New research has found that sugar in sweetened drinks could be more harmful for health than sugar found naturally in foods such as whole fruit, possibly increasing the risk of type 2 diabetes.

Carried out by Canadian researchers, including a team at St. Michael's Hospital in Toronto, the new review analyzed 155 studies with a total of 5,086 participants, investigating the effect of different sources of fructose sugars on the blood glucose levels in participants with and without diabetes.

Fructose is a sugar which occurs naturally in a range of foods, including whole fruits and vegetables, natural fruit juices and honey, but is also added to foods such as soft drinks, breakfast cereals, baked goods, sweets, and desserts as ‘free sugars.'

The findings, published by The BMJ, suggest that sweetened drinks and some other fructose-containing foods may have harmful effects on blood glucose levels, which can increase the risk of type 2 diabetes.

Diabetes is a chronic disease that occurs either when the pancreas does not produce enough insulin -- the hormone that regulates blood sugar -- or when the body cannot effectively use the insulin it produces.

However, fruit and other foods containing naturally-occurring fructose appeared to have no harmful effect on blood glucose levels.

In fact, the researchers found fruit and fruit juice may have beneficial effects on blood glucose and insulin control, especially in people with diabetes, possibly due to the high fiber content of fruit helping slow down the release of sugars.

Current guidelines already advise limiting consumption of free sugars, especially those found in sweetened beverages, with increasing evidence suggesting that fructose could be harmful to health.

However, the researchers noted that the review does have some limitations, including small sample sizes in the included studies, short follow-up periods, and with some studies including a limited variety of foods.

"These findings might help guide recommendations on important food sources of fructose in the prevention and management of diabetes," said Dr. John Sievenpiper, the study's lead author. "But the level of evidence is low and more high quality studies are needed."