Researchers say that public health strategies to reduce consumption of sweetened beverages may be helpful because they create a greater risk of type 2 diabetes than most foods.
Sweetened beverages pose a greater risk of type 2 diabetes than most other foods that contain fructose – a naturally occurring sugar – according to a new BMJ report.
The results suggest that fruits – and other foods containing fructose – appear to have no harmful effect on blood glucose levels, while sweetened beverages and some other foods that add excess energy to diets can have detrimental effects.
"These findings may help guide recommendations on important dietary sources of fructose in the prevention and management of diabetes," said Dr. John Sievenpiper, lead author of the study and researcher at the Center for Clinical Nutrition and Modification of Risk Factors for St Hospital Michael in Toronto Canada.
"But the level of evidence is low and more high-quality studies are needed."
The role of sugars in the development of diabetes and heart disease attracts a wide debate, and growing evidence suggests that fructose can be particularly harmful.
Fructose occurs naturally in a variety of foods, including whole fruits and vegetables, natural fruit juices and honey. It is also added to foods such as soft drinks, breakfast cereals, baked goods, sweets and desserts under the "free sugars" guide.
Current dietary guidelines recommend reducing free sugars, especially fructose, from sweetened beverages. At present, it is not clear whether this should be the case for all food sources of these sugars.
As such, researchers based in St. Michael and the University of Toronto analyzed the results of 155 studies evaluating the effects of different dietary sources of fructose on blood glucose levels in people with and without diabetes. The test subjects were monitored for up to 12 weeks.
The results were based on four study designs: substitution (comparison of sugars with other carbohydrates), addition (energy of sugars added to the diet), subtraction (energy of sugars removed from the diet) or ad libitum (energy of freely substituted sugars).
Results were either glycated hemoglobin or HbA1c (amount of glucose bound to red blood cells), fasting glucose and fasting insulin (glycemia and insulin levels after a fasting period).
The results show that most foods containing fructose sugars do not have a detrimental effect on blood glucose levels when these foods do not provide excess calories. However, a detrimental effect was observed in fasting insulin in some studies.
Specific food analysis suggests that fruits and fruit juices when these foods do not provide excess calories can have beneficial effects on blood glucose and insulin control, especially in people with diabetes. However, foods that add "nutrient-poor" excess energy to the diet seem to have harmful effects.
Researchers conclude, "Until more information is available, public health professionals should be aware that the harmful effects of fructose sugars on blood glucose appear to be mediated by energy and food source."
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