The mountain of scientific studies about the harms of excess dietary sugar is really just a house of cards—a flimsy stack of weak conclusions based on low-quality data. And the international dietary guidelines based on those studies—the ones urging people to cut back on sweets and sugary drinks—are disingenuous and cannot be trusted.

At least, that’s what a review out this week would have you believe. To get to those bold claims, the authors used questionable methods, subjective assessments, and money from the food and beverage industry. One of the lead authors is even on the scientific advisory board of Tate & Lyle, one of the world’s largest high-fructose corn syrup producers.

Health experts and researchers were quick to criticize the review—and its blatant bias. “Although scrutiny of dietary guidelines is warranted, we believe that this review is an example of the ‘politicization of science,’” Dean Schillinger and Cristin Kearns, health experts and researchers at the University of California, San Francisco, wrote in an accompanying editorial. “Politicization occurs when an actor overly accentuates inherent uncertainties of science to cast doubt on the scientific consensus.”

In other words, the recent review is kind of like gaslighting: the authors are trying to delegitimize and trivialize an entire body of peer-reviewed data and analysis, deny scientific consensus, and muddle our reality so that we question established conclusions.

This isn’t the first time the food industry has tried to mess with research for its own gains—it’s actually surprisingly common. In the 1960s, sugar industry executives secretly slipped hefty checks to unscrupulous Harvard researchers so that they’d downplay the role of sugar in heart disease. The move contributed to decades of dietary guidelines that emphasized cutting fats and cholesterols from your diet, but not sugars. This misinformation fed the popularity of low-fat (but potentially high sugar) diets and foods.

Now that independent researchers have established the harms of excess sugars, including their role in the current obesity epidemic, consumers are getting the message to cut back. So the sugar industry has its manipulative work cut out for it. Luckily, the press is tuned in to the potential threat of scientific subterfuge. Much of the media reports about the new review have noted the authors’ conflicts of interest and criticism from other researchers. However, the bravado with which the industry continues trying to influence research and the public’s perception is striking.

Sour science

The review, published in Annals of Internal Medicine, was sponsored by the International Life Sciences Institute (ILSI), a trade group funded by Coca-Cola, the Dr Pepper Snapple Group, Hershey, Mars, Nestlé USA, PepsiCo, Tate & Lyle, the Kraft Heinz Company, Unilever, and others. The two lead authors are Joanne Slavin, a food science and nutrition researcher at the University of Minnesota (and an advisor to Tate & Lyle), and Bradley Johnston of McMaster University.

Along with their colleagues, Slavin and Johnston tried to roast nine dietary guidelines from various health organizations and countries, including those of the US federal government and the World Health Organization. Their stated motivation to do so was that the guidelines weren’t all the same, which “can result in confusion and raises concern about the quality of the guidelines and the underlying evidence.”

However, as Schillinger and Kearns noted, the nine guidelines, which included 12 specific recommendations on sugar consumption, were written between 1995 and 2016—a lot of time for researchers to do research and experts to refine recommendations. All of the guidelines pushed for people to limit or reduce the amount of sugar they eat to prevent things like weight gain, cavities, and “nutrient displacement” (that is, eating candy when you could be eating something with nutrients, like fruits or vegetables).

But the guidelines differed on the extent to which to cut back. Recommended limits on “added” or “free” sugars (those added during food production) ranged between 25 percent and less than 5 percent of total energy consumed. However, the three most recent guidelines (all from 2015), by the US government, WHO, and Public Health England, were close in agreement—less than 10, 10, and 5 percent, respectively. Notably, the 2002 guideline that recommended the highest levels of added sugars (less than 25 percent) was partly funded by the ILSI.

With their targets selected, the authors then went about rating the guidelines and data behind them. They used two established evaluation methods: one designed to rate clinical practices for treating ill patients (not health guidelines); and another that the WHO used in assessing its own dietary guidelines. For the former, the authors invented their own scoring system of one to seven. And with the latter, the authors re-graded the WHO’s guideline and inexplicably lowered its scores. They argued that there were suddenly inconsistencies in body weight evidence among sugar studies, and they disagreed with WHO on evidence linking sugar to cavities.

In addition to the subjective assessments, the authors also made some puzzling ones. For instance, the authors criticized the US federal dietary guidelines for Americans because the funding source was “unclear,” despite the funding clearly coming from the federal government. The authors also gave the guidelines a bad grade for not making some of its data and methods publicly accessible, yet the feds posted an extensive online appendix that includes that information, plus a 500-page supplementary report, also online.

In all, the review concludes that: “the quality of available evidence to link sugar with health outcomes was generally rated as low to very low.”

In his criticism of the review, Barry Popkin, a nutrition professor at the University of North Carolina at Chapel Hill, told The New York Times that the authors “ignored the hundreds of randomized controlled trials” that documented the harms of excess sugar intake.

“They ignored the real data, created false scores, and somehow got through a peer review system that I cannot understand,” he said. “It is quite astounding.”

In a written statement to the press, Annals of Internal Medicine Editor-in-Chief Christine Laine said they decided to publish the review and the accompanying critical editorial because it was “of great interest” to their audience.

Annals of Internal Medicine, 2016. DOI:10.7326/M16-2020

Annals of Internal Medicine, 2016. DOI:10.7326/M16-2754 (About DOIs).