It is well established that overconsumption of any food, especially foods that are high in sugar and fat, can lead to weight gain and an increased risk of type 2 diabetes. However, this increased risk of diabetes has always been linked to metabolic changes from weight gain and obesity.
Now a team of US-based researchers have suggested that sugar consumption itself may also have a direct relationship with our risk of developing diabetes.
Writing in PLoS One the team of researchers examined data on sugar availability and diabetes rates from 175 countries over the past decade, finding that that increased sugar in a population's food supply was linked to higher diabetes rates – even after they took account of obesity rates and a number of other factors.
"It was quite a surprise," said Professor Sanjay Basu, from Stanford University School of Medicine, who led the research team.
The study provides the first large-scale, population-based evidence for the idea that not all calories are equal from a diabetes-risk standpoint, said Basu.
"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.
Correlation or causation?
Basu emphasised, that the group’s findings do not prove that sugar causes diabetes, but said that they do provide real-world support for the body of 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," he said.
However, the American Beverage Association (ABA), said the study “does not show – or even attempt to show – that consuming sugar causes diabetes.”
“The study’s conclusions on sugar and diabetes should be viewed cautiously given that the underlying model failed to consider the potential impact of solid fats – such as butter, cheese and lard – or factor for family history,” said the ABA in a statement.
Dr Robert Lustig from the University of California-San Francisco, senior author of the study, noted that "epidemiology cannot directly prove causation."
A source of controversy
"As far as I know, this is the first paper that has had data on the relationship of sugar consumption to diabetes," commented Professor Marion Nestle of New York University, an independent nutrition expert who was not involved in the study.
"This has been a source of controversy forever,” she explained. “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," said Nestle.
The study used food-supply data from the United Nations Food and Agricultural Organization to estimate the availability of different foods in 175 countries and then compared these with estimates from the International Diabetes Foundation on the prevalence of diabetes among 20- to 79-year-olds in the same countries.
The researchers used new statistical methods derived from econometrics to control for factors that could provide alternate explanations for any apparent link between sugar and diabetes – including overweight and obesity; many non-sugar components of the food supply such as fibre, fruit, meat, cereals and oils; total calories available per day; rates of economic development; household income; and many more.
After adjusting for all of these possible other factors, the team found that sugar availability in the food supply at a national level has a significant and independent association with that countries incidence of type 2 diabetes.
Specifically, the team found that more sugar was correlated with more diabetes: For every additional 150 calories of sugar available per person per day, the prevalence of diabetes in the population rose 1.
In contrast, an additional 150 calories of any type was linked with just a 0.1% increase population diabetes rate.
Moreover, the longer a population was exposed to excess sugar, the higher its diabetes rate, the authors said – adding that diabetes rates also fell over time when sugar availability dropped in a particular nation.
Basu said the fact that the new paper used data obtained over time is ‘an important strength.’
"Point-in-time studies are susceptible to all kinds of reverse causality," he said. "For instance, people who are already diabetic or obese might eat more sugars due to food cravings."
The lead research said follow-up studies are now 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, he said, may be to conduct randomised clinical trial that could confirm a cause-and-effect connection between sugar consumption and diabetes.
Basu commented that although it would be unethical to feed people large amounts of sugar to try to induce diabetes, researchers may be able to randomise participants in to a low-sugar diet group to see if this reduces risk.