Yet the study itself was never published and has been forgotten until now.
"All we know is that the plug got pulled and nothing got published," said Stanton Glantz, a professor of medicine at the University of California, San Francisco and a co-author of the new paper.
"Whether the investigator didn't bother to try or whether he tried and failed, we don't know. Or whether there was some kind of clause in his agreement with the sugar people that precluded him from publishing, we don't know," he said.
This enigmatic study seems to provide evidence of the harmful health impacts of eating too much sugar. It also suggests that a group then called the Sugar Research Foundation might have manipulated scientific research in its favor, according to the new paper.
The authors of the new paper previously conducted a separate historical analysis of sugar industry-related documents and studies.
That analysis, published last year in JAMA Internal Medicine
, suggested that the Sugar Research Foundation sponsored a research program that successfully cast doubt about the health hazards of a high-sugar diet and rather promoted fat "as the dietary culprit" in health concerns such as heart disease.
"The kind of science manipulation that the tobacco industry engaged in is exactly the same kind of behavior that we've documented in these papers from the sugar industry," said Glantz, who has also studied the tobacco industry
How a forgotten study gets found
The foundation, now called the Sugar Association
, spoke out against that analysis last year and has contested the new PLOS Biology paper, telling CNN that it's "not actually a study, but a perspective: a collection of speculations and assumptions about events that happened nearly five decades ago, conducted by a group of researchers and funded by individuals and organizations that are known critics of the sugar industry."
The association also noted that the study described in the new paper ended without publication partly due to being "significantly delayed" and "consequently over budget."
"We don't know what would have happened had this study come out differently and showed no effect of sugar," Glantz said. "I would bet that it would have been published, and they would be thumping the drums about it."
Cristin Kearns, an assistant professor at the UCSF School of Dentistry
and lead author of the paper, said she learned about the long-lost study while collecting and analyzing letters between executives at the Sugar Research Foundation and various scientists from 1959 to 1971.
Then she noticed that the study was mentioned in a separate book that was published by the Sugar Research Foundation, which she found in a public library.
The book "listed all of their research projects between 1943 and 1972, and this project was listed in their report," Kearns said. "This particular project didn't have any publications, and so that made me curious about wanting to understand more about the project."
The study was called Project 259
, and the Sugar Research Foundation initially authorized 15 months of funding for it from June 1968 to September 1969, according to the paper.
As Kearns learned more about Project 259, she discovered that the study resulted in two findings in rats that, had funding been extended, would have been unfavorable to the sugar industry's commercial interests, according to the paper.
The 'fascinating' findings
First, the study showed that the urine of rats fed a high-sugar diet appeared to have higher levels of an enzyme called beta-glucuronidase than the urine of rats fed a basic diet high in starch, according to the paper.
Beta-glucuronidase has been associated with an increased risk of bladder cancer
"That was of some policy relevance at the time, because there was something called the Delaney clause
, which said the FDA was supposed to keep carcinogens out of the food supply even if they were animal carcinogens," Glantz said.
Congress passed the Delaney clause in 1958
to prohibit the approval of any food additives
shown to induce cancer in humans or animals.
Project 259 also showed a statistically significant decrease in triglycerides
, a type of fat in blood, in rats that were fed a high-sugar diet and were stripped of bacteria in their guts, compared with conventional rats fed a basic diet. Colonies of bacteria in your gut are known as the gut microbiome.
"Basically, they found that to get that elevated triglyceride response in the blood in rats that were fed a high-sugar diet, there needed to be bacteria in the gut," Kearns said.
"So without the bacteria, you didn't get the high triglyceride response, and so this proved to them at the time that the gut microbiome had a role in this elevated triglyceride response to eating sugar," she said. "I thought this is a fascinating study that they were even considering the role of the gut microbiome back as far as the 1960s."
Yet a limitation of the new paper is that it turns the spotlight on an animal study, and how sugar impacts rats may not exactly mirror how it could impact humans.
On the other hand, "I think doing animal studies is an important way to help understand the mechanisms of disease," Kearns said. "While obviously, a rat is not exactly the same as a human, it allows you to conduct experiments in a certain way to learn things that can influence future studies."
The sugar industry responds
In its written statement to CNN, the Sugar Association noted that the authors of the new paper did not reach out to it to verify any of their claims.
"We reviewed our research archives and found documentation that the study in question ended for three reasons, none of which involved potential research findings: the study was significantly delayed; it was consequently over budget; and the delay overlapped with an organizational restructuring with the Sugar Research Foundation becoming a new entity, the International Sugar Research Foundation," the association's statement said.
"There were plans to continue the study with funding from the British Nutrition Foundation, but, for reasons unbeknown to us, this did not occur," the statement said.
In response, Kearns pointed out that other studies that overlapped with that organizational restructuring were still continued.
The Sugar Association's statement added that sugar consumed in moderation can be part of a balanced lifestyle and that the association remains committed to supporting research to further understand the role sugar plays in consumers' diets.
Why the timing is 'concerning'
All in all, the new paper's findings were "striking" and "ethically concerning" to Dr. Sanjay Basu, an assistant professor of medicine at Stanford University
who was not involved in the work.
"The context for this historically is that during the time at which these studies were taking place, a lot of dietary recommendations were being formulated that emphasized reducing high-fat foods in particular, and in many cases low-fat foods were replaced by high-sugar foods to be more palatable," said Basu, who has studied the health impacts of added sugars
in his own research.
"The fact that sugar was not being considered an additionally concerning substance unfortunately led to a lot of changes in the American diet that correspond to a rise in obesity and type 2 diabetes," Basu said.
"So the suppression of this type of study is partly greatly concerning because of the time in which it took place," he said. "Although we're not sure what a safe amount of added sugar is, it's pretty clear and increasingly apparent that we're well above what might be considered reasonable in terms of our added sugar consumption as a country."