Researchers have thought for years that eating too much of any food can cause weight gain and predispose people to diabetes. But a Stanford University School of Medicine study has now linked sugar directly and independently to diabetes.
After accounting for obesity and other factors, researchers discovered that increased sugar in a population's food supply correlated with higher rates of type 2 diabetes. Scientists from Stanford University School of Medicine, the University of California, Berkeley, and the University of California, San Francisco, examined data on access to sugar and diabetes rates from 175 countries during the past decade. The research was published last week in PLOS ONE, a scientific journal.
The research provides the first evidence drawn from a large-scale population study for the idea that not all calories are equal when it comes to risk of diabetes, said Dr. Sanjay Basu, an assistant professor of medicine at the Stanford Prevention Research Center and the study's lead author.
"It was quite a surprise. We're not diminishing the importance of obesity at all, but these data suggest that at a population level there are additional factors that contribute to diabetes risk besides obesity and total calorie intake, and that sugar appears to play a prominent role," he said.
More sugar was associated with more diabetes, according to the research. For every additional 150 calories of sugar available per person per day, the prevalence of diabetes rose 1 percent, even after taking into account obesity, physical activity, other types of calories and economic and social factors. A 12-ounce can of soda contains about 150 calories of sugar. In contrast, an additional 150 calories of any type caused only a 0.1 percent increase in diabetes rate, according to the research.
Not only was a population's access to sugar associated with diabetes risk, but the longer a group was exposed to excess sugar, the higher its diabetes rate after controlling for obesity and other factors. Diabetes rates dropped over time when the availability of sugar dropped, independent of changes to consumption of other calories and physical activity or obesity rates, researchers said.
The findings do not prove that sugar causes diabetes, Basu emphasized, but do support previous laboratory and experimental trials that suggest sugar affects the liver and pancreas in ways that other types of foods or obesity do not.
"We really put the data through a wringer in order to test it out," Basu said.
The study used food-supply data from the United Nations Food and Agricultural Organization to estimate the availability of different foods in the 175 countries and estimates from the International Diabetes Foundation on the prevalence of diabetes among 20- to 79-year-olds.
Marion Nestle, a professor of nutrition, food studies and public health at New York University who was not involved in the study, praised the research.
"As far as I know, this is the first paper that has had data on the relationship of sugar consumption to diabetes. This has been a source of controversy forever. It's been very, very difficult to separate sugar from the calories it provides. This work is carefully done, it's interesting and it deserves attention," she said.
Basu said follow-up studies are needed to examine possible links between diabetes and specific sugar sources, such as high-fructose corn syrup or sucrose, and also to evaluate the influence of specific foods, such as soft drinks or processed foods.
Another important future step is to conduct clinical trials that could support a cause-and-effect connection between sugar consumption and diabetes. It would be unethical to feed people large amounts of sugar to try to induce diabetes, but scientists could put participants of a study on a low-sugar diet to see if it reduces diabetes risk.
Basu was cautious about possible policy implications of his work. More evidence is needed before enacting widespread policies to lower sugar consumption, he said.
But Nestle pointed out that the findings add to many other studies that suggest people should cut back on their sugar intake.
"How much circumstantial evidence do you need before you take action? At this point we have enough circumstantial evidence to advise people to keep their sugar a lot lower than it normally is," she said.
The study is available online at PLOS ONE.