The results, published on-line in the journal Public Library of Science - Medicine, are based on a review of 206 review and research articles that focussed on studies using soft drinks, fruit juices, and milk with health-related outcomes.
"The main finding of this study is that scientific articles about commonly consumed beverages funded entirely by industry were approximately four to eight times more likely to be favourable to the financial interests of the sponsors than articles without industry-related funding," wrote lead author Lenard Lesser from the Children 's Hospital, Boston.
The researchers started with 538 articles, but rejected over half of these because they failed to meet specific inclusion criteria including stating health outcomes or disease markers, involving humans or human tissue, classifiable as an interventional or observational study or a scientific review, and explicitly state the beverages' effects on health measures.
"We chose beverages because they represent an area of nutrition that's very controversial, that's relevant to children, and involves a part of the food industry that is highly profitable and where research findings could have direct financial implications," said lead reviewer Dr. David Ludwig.
Of the 206 eligible articles, only 111 declared financial sponsorship - 22 per cent were funded entirely by industry, 47 per cent had no industry funding, and 32 per cent had mixed funding.
The reviewers report that all-industry funded interventional studies were 37 per cent less likely to have unfavourable conclusions than those with no industry funding, while among all types of studies, comparing all-industry versus no-industry funding, the odds ratio for having a favorable versus unfavorable conclusion was 4.37, increasing to 7.61 when beverage type, publication year and examination of authors' personal conflicts of interest were taken into account.
"We don't all take drugs, but we eat every day," said Ludwig. "If the science base is compromised by conflict of interest, that's a top-order threat to public health."
The review appears to undermine the integrity of both industry and their university-based collaborators, but both industry and some scientists have come forth to balance the argument.
Indeed, the American Beverage Association (ABA), which regularly sponsor scientific studies, has reacted strongly to the claims, and countered that the review itself was biased.
Susan Neely, president and chief executive officer of the ABA, said: "This is yet another attack on industry by activists who demonstrate their own biases in their review by looking at the funding source and not judging the research on its merits. The science is what matters - nothing else."
"By not disclosing the studies examined, it is entirely possible that articles were excluded simply because they did not prove the authors' point," she said. "In addition, a bias may be present by failing to disclose that one of the authors is actually on the editorial board of the publication."
The ABA said that when it funds studies, decisions about the design, statistical analysis, results or conclusions are left entirely to the researcher to ensure that no bias exists. The association also stated that it insists on full disclosure of funding and that studies are published in peer-review journals.
The reviewers state however, that measures were implemented to guard against bias, by analysing the studies independently. One investigator selected the articles for inclusion according to pre-established criteria. Another two investigators, said to have no knowledge of the financial sponsors, and who were not told the article's author, title or journal of publication, classified the articles' conclusions as "favourable," "neutral" or "unfavourable." A fourth investigator, said to have no knowledge of the conclusions, determined the funding source and classified articles as to whether a favourable finding would be beneficial, negative or neutral to its funder's financial interests.
In an accompanying perspective in the same journal, Martijn Katan from the Vrije Universiteit in Amsterdam said that the study was "carefully done, the number of articles was sufficiently large, the analyses were straightforward, and they agree with the outcomes of earlier, smaller studies."
"However, an association between funding and outcome does not by itself prove bias," he said.
Katan points out that when industry plans to fund a study, "they will naturally select a product with a potentially favourable nutritional profile."
Katan also pointed out however, that it was unlikely that industry would fund a study into potentially unfavourable effects.
"My personal experience makes me reluctant to support a blanket condemnation of industry-supported research, because collaboration with industry has allowed me to discover things that I could not have found otherwise," he said.
"But researchers dealing with industry may be subjected to pressure, and they need help to resist such pressure… The Lesser et al. study raises serious concerns that some food industries may distort the scientific record on diet and health. Such concerns affect nutrition science as a whole, if only because they threaten public confidence in nutrition research, and once that confidence is gone nutrition research becomes irrelevant," said Katan.
Nutrition Scientist, Claire Williamson from the British Nutrition Foundation, a scientific and educational charity, told NutraIngredients.com that the review was "interesting" but "concerning [in] that it suggests industry funding may be affecting the outcome of nutrition-related reserch."
Williamson said that this effect could be similar to the phenomenon of observer/interviewer bias in a controlled experiment, which is the reason why studies should always be blinded.
"As the authors point out, however, there have been few previous studies looking at sponsorship bias in nutrition research, therefore further studies would be useful to elucidate whether these findings are repeated," said Williamson.
"Independent funding should help to reduce this type of bias, however, sources of independent funding are limited, and industry funding is likely to continue to be necessary in order to be able to fund the many studies needed in the growing field of nutrition and health research," she said.
Source: Public Library of Science - Medicine Published on-line. Volume 4, Issue 1, e5 "Relationship between funding source and conclusion among nutrition-related scientific articles" Authors: L.I. Lesser, C.B. Ebbeling, M. Goozner, D. Wypij, D.S. Ludwig