In nutrition research, strong economic interests exist, and concerns about biases have been raised. A frequent implication is that food and beverage industry scientists or industry-funded scientists act in a fashion that leads to downwardly biased estimates of the causal adverse health effects of their products. Vartanian et al13
reported that among observational studies of the association between NSB consumption and obesity, the estimated magnitude of an adverse association was statistically significantly larger among studies not funded by industry than among studies funded by industry, a concerning finding that merits further investigation. Conceivably, there could be opposite and competing publication biases such that industry researchers may be disinclined to publish significant results supporting a strong association between NSB consumption and obesity, and nonindustry scientists may be disinclined to publish results with non–statistically significant associations—a conjecture worthy of testing.
Furthermore, funders with a vested interest in the outcome of a study may weigh the probabilities of various outcomes before selecting an investigator and study design to fund. Competent, ethical investigators who approach questions from different perspectives and with varying methods (eg, short- vs longer-term trials, different study populations) may differentially attract industry funding, hence yielding valid outcomes, but may be more inclined to support one conclusion than another. Researchers of scientifically meritorious work that happens to support a funder's interests may also be more inclined to seek funding from the sponsor than those generating contrary findings. Collectively, these observations and hypotheses suggest at least 2 competing sets of factors at play—one that may lead industry-funded studies to show weaker associations of NSBs with obesity and another that leads non–industry-funded studies to provide upwardly biased estimates of this association as a result of publication bias.
Bias also may have entered discourse via secondary representations of results in the news media, or other subsequent peer-reviewed publications. For example, the report by Ebbeling et al8
describing an NSB reduction RCT stated that “change in body mass index (BMI) was the primary end point. . . . The net difference, 0.14 ± 0.21 kg/m2
, was not significant overall.” The authors then reported a subgroup finding: “Among the subjects in the upper baseline-BMI tertile, BMI change differed significantly between the intervention . . . and control . . . groups.”8
Contrast this modest finding in a sample subset and the circumspect presentation in the original article with the presentation of the findings in some news reports. For instance, a New York Times
article stated that “the teenagers who had been the most overweight had significant reductions in their body mass indexes at the end of the 25 weeks”14
and made no mention that the primary analysis in the total sample showed no significant effect. Likewise, a BBC news report indicated that “researchers found that the heavier the teenager had been initially, the stronger the effect on body weight,” again failing to mention the nonsignificant result overall.15
Similarly, some articles in the peer-reviewed literature10,11
described the study by Ebbeling et al as showing that NSB reduction reduces weight, obesity, or adiposity without explicitly stating that the results were not significant in the primary analysis of the total sample. Such statements have the potential to mislead readers who rely on secondary sources.
A third way the literature may have been distorted is by authors of review articles including some studies inappropriately and not including others that should be reviewed. For example, some past reviews13
have included a study of short-term (24-hour) weight changes that used weight as an index of hydration status and was never intended nor is adequate to assess the effects of habitual NSB consumption on adiposity. Thus, multiple factors, by no means limited to those with industry funding, seem to be leading to distortion of the research record on this controversial topic.