New research suggests that drinking sugar-sweetened beverages, such as cola, likely boost your risk of type 2 diabetes much more than the sugar found in fruit or even 100 percent fruit juices.
"All foods are not created equal," said study author Dr. John Sievenpiper, an associate professor and staff physician at the University of Toronto and St. Michael's Hospital in Canada.
"We synthesized all of the available trials looking at different food sources of sugar and blood sugar control, and sugar-sweetened beverages really stand out as having an adverse effect," he explained.
Sievenpiper said that 100 percent fruit juice can be healthful if it doesn't add excess calories to the diet.
"Fruit juice can complement fruit and vegetable intake," he noted, "but if you use fruit juices to stay hydrated, there is some risk."
Meanwhile, fruit appeared to have a protective effect on blood sugar levels, along with providing important nutrients and fiber, he said.
The effects of sugar in the diet have been hotly debated for decades. In recent years, the debate has been reignited by the parallels between the consumption of high-fructose corn syrup (a concentrated form of sugar used in many products, including soft drinks) and the rise of obesity and diabetes in the United States, according to the study authors.
To see if the type of sugars consumed has an effect on type 2 diabetes risk, the researchers reviewed data from 155 nutritional studies. All looked at the effects of foods on blood sugar levels in people with and without diabetes. The studies monitored volunteers for as long as 12 weeks.
The investigators found that fruits and fruit juices seemed to have beneficial effects on insulin and blood sugar control, especially in people with diabetes, as long as they didn't provide excess calories in the diet. So, if someone needs 2,000 calories a day to maintain their weight, a small glass of orange juice that doesn't cause that person to go over 2,000 calories is probably fine.
But foods that contain few nutrients, such as sugar-sweetened beverages, and fruit juice that provide excess calories in the diet seem to have harmful effects on blood sugar levels, the researchers said.
"If you consider your daily caloric allotment, you don't have a lot of calories to spare, so it's important to think about what a food is giving you. Foods that don't have redeemable qualities like fiber should really be considered discretionary foods. Sugar-sweetened beverages are just pure calories," Sievenpiper said.
It's important to consider the whole food, he explained. For example, if you're eating a high-fiber cereal that has a little bit of sugar, "that's probably OK," he said.
Registered dietician Samantha Heller from NYU Langone Health reviewed the findings.
"Sugars from natural sources like fruits are part of a healthy diet and necessary for life -- we need it for fuel for cells and muscles. What we don't need are highly processed foods. We need to eat less highly processed foods. We're better off with real foods," she said.
"It's all about balance. Fruits are part of a healthy, balanced diet. They're loaded with antioxidants and fiber, but like any other food, fruit can become a problem when we eat it in excess," Heller added.