By now, you've very likely heard the case for limiting sugar.

Over the past two years the World Health Organization and the U.S. Dietary Guidelines have begun urging us to consume no more than 10 percent of our daily calories from added sugar. Drinking more than one sugar-sweetened soda a day can put you over that limit.

But a new industry-funded study published in a prominent medical journal questions the evidence used to generate the specific recommendations to limit sugar in our diets.

"Overall, I would say the guidelines are not trustworthy," says study author Bradley Johnston, a clinical epidemiologist at the Hospital for Sick Children in Toronto who also teaches biostatistics.

Johnston reviewed the studies and methodology used to generate the guidelines. He concludes that while it's wise for people to limit sugar consumption, there's still a question about how much to limit.

"Sugar should certainly be limited in the diets of children and adults, no question," he says. But he argues there's not convincing evidence to support cutting consumption to 10 percent, or 5 percent — or any specific threshold.

"There's a lot of uncertainty about the thresholds that appear in guidelines," Johnston says. "What's happening is that guideline panelists are making strong recommendations based on low-quality evidence." (The paper reviewed nine sugar-intake guidelines from around the globe, included the WHO guideline and the Dietary Guidelines for Americans, which were updated this year.)

The paper, which appears Monday in the Annals of Internal Medicine, has raised the ire of public health experts. "We should reject these findings," says Dean Schillinger, a physician at the University of California, San Francisco and advocate for diabetes-prevention efforts.

Schillinger has penned an editorial, published alongside the study, that's titled, "Guidelines To Limit Added Sugar Intake: Junk Science or Junk Food?" He writes that the new paper amounts to "the politicization of science."

Schillinger says that when you look at the body of evidence, the science is clear. "Nearly all experimental studies that examined whether eating added sugars contributes to obesity and [Type 2] diabetes-related outcomes show a cause-and-effect relationship," Schillinger told us.

Marion Nestle, a nutrition professor at New York University who has written extensively about the soda industry, says this new paper is an attempt by big food and beverage companies to use their power to undermine the scientific consensus on limiting added sugars in our diets.

"This is a classic example of industry-funded research aimed at one purpose and one purpose only: to cast doubt on the science linking diets high in sugars to poor health," Nestle tells us. "This paper is shameful."

The paper was funded by the International Life Science Institute. The group is financially supported by food and beverage companies including McDonald's Corp., Mars Inc., The Coca-Cola Co. and PepsiCo Inc.

"This is not an industry attempt to undermine the science," Eric Hentges, the executive director of ILSI, North America, told us. He says the aim of the paper is to examine the inconsistencies in sugar guidelines around the globe and to examine the science behind the specific recommendations. "The purpose of the paper was to investigate specifically the quality of methods and the quality of evidence," Hentges told us.

I asked study author Johnston for a specific example of a study that exemplifies the uncertainties in the scientific evidence on sugar intake. He pointed me to one published in the New England Journal of Medicine in 2012.

That study included 224 overweight and obese adolescents who regularly consumed sugar-sweetened beverages. The participants were divided into two groups. The experimental group received noncaloric beverages at home and were told to cut out sugar-sweetened beverages. The control group kept up their normal pattern of consumption.

At the end of the first year of the study, the participants who received the noncaloric beverages at home had smaller increases in body mass index compared with the control group. But by the end of the second year, "there was no difference between groups," Johnston says.

Johnston says the point he wants to make is that sugar intake is not the only factor related to obesity and Type 2 diabetes. "It's one factor among many," Johnston says. He says scientists should not put "ourselves into an ideological framework where we think that sugar is the scapegoat for the rise in obesity and diabetes."

The concern among public health experts is that this position — and this new paper published in Annals — could be used as a justification for questioning the dietary guidelines for sugar.

"The big picture here is we're talking about a fundamentally threatening [Type 2] diabetes epidemic," Schillinger told us. "Fourteen percent of Americans — that's 1 in 7 adults — have diabetes." And he says questioning the science behind specific recommendations should not distract from the effort to nudge people to consume less sugar.

Schillinger says this study and other industry efforts around sugar remind him of tactics used by Big Tobacco. "This is very reminiscent of what tobacco did around secondhand smoke," he says.

When studies showed harm related to secondhand smoke, "the [industry] called that science junk science. It was really an attempt to undermine the scientific process and create additional doubt in the general public," Schillinger says.

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