editor: The study authored by Mello et al (1) introduces a novel insight by comparing the human gut microbial composition in children living in the same geographic area, stratified by socioeconomic status. The authors, however, make conclusions that are not supported by the author's study results or methods. The authors failed to properly explain how the community leaders and researchers defined the classification requirements for a “slum” within the study area. Mello et al discussed the location of the perceived “slum” and presented example pictures of the area; however, detailed criteria to what constituted as a “slum” are missing and lead readers to believe slums were identified subjectively. A subjective approach to identifying “slums” will lead to selection bias drastically skewing the study results.
In addition, the authors do not discuss the study's significant limitations, including the lack of a food diary collection, a crucial measure for establishing a baseline dietary picture for each study participant. Even though the authors discussed the differential dietary categories among the groups, it is curious that the authors decided not to do any kind of dietary data collection/analysis for this study group.
Finally, it is crucial, even in studies not evaluating microbiota composition dynamics over time, to collect multiple samples to effectively judge the accuracy and consistency of the sample collection process. These practices will reduce error and increase confidence in eventual study conclusions.
Future human gut microbiota–related studies must take greater care and deference in sound study design to avoid these problems in the future.
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