The review, published in the latest edition of PLOS ONE journal, analysed 31 studies into artificial sweeteners between 1978 and 2014. The studies considered both the potentially beneficial effects of artificial sweeteners, such as weight loss, as well as harmful effects like diabetes.
According to the paper “the objectives of this systematic review are to determine whether risk of bias, results, and conclusions of reviews of the effects of artificially sweetened beverage consumption on weight outcomes differ depending on 1) sources of review sponsorship and 2) authors’ financial conflicts of interest.”
When researchers assessed the relationship between review sponsorship and review results, artificial sweetener industry sponsored reviews were more likely to have favourable results (3/4) than non-industry sponsored reviews, including reviews with no funding disclosed (1/23).
In terms of the relationship between review sponsorship and review conclusions, artificial sweetener industry sponsored reviews were more likely to have favourable conclusions (4/4) than non-industry sponsored reviews, including reviews with no funding disclosed, (15/23).
“It’s alarming to see how much power the artificial sweetener industry has over the results of its funded research, with not only the data but also the conclusions of these studies emphasising artificial sweeteners’ positive effects while neglecting mention of any drawbacks,” said co-author Professor Lisa Bero, head of the Charles Perkins Centre’s bias node.
“The results of these studies are even more important than the conclusion, as the actual results are used in the development of dietary guidelines.”
To test the hypothesis that reviews performed by authors with a conflict of interest with the food industry are more likely to report favourable results, the research compared the nine reviews from authors that had no conflicts of interest with the food industry with 22 reviews performed by authors with disclosed or non-disclosed conflicts of interest.
“None of the nine reviews performed by authors without conflicts of interest reported favourable results; whereas four reviews with authors with conflicts of interest had favourable results,” they reported.
Reviews performed by authors with a conflict of interest with the food industry were also more likely to report unclear results (11/22) than reviews performed by authors without conflicts of interest (1/8).
Furthermore the review states 42% (13/31) of authors had conflicts of interest that were not disclosed in the article.
Professor Bero said transparency around an author’s conflicts of interest and research funding sources for this area of nutrition science is “sadly lagging behind other fields.”
“Our analysis shows that the claims made by artificial sweetener companies should be taken with a degree of scepticism, as many existing studies into artificial sweeteners seem to respond to sponsor demands to exaggerate positive results, even when they are conducted with standard methods.
“Ultimately it is consumers who lose out from this practice because our findings show that the results of reviews on the health benefits of artificial sweeteners cannot always be trusted. Measures to eliminate sponsor influence on nutrition research are desperately needed.”
The review also claims that reviews published in journals funded partially or in full by the food industry more often have conclusions that are favourable towards artificially sweetened beverages than reviews published in non-industry funded journals.
The researchers concluded: “Our systematic review shows that financial conflicts of interest introduced a bias at all levels of the research and publication process (author financial ties, review sponsorship and journal funding), affecting the outcomes of reviews and possibly undermining the quality and transparency of public health evaluations that are reliant on these reviews. The bias introduced by financial interests could not be ascribed to the overall risk of bias of the reviews and was not prevented by the peer review process.”
The PLOS ONE study is the first major review of the effects of funding bias in nutrition research from the Charles Perkins Centre’s Bias in Research project node, a research collaboration aimed at improving health policy by encouraging unbiased and evidence-based research.
The study, published the same week that the sugar industry came under fire for influencing the integrity of scientific research, was conducted in collaboration with researchers from the Johns Hopkins Bloomberg School of Public Health and the University of California San Francisco.