Scientists at the University of California, San Francisco, said they have uncovered documents demonstrating that members of the sugar industry called off a study, named Project 259, in the 1960s because it linked sucrose — a common sugar — to heart disease and bladder cancer in preliminary experiments.

In 2016, the same researchers discovered a separate, undisclosed document that showed the sugar industry funded a report that downplayed links between sugar and coronary heart disease.

But a trade group argues the sugar industry was always transparent about Project 259 and that it supports science-based evidence even if the results are unfavorable. Here’s a breakdown of what UCSF researchers found.

How the researchers spotted Project 259

UCSF dentist Cristin Kearns started digging into the sugar industry 10 years ago, after representatives at a conference said there is “no scientific consensus” that sugar is linked to chronic illnesses. She combed through library archives across the nation and eventually stumbled across a box containing “confidential” documents on “Project 259.”

In 1968, the Sugar Research Foundation launched a rodent study, which measured the nutritional products of gut bacteria after rats consumed sucrose compared to starch. Project 259’s early results showed that sucrose caused gut microbes to throw off the rodents’ metabolisms, increasing their levels of triglycerides. Triglycerides are fatty molecules, which when elevated, can clog arteries and predispose a person for cardiovascular disease. In a preliminary experiment, Project 259 also found a high-sugar diet boosts the activity of beta-glucuronidase, an enzyme linked to bladder cancer, when compared to a starch diet. The second half of the study, which would have taken a deeper look at starch, was never finished.

After reporting this discovery in August 1970 to the International Sugar Research Foundation, Project 259 scientists requested an additional 12 weeks of funding to continue the research, according to internal documents. One month later, Sugar Research Foundation’s Vice President of Research John Hickson described the value of Project 259 as “nil,” Glantz and Kearns state. The funding request was denied, and the project was abandoned in 1971.

Kearns and UCSF cardiologist Stanton Glantz, who revealed the project’s details in an analysis published Tuesday in PLOS Biology, argue that the sugar industry buried the evidence and stopped funding due to the negative findings.

What the sugar industry says: Courtney Gaine, the president and CEO of the Sugar Association, said the researchers’ assessment is nothing more than, “a series of assumptions and speculations.”

“They never called us. We would have let them look at the archives. I would let them look tomorrow. The story we have in our archives is a lot better than the story they’ve been telling,” Gaine said.

Gaine said her own internal investigation found that Project 259 was cancelled right when the Sugar Research Foundation was dividing into two organizations: the Sugar Association and the International Sugar Research Foundation (which is now World Sugar Research Organization). Adding to the bureaucratic shuffle, the study suffered from long delays and going significantly over budget, Gaine said. (Glantz, in opposition, argued that such delays are inherent to research).

Project 259 was ultimately handed over to the British Nutrition Foundation to complete, Gaine said, and added that her documentation ends there. She said the Sugar Association doesn’t know why the British Nutrition Foundation failed to complete the study.

Why this matters: “Evidence was emerging in the 1950s and 1960s that linked sugar consumption to heart disease, but the sugar industry was interested in casting doubt on that evidence. In [Project 259] they were proving that to themselves and then saying something different to the public,” University of California’s Kearns said.

Gaine countered that the Sugar Association wasn’t trying to hide anything. When it comes to sugar, “there has always been an understanding that there is too much of a good thing,” she said, arguing that the industry looks into any negative health claims because they “want to know if they are accurate.”

Gaine added that the Sugar Association supports the dietary guidelines of sugar in moderation based on the FDA recommendation that only 10 percent of daily caloric intake should come from sugar. She also pointed out one of the funders for Glantz and Kearns’ investigation is Gary Taubes, co-founder of Nutrition Science Initiative and author of the book “The Case Against Sugar.” Another funder — the Laura and John Arnold Foundation — once gave $500,000 to support a lawsuit in favor of taxes on sugary beverages.

But, Kearns believes that had the preliminary results been confirmed and published, it would have caused more scrutiny of sugar as a carcinogenic food additive. In the late 1960s, artificial sweeteners were being examined over similar concerns. A 1969 study found cyclamate, an artificial sweetener, increased the risk of bladder cancer in rats, and this sweetener was banned shortly afterward.

Both Gaine and Glantz said Project 259 was cutting edge for its time, given its focus on the gut microbiome. Kearns said that completing Project 259 and disclosing its findings could have hastened the onset of “precision medicine” — developing targeted interventions for people with heart disease based on their risk factors. This customized health care considers, for example, looking at the blood profile (cholesterol and triglycerides) to recommend either a low fat or a low sugar and carb diet.

“Whether you are talking about the sugar industry, or tobacco, or oil industry and climate change — the basic game they are playing is to try to slow down the development of a strong scientific consensus that could drive policy change,” Glantz said.