High Glycemic Index or High Carbohydrate Diet May Not Increase Risk of Insulin Resistance

Laurie Barclay, MD

June 06, 2005

June 6, 2005 -- A high glycemic index diet or a diet high in carbohydrates is not associated with increased risk of developing insulin resistance, according to the results of a study published in the June issue of Diabetes Care.

"Whereas observational studies suggest that intake of dietary fiber has an important role in determining insulin resistance, the precise nature of the relationships between glycemic index, glycemic load, simple sugars, total carbohydrate, and insulin resistance is uncertain," write Cathrine Lau, MSC, from the Steno Diabetes Center in Gentofte, Denmark, and colleagues from The Inter99 study. "The dietary recommendations given may therefore not be in favor of the prevention of insulin resistance in particular. The influence of carbohydrate-related dietary factors on insulin resistance thus needs further attention."

Investigators in the Inter99 study used baseline data and examined cross-sectional associations between carbohydrate-related dietary factors and an estimate of insulin resistance in 5,675 subjects aged 30 to 60 years. Dietary intake was estimated from a self-administered food frequency questionnaire, and insulin resistance was estimated using the homeostasis model assessment of insulin resistance (HOMA-IR). Multiple regression models of HOMA-IR vs carbohydrate-related factors were adjusted for age, sex, smoking, physical activity, total energy intake, body mass index, and waist circumference.

Although lactose intake was positively associated with HOMA-IR ( P < .0001), daily glycemic load and intake of glucose, fructose, dietary fiber, total carbohydrate, fruit, and vegetables were inversely associated with HOMA-IR ( P < .05). There were no significant associations for daily glycemic index or sucrose. Dietary fiber intake explained the associations with daily glycemic load and total carbohydrate and reduced the association with fruits and vegetables.

"Habitual intake of diets with a high glycemic index and high glycemic load or diets with a high content of total carbohydrate including simple sugars was not associated with the probability of having insulin resistance," the authors write. "Furthermore, intake of dietary fiber was inversely associated with the probability of having insulin resistance."

Possible study limitations may include selection or recall bias, inaccurate estimation of daily glycemic index, failure to consider the participants' glucose tolerance status, failure to account for genetic predisposition for obesity and type 2 diabetes; lack of specific questions regarding intake of soft drinks, juice, selected sweet products, and low-fat and fructose-rich products; and limited number of questions regarding intake of fruit and vegetables.

"These data are consistent with the hypothesis that intake of dietary fiber independent of obesity is important in prevention of insulin resistance," the authors write, while recommending large, observational, prospective studies. "Our findings therefore support the existing recommendations regarding increased intakes of fiber-rich carbohydrates, also with respect to prevention of insulin resistance."

The Danish Medical Research Council, the Danish Centre for Evaluation and Health Technology Assessment, Novo Nordisk, Copenhagen County, the Danish Heart Foundation, the Danish Diabetes Association, the Danish Pharmaceutical Association, the Augustinus Foundation, the Ib Henriksen Foundation, and the Becket Foundation supported this study. Three authors hold stock in and have received research support from Novo Nordisk.

Diabetes Care. 2005;28:1397-1403

Reviewed by Gary D. Vogin, MD

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