In the 1960s, a debate began over the effect of sugar and fats on cardiovascular disease. Researchers say that the sugar industry, wanting to influence the discussion, funded research to look into sugar consumption.

And when it found data suggesting that sugar was harmful, the powerful industry pointed a finger at fats.

In an investigation published Tuesday in the journal PLOS Biology, researchers from the University of California at San Francisco claim that newly uncovered historical documents indicate the industry never disclosed the findings of its work and effectively misled the public to protect its economic interests.

After examining the sugar industry’s internal documents, UCSF researchers said that in 1968 the Sugar Research Foundation, which has organizational ties to the Sugar Association, funded animal research to explore the link between sugar consumption and cardiovascular disease. Rats were fed a high-sugar diet — and were found to have increased levels of triglyceride, fatty substances in the bloodstream. In humans, high triglyceride levels can increase the risk of heart attack or stroke.

The research also found a connection between sugar consumption and an enzyme associated with bladder cancer.

In their investigation, the UCSF researchers said it is likely that the Sugar Research Foundation was unhappy with findings associating sugars with chronic disease, and what those findings could mean for humans. So it chose to end the study and did not publish its results, the researchers said.

One of the investigation’s authors, Stanton Glantz, told the New York Times that while the documents are several decades old, they are significant, as they show how long the sugar industry has spent de-emphasizing sugar’s effect on health.

“This is continuing to build the case that the sugar industry has a long history of manipulating science,” he said.

Glantz could not be immediately reached for comment.

The Sugar Association criticized Tuesday’s report and said in a statement that it was not a study but a perspective, “a collection of speculations and assumptions about events that happened nearly five decades ago.” It also called the researchers “known critics of the sugar industry.”

The sugar industry has long denied that sugar has any specific role in chronic disease, though research suggests otherwise. The Sugar Association issued a statement in early 2016 criticizing a University of Texas MD Anderson Cancer Center study suggesting that sugar in Western diets increased the risk of breast cancer tumours and metastasis.

The researchers’ claims that the sugar industry misled the public mirror accusations the tobacco industry faced. A trial was held in 2004 to determine whether tobacco industry officials had intentionally deceived Americans for years into thinking that smoking did not cause cancer, despite acknowledging the dangers of smoking among themselves.

Eight months later, the tobacco industry was asked to pay $10 billion (U.S.) over five years to help millions of Americans quit smoking. The penalty was less than 8 per cent of what the government had asked for when proceedings began.

Tuesday’s report isn’t the first time that decades-old documents appear to show that the sugar industry distorted medical research. A 2015 report published in the journal PLOS Medicine described a national campaign in the 1960s to boost cavity prevention and a government research program created to curb tooth decay by the 1970s. But instead of encouraging people to eat less sugar, the government — swayed by sugar industry interests — pushed alternative methods such as ways to break up dental plaque and vaccines for fighting tooth decay.

In 1964, the group now known as the Sugar Association looked for ways to soften “negative attitudes toward sugar” after studies began linking sugar with heart disease. The group approved “Project 226,” in which it paid Harvard researchers today’s equivalent of $48,900 to write an article reviewing those studies. The article, published in 1967, concluded that there was “no doubt” that the only dietary intervention needed to prevent heart disease was reducing cholesterol and saturated fat. The researchers played down the effects of sugar, according to an analysis of historical documents published in the journal JAMA Internal Medicine.

The Sugar Association said the 1960s research cited in Tuesday’s report ended for three reasons: It was too expensive, it was “significantly delayed,” and the delay interfered with the organizational restructuring of the Sugar Research Foundation, which would eventually become the International Sugar Research Foundation.

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Cristin Kearns, an author of the investigation, told NPR that the sugar industry continues to have “a lot of money and influence,” which it uses to downplay nutrition guidelines, such as those limiting added sugars to no more than 10 per cent of daily caloric consumption.

Had the data found in the 1968 study been made public, sugar may have been looked at under a more critical lens in the years since, she said.