The link between sugar and chronic diseases like obesity and type 2 diabetes is well established, but even though many public health groups recommend limiting sugar intake, they differ widely on the recommended daily limits.
The most recent U.S. dietary guidelines recommend Americans get less than 10% of their daily calories from added sugars—which is roughly the equivalent of a 16-ounce soda. The World Health Organization has issued similar guidelines, while other groups say 25% of total calories should be the cap.
Complicating things is a new study published Monday in the Annals of Internal Medicine, where researchers looked at the evidence used to support daily sugar limits of less than 10% of a person's total calories. Ultimately, they concluded that those public health recommendations were based on low-quality science.
So does that imply that sugar should get carte blanche in the American diet?
Not exactly, say the researchers. "Although our findings question the recommendations from guidelines produced by leading authorities, the findings should not be used to justify high or increased consumption of nutrient-poor, energy-dense foods and beverages like candy and sugar-sweetened beverages," said Bradley Johnston, principal investigator of the review, in a statement.
Still, some researchers expressed concern about the trustworthiness of the new findings since the research was funded by the North American branch of the International Life Sciences Institute (ISLI), a trade group whose board is made up of scientists as well as representatives for major food and beverage companies. ISLI members include Coca-Cola Company, The Hershey Company, Dupont, Mars, Inc., Monster Energy Company, Nestlé USA, PepsiCo and more. (You can see the organization's membership list here.)
"Our concerns about the funding source and methods of the current review preclude us from accepting its conclusion that recommendations to limit added sugar consumption to less than 10% of calories are not trustworthy," writes Dr. Dean Schillinger, a professor of medicine at the University of California San Francisco (UCSF) in a corresponding editorial in the same journal. "Policymakers, when confronted with claims that sugar guidelines are based on 'junk science,' should consider whether 'junk food' was the [funding] source."
The authors of the new study say they conducted the study without input from the International Life Sciences Institute. "However, given our funding source, our study team has a financial conflict of interest and readers should consider our results carefully," the authors wrote in their conclusion.
A separate Nov. 2016 study, lead by Schillinger, found that industry-funded studies are significantly less likely to connect sugar or sugary beverages to bad health outcomes than studies funded by independent researchers. It was the latest in a series of recent reports about the connection between the sugar industry and researchers.
A Sept. 2016 report by Dr. Cristin Kearns, a dentist turned investigative researcher at UCSF, found that the sugar industry sponsored research that blamed fat for heart disease rather than sugar. Another report by Kearns found that sugar industry advocacy groups influenced federal cavity prevention recommendations through strategies like getting sugar experts on federal panels concerning tooth decay.
Today, the food industry funds a lot of health research. As one example, a recent study published in the American Journal of Preventive Medicine reported that between 2011 to 2015, more than 95 national health organizations accepted money from Coca-Cola or PepsiCo or both.
When asked why they chose to publish the new industry-funded study, the editors of the Annals of Internal Medicine sent this statement by email:
"Annals decided to publish the paper because the topic of sugar consumption is one that is of great interest to Annals readers and their patients. The fact that recommendations differ substantially is confusing for clinicians, their patients, and the public in general...
Despite what the editorial implies, the authors of the study do not conclude that intake of any amount of sugar is healthy. Rather, the authors conclude—and provide evidence to support this conclusion—that guidelines about sugar consumption are based on weak evidence and we need better research on this topic."