WASHINGTON—One study shows that milk can help people lose weight. Another shows that tomato juice might prevent cancer and a third shows benefits to fizzy sodas.
But consumers should take those studies with a grain of salt, researchers reported Feb. 8.
If a study was industry-funded, it was far more likely to have a positive finding than if it was paid for by the government or an independent group, the researchers found.
"We are not singling out any industry or any particular study," said lead researcher Dr. David Ludwig of Children's Hospital Boston and Harvard University.
"Our first look shows evidence strongly suggestive of bias," Ludwig said in a telephone interview.
The study, published by the Public Library of Science online journal PLoS Medicine, echoes other findings that show industry-funded research on drugs is more likely to be favorable to the drugs than independent research.
Ludwig's team reviewed 111 studies on soft drinks, juice, and milk that were published between 1999 and 2003.
"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," Ludwig said.
Studies funded entirely by industry were four times to eight times more likely to be favorable to the financial interests of the sponsors than those paid for by other groups, the researchers found.
Of the 22 studies clearly identified as funded by companies or industry groups, just three, or 13.6 percent, had findings that were unfavorable to the beverage studied.
More than 38 percent of the independently funded studies were negative, the researchers found.
This "raises serious concerns that some food industries may distort the scientific record on diet and health," Martijn Katan, professor of nutrition at Vrije Universiteit in Amsterdam, wrote in a commentary in the same journal.
Ludwig said the studies could be set up differently if they are funded by industry. Or it could be that sponsors choose not to publish studies that turn out unfavorable to their product, he said.
Researchers funded by industry may do rigorous work, but may choose to ask certain questions more likely to produce a result favorable to the product, Ludwig said. "I don't blame researchers for this problem. I think that most are highly ethical and dedicated to science," Ludwig said.
He said the problem is that the government does not spend much money studying nutrition.
"Industry money becomes difficult to resist," he said. "Imagine ... you are facing the choice of accepting industry money or closing up shop."
Ludwig's study was paid for by his hospital and by the Charles H. Hood Foundation, a childhood health philanthropy.