Corporation-financed research tends to be biased.

Scientific research on soft drinks, juices, and milk was four to eight times more likely to yield health results favorable to companies if it was sponsored by the food industry than research with no corporate ties, a study released last night found. The report suggests that nutrition research, like drug research, may be tainted by special-interest dollars.

Scientists from Children's Hospital Boston evaluated 111 beverage studies published between Jan. 1, 1999, and Dec. 31, 2003, and found that industry paid for some or all of a majority of the research, a finding that surprised even Dr. David Ludwig, a veteran nutrition researcher who presided over the Children's study. The Boston scientists, whose findings appear in the online journal PLoS Medicine, emphasized that they're not accusing individual researchers of scientific skullduggery, but also acknowledged that they don't have a definitive explanation for their results.

The ethics of scientific research has been a hot topic in classrooms and laboratories during the past few years, stoked by revelations that some studies of blockbuster painkillers ignored findings that would have made the medication look bad. And previous scientific reviews have shown that drug studies supported by pharmaceutical companies are more prone to side with industry than studies sponsored by government or universities.

This expanding body of research made Ludwig and his colleagues curious about the impact of corporate dollars on nutrition science.

"Conflicts of interest in pharmaceutical research could affect millions of people taking medicines," said Ludwig, director of the Optimal Weight for Life program at Children's. "Conflicts of interest in nutrition research could affect the health of everyone because we all eat."

The stakes of such research are higher than ever: As the American waistline balloons and patients deal with the complications of obesity, food companies are increasingly trumpeting the power of their products to stifle cancer, reverse heart disease, and shed pounds.

"I'm really glad they're publishing this," said Marion Nestle, a nutrition professor at New York University, because "food companies have only one purpose in funding research, and that's to use the results in marketing. If they can't use the results in marketing, then they're not going to fund it."

One of the studies included in the review examined whether heavy consumption of fruit juice made children shorter and fatter, as previous work had suggested. The researchers, who interviewed parents and weighed and measured children, didn't find such a link. The study was underwritten, in part, by Gerber Products Co., a leading maker of food for children.

An author of that study, retired University of Tennessee nutrition scientist Betty Ruth Carruth, said Gerber had approached her about doing a study of children and their eating habits after reviewing her earlier work.

"Yes, they funded it but they never, ever indicated to us that we had to do it one way or another," said Carruth, whose study was published in 1999 in the prestigious journal Pediatrics. "You establish going in that what data you get, that's what you report."

The Children's team limited their review to beverages -- in part, because drinks are highly profitable and because they're aggressively marketed to children.

The researchers hunted for studies appearing in scientific journals and then evaluated the studies' conclusions, rating them as favorable, neutral, or unfavorable to the beverage industry. The authors also examined the research papers to see whether they indicated who paid for the studies and classified them as being backed fully by industry dollars, partially supported by industry, or underwritten by entities outside the beverage industry.

Their finding: Industry paid in full for 22 percent of the studies, and partially for 32 percent more. And when looking only at studies that reached a favorable or unfavorable conclusion, research funded exclusively with industry money was as much as eight times more likely to result in findings positive for companies and their trade associations than studies with no industry money.

In one especially striking discovery, the Children's researchers looked specifically at those studies that directly intervened in participants' health by, say, providing a beverage to drink and then measuring participants' health. None of the industry-funded studies in that class produced unfavorable results, while 37 percent of those without industry sponsorship generated negative findings.

An executive with a leading dairy industry group said in an interview that his association only supports researchers with an impeccable track record of scientific integrity. When the National Dairy Council underwrites research, it aims for studies that will stress the benefits of dairy products, said Greg Miller, the council's executive vice president for science and innovation.

"We're not sticking our head in the sand and ignoring issues we need to be aware of," Miller said. "We want to be truthful. But the majority of studies are related to the role and the benefit of dairy products in a healthy diet."

In a given year, Miller said, the council provides anywhere from "a couple of million dollars" to as much as $9 million to support research. The council, he said, never asks researchers to manipulate data, but asks them to report back regularly about what they're finding and may ask them to consider additional factors in their studies. Miller said researchers funded by the council must promise to publish their results in journals that are reviewed by peer scientists.

The Dairy Council as well as the American Beverage Association, another industry confederation, lambasted the Children's report yesterday, saying it failed to assess the quality of each study.

"This is yet another attack on industry by activists who demonstrate their own biases in their review by looking only at the funding source and not judging the research on its merits," Susan K. Neely, president of the beverage association, said in a statement.

Ludwig said the researchers, whose study was funded by the Charles H. Hood Foundation and Children's Hospital, did not set out to assess the quality of individual studies but instead, to look for trends in funding and research outcomes.

The apparent link between funding sources and research outcomes could reflect everything from unconscious bias on the part of researchers to strategic decisions by food companies to sponsor only research likely to produce favorable results, nutrition specialists said.

Dr. JoAnn Manson, who has studied the deleterious health effects of sugar-laden soft drinks, said the Children's study offers a cautionary lesson for consumers.

"It suggests that it is very important when the public is hearing about a research study that they do understand who sponsored the study, the strength of the evidence, and whether the study findings are open to interpretation," said Manson, chief of preventive medicine at Brigham and Women's Hospital .