Can industry-sponsored studies of the health and safety of its own products really be believed?

That long-debated question is now being raised about studies financed by the beverage industry refuting claims that soda and other sugary drinks can contribute to type 2 diabetes and obesity.

An analysis published in the Annals of Internal Medicine shows that out of 60 studies of sugary drinks, 26 saw no link to health problems—and all were funded by groups tied to the beverage industry.

These groups included those with an interest in promoting sugary drinks or researchers who had financial ties to a company or group supporting sugar-filled drinks. 

Of the 34 studies that did find a connection between sugary-drink consumption and obesity or type 2 diabetes, only one of the studies was sponsored by the sugary-drink industry.

“Our findings support the notion that sugar-sweetened beverages do indeed cause diabetes and obesity,” says Dean Schillinger, M.D., the lead author of the study and a professor of medicine in residence at the University of California, San Francisco.

“Science is never 100 percent certain, but based on what we know now, I’d say we’ve moved away from controversy and much closer to fact,” says Schillinger, who is also chief of the division of general internal medicine at San Francisco General Hospital.

In a statement, The American Beverage Association said: "We have a right—and a responsibility—to engage in scientific research. The research we fund adheres to the highest standards of integrity for scientific inquiry based on recognized standards by prominent research institutions." 

Schillinger's study came out of research he did as a paid medical consultant for San Francisco, which is battling a lawsuit brought by The American Beverage Association and other groups to block a city ordinance requiring health warnings on billboards and ads for sugar-sweetened beverages.

Last May, a federal judge ruled that the law could go forward, but the industry groups are appealing and the case is yet to be decided.

“The industry has been hinging its argument against laws and other actions to curb sugary-drink consumption by saying that evidence linking these beverages to health problems is highly scientifically controversial,” says Schillinger. "Because of that, they have said we can’t make public policy to reduce consumption."

His study, he says, suggests that it's the companies with a financial interest in sugary drinks that are creating conflicting information.