Importance: Food industry sponsorship of nutrition research may bias research reports, systematic reviews, and dietary guidelines.
Objective: To determine whether food industry sponsorship is associated with effect sizes, statistical significance of results, and conclusions of nutrition studies with findings that are favorable to the sponsor and, secondarily, to determine whether nutrition studies differ in their methodological quality depending on whether they are industry sponsored.
Data sources: OVID MEDLINE, PubMed, Web of Science, and Scopus from inception until October 2015; the reference lists of included reports.
Study selection: Reports that evaluated primary research studies or reviews and that quantitatively compared food industry-sponsored studies with those that had no or other sources of sponsorship.
Data extraction: Two reviewers independently extracted data from each report and rated its quality using the ratings of the Oxford Centre for Evidence-Based Medicine, ranging from a highest quality rating of 1 to a lowest of 5.
Main outcomes and measures: Results (statistical significance and effect size) favorable to the sponsor and conclusions favorable to the sponsor. If data were appropriate for meta-analysis, we used an inverse variance DerSimonian-Laird random-effects model.
Results: Of 775 reports reviewed, 12, with quality ratings ranging from 1 to 4, met the inclusion criteria. Two reports, with data that could not be combined, assessed the association of food industry sponsorship and the statistical significance of research results; neither found an association. One report examined effect sizes and found that studies sponsored by the food industry reported significantly smaller harmful effects for the association of soft drink consumption with energy intake and body weight than those not sponsored by the food industry. Eight reports, including 340 studies, assessed the association of industry sponsorship with authors' conclusions. Although industry-sponsored studies were more likely to have favorable conclusions than non-industry-sponsored studies, the difference was not significant (risk ratio, 1.31 [95% CI, 0.99-1.72]). Five reports assessed methodological quality; none found an association with industry sponsorship.
Conclusions and relevance: Although industry-sponsored studies were more likely to have conclusions favorable to industry than non-industry-sponsored studies, the difference was not significant. There was also insufficient evidence to assess the quantitative effect of industry sponsorship on the results and quality of nutrition research. These findings suggest but do not establish that industry sponsorship of nutrition studies is associated with conclusions that favor the sponsors, and further investigation of differences in study results and quality is needed.