Public Health Nutrition Editorial Highlight: ‘Source of bias in sugar-sweetened beverage research: a systematic review’ Authors: Ethan A Litman, Steven L Gortmaker, Cara B Ebbeling and David S Ludwig discuss their research below.

Numerous reviews of the scientific literature show that when a food company funds a nutrition study, the conclusions are much more likely to favor the sponsor’s financial interests than when the study is independently funded. This finding raises the possibility that research sponsored by the food industry might corrupt the scientific literature and undermine public health.

However, the associations between study sponsorship and outcomes cannot prove that industry-funding causes bias. Beyond financial relationships, other factors might in theory influence the design, conduct or interpretation of a study – such as when an investigator has a strongly held opinion, religious belief or even relevant personal practice (e.g., following a specific diet).

One special form of non-financial influence has been termed White Hat Bias to describe the possible tendency of some researchers to distort information “in the service of what may be perceived to be righteous ends” motivated by indignation toward industry. If White Hat Bias were prevalent, then perhaps the problem is with independent studies, not industry-funded studies.

These personal, subjective factors are increasingly being equated with objective financial conflicts of interest; and some journals now require that they be disclosed in published articles. Are all potential sources of bias basically alike? Or does considering them so normalize financial conflicts of interest and distract from a major, preventable causes of bias?

To address these questions, we used research on sugar-sweetened beverages (SSBs) as a test case. We focused on the 13-year period during which the field progressed from uncertainty to consensus regarding the adverse health effects of SSBs.

Among 133 relevant articles in the English literature, the proportion of industry-funded studies was 30% in 2001, decreasing to less than 5% by 2013. Overall, most independent studies (82%) reported adverse effects of SSBs, whereas very few industry-funded studies did so (7%). In addition, industry-funded studies were primarily cross-sectional observational analyses or reviews – designs that are either weak or especially susceptible to bias.

In light of current consensus, these findings indicate that industry-funded research systematically misperceived and underestimated the true adverse effects of SSBs on health during a critical time of evolving science. This potentially biased body of work was used by the SSB industry to undermine policy measures to limit consumption – such as taxes – suggesting a strategy by which producers of unhealthful products use flawed science to counter threats to profitability. (Note: our study does not suggest individual researchers receiving industry funding are intentionally complicit in this strategy).

In summary, we found that bias related to financial conflicts, dominated the literature involving SSBs during a critical period, to the potential detriment of scientific knowledge and public health. Given the now well-recognised impact of financial conflicts on study findings, we believe that recent policies to equate financial and non-financial conflicts are misguided.

The full article ‘Source of bias in sugar-sweetened beverage research: a systematic review’ published in Public Health Nutrition is available to download for free until 8th May 2018.