Relationship between Research Outcomes and Risk of Bias, Study Sponsorship, and Author Financial Conflicts of Interest in Reviews of the Effects of Artificially Sweetened Beverages on Weight Outcomes: A Systematic Review of Reviews

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Author(s): Mandrioli D, Kearns CE, Bero LA
Publication name: PLoS ONE 11(9): e0162198. doi:10.1371/journal.pone.0162198
Publication year: 2016


BACKGROUND: Artificially sweetened beverage consumption has steadily increased in the last 40 years. Several reviews examining the effects of artificially sweetened beverages on weight outcomes have discrepancies in their results and conclusions.
OBJECTIVES: To determine whether risk of bias, results, and conclusions of reviews of effects of artificially sweetened beverage consumption on weight outcomes differ depending on review sponsorship and authors’ financial conflicts of interest.
METHODS: We performed a systematic review of reviews of the effects of artificially sweetened beverages on weight. Two assessors independently screened articles for inclusion, extracted data, and assessed risks of bias. We compared risk of bias, results and conclusions of reviews by different industry sponsors, authors’ financial conflict of interest and journal sponsor. We also report the concordance between review results and conclusions.
RESULTS: Artificial sweetener industry sponsored reviews were more likely to have favorable results (3/4) than non-industry sponsored reviews (1/23), RR: 17.25 (95% CI: 2.34 to 127.29), as well as favorable conclusions (4/4 vs. 15/23), RR: 1.52 (95% CI: 1.14 to 2.06). All reviews funded by competitor industries reported unfavorable conclusions (4/4). In 42% of the reviews (13/31), authors’ financial conflicts of interest were not disclosed. Reviews performed by authors that had a financial conflict of interest with the food industry (disclosed in the article or not) were more likely to have favorable conclusions (18/22) than reviews performed by authors without conflicts of interest (4/9), RR: 7.36 (95% CI: 1.15 to 47.22). Risk of bias was similar and high in most of the reviews.
CONCLUSIONS: Review sponsorship and authors’ financial conflicts of interest introduced bias affecting the outcomes of reviews of artificially sweetened beverage effects on weight that could not be explained by other sources of bias.


The Mandrioli et al. review paper raises serious concerns about its objectivity, since the conclusions, namely sponsorship affects results and conclusions of a review, are based on a subjective evaluation of a few reviews that were classified as “favorable” or “unfavorable” on the basis of a questionable algorithm. However, the authors classified as “favourable” reviews that reported no association or inconclusive/ negative results and, therefore, the main conclusion of the paper is highly questionable.

Specifically, the findings in Mandrioli ei al are based only on 4 reviews that were classified as “favourable” (out of a total of 31), from which one is a commentary and not a review and should not be included in the analysis in the first place, while from the remaining three reviews, one is mistakenly classified as positive, whereas it is obviously negative. As a result, only two reviews meet the criteria of the study, which is an extremely small number to draw any conclusions. Furthermore, most of the relative risks (RRs), as estimated in the statistical analysis, were based on extremely low numbers and hence are largely unstable. The authors fail to recognise the above biases and limitations in their systematic review, which raise serious concerns about the quality of the study and the accuracy of its outcomes. For more information please read the ISA comments by clicking here.

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