Excessive sugar consumption may be the main driver of a global rise in diabetes, independent of obesity, according to a study rekindling old debates about the sweetener’s role in an illness affecting 350 million worldwide.
Because diabetes levels are high in several countries with low obesity rates and vice versa, some scientists have theorized that rising consumption of processed, sugar-laden foods was a key driver of the diabetes epidemic. In a nutritional analysis of 175 countries published today in the journal PLoS One, researchers found that every 150 calorie increase in sugar was tied to a 1.1 percent boost in diabetes, after controlling for other foods, total calories, weight gain and sedentary lifestyles.
The study “adds another piece to the increasing evidence that everybody would be a lot healthier if they ate less sugar,” said Marion Nestle, a professor of nutrition, food studies and public health at New York University, who wasn’t involved in the study.
While the study doesn’t prove sugar causes diabetes directly, it shows that the longer a population was exposed to high levels of sugar, the higher its diabetes rate was after the researchers subtracted out other influences, such as physical activity.
Diabetes is caused by high levels of blood sugar. Symptoms include blurry vision, excess thirst and fatigue. Over time, diabetes can lead to trouble seeing, painful sores, amputation, and nerve damage.
The scientists, led by Robert Lustig, a pediatric endocrinologist at the University of California, San Francisco’s Benioff Children’s Hospital, used estimates from the United Nation’s Food and Agricultural Organization on the types of food typically eaten in 175 countries. They compared those numbers with the prevalence of diabetes among those ages 20 to 79, as estimated by the International Diabetes Foundation.
The group then used statistical methods to control for other conditions linked to diabetes, including the portion of the population older than 65, alcohol use, sedentary lifestyles and overweight and obese individuals. Even excluding those influences, the link between sugar and diabetes remained, Lustig said.
Sugars in food are broken into glucose, which is released into the bloodstream. The liver is the body’s glucose storage unit, and keeps the blood sugar levels constant. Insulin signals the liver to slow glucose production.
Excessively sugared foods can contribute to obesity through added calories, and may also increase the likelihood of diabetes by forming excess liver fat and starting inflammation, according to the study. That may in turn block the pathway insulin uses to stop the production of sugar, which may lead to insulin-resistance.
“People have been talking about sugar and diabetes for decades,” Lustig said in a telephone interview. “First the food industry said there was no relationship. Then in the 70s, they said, ‘Oh yes, we know sugar is associated with diabetes, but only because all calories are associated with diabetes, it’s an obesity issue.’”
This data shows otherwise, Lustig said.
His group used publicly available databases to see if anything in the food supply has changed in the past decade to explain the worldwide rise in diabetes rates. The only change they saw was an increase in sugar consumption, he said.
The study was editorially rejected from “virtually every journal,” before being published in PLoS ONE, Lustig said. He is known for his strident views on sugar, which he calls a toxin, and has published a book called “Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease.”
Because the study doesn’t directly control all variables save diet, it shouldn’t be taken as a final word, Nestle said. For decades, some scientists have held that eating too much sugar causes diabetes. Others believe that ingesting too many calories cause the illness.
“It’s really difficult to separate sugars from calories,” she said.
Elizabeth Seaquist, the president-elect of medicine and science for the American Diabetes Association, said more work needs to be done.
“It raises as many questions as it solves,” Seaquist said in a telephone interview. “There are so many limitations, trying to understand the source of the data. But the study does help us know this is a question worth pursuing.”
She suggested that a prospective study, controlling participants’ calories and changing the content of those calories would be the best way to pursue the question.
The databases used by Lustig’s group are “notoriously unreliable,” Nestle said. While they’re good at giving trends, they’re not accurate for absolute amounts of certain foods in the diet, she said. The numbers show the data on all the food in the country, less exports and plus imports, “so you can imagine how difficult it is to get that information accurately.”
Follow-up research to examine links between types of foods and obesity may help clarify the study’s observations, she said.
The study didn’t separate sugars that were eaten versus those people drank, nor did it distinguish between cane sugar and high fructose corn syrup. Seaquist, of the American Diabetes Association, also suggested looking at differences between types of sugars in future studies.