The 1960s study, which suggests a link between a high-sugar diet and high blood cholesterol levels and cancer in rats, was sponsored by the sugar industry, according to the perspective paper published in the journal PLOS Biology on Tuesday.
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 newpaper.
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.
"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.
"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."
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