People with diabetes are advised to watch the amount of carbohydrates in their diet, but that may not be enough. The so-called glycemic index of food can also have a big impact on blood sugar levels.

Past research has shown that the effect on blood glucose levels of different foods with the same carbohydrate content can vary by as much as five-fold. This has led to foods being assigned a glycemic index. The glycemic index multiplied by the amount of carbs indicates the glycemic load of a particular food.

"The use of diets with low glycemic index in the management of diabetes is controversial, with contrasting recommendations around the world," Dr. Jennie Brand-Miller, of the University of Sydney, Australia, and associates note in the medical journal Diabetes Care.

To investigate further, they pooled the results of 14 clinical studies comparing the effects of diets with low versus high glycemic indexes on overall glycemic control in diabetic patients. Assessment of glycosylated hemoglobin (HbA1c) levels indicated the degree of control over a period of time.

The researchers report that "low-glycemic index diets reduced HbA1c by 0.43 percentage points over and above that produced by high-glycemic index diets."

They conclude that their analysis "provides objective evidence that targeting postprandial hyperglycemia via choice of low-glycemic index foods has a small but clinically useful effect on medium-term glycemic control in diabetics."

Nutrition and lifestyle approaches to diabetes prevention and treatment, they recommend, "should be given as much attention as drug therapies."