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ARS Home » Northeast Area » Boston, Massachusetts » Jean Mayer Human Nutrition Research Center On Aging » Research » Publications at this Location » Publication #355403

Research Project: Cardiovascular Nutrition and Health

Location: Jean Mayer Human Nutrition Research Center On Aging

Title: Effect of macronutrients and fiber on postprandial glycemic responses and meal glycemic index and glycemic load value determinations

Author
item Meng, Huicui - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item Matthan, Nirupa - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item Ausman, Lynne - Jean Mayer Human Nutrition Research Center On Aging At Tufts University
item Lichtenstein, Alice - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2017
Publication Date: 2/15/2017
Citation: Meng, H., Matthan, N., Ausman, L., Lichtenstein, A.H. 2017. Effect of macronutrients and fiber on postprandial glycemic responses and meal glycemic index and glycemic load value determinations. American Journal of Clinical Nutrition. 105:842-885.

Interpretive Summary: Carbohydrate-containing foods differ in their effect on blood glucose concentrations. The concept of "glycemic index" was introduced to differentiate among foods based on blood glucose response to 50 g of carbohydrate during a 2-h period. The concept of glycemic load (GL) was introduced to adjust glycemic index for serving size. Meal or dietary glycemic index (GI) and glycemic load (GL) values from dietary questionnaires are often calculated using the GI values of individual foods and for GL after adjusting for serving size. Unaddressed is the potential confounding effect of different amounts and proportions of macronutrients across eating patterns. A series of four studies were conducted during which twenty participants received food challenges containing different amounts of the variable nutrient in a random order. Added to the standard carbohydrate from white bread was 12.5, 25 and 50 grams of carbohydrate from rice cereal, 12.5, 25 and 50 grams of protein from tuna, 5.6, 11.1 and 22.2 grams of fat from unsalted butter, and 4.8 and 9.6 grams of fiber from oat cereal. Adding carbohydrate to the standard white bread challenge significantly increased the meal GI and GL. Adding the highest amount of protein significantly decreased measured meal GI and GL. Adding fat or fiber had no significant effect on these parameters. These data indicate that uncertainty in meal GI and GL value determination is introduced when carbohydrate-containing foods are consumed concurrently with protein and carbohydrate, but not fat or fiber containing foods. Calculated meal GI and GL values should be used with caution.

Technical Abstract: Background: The potential confounding effect of different amounts and proportions of macronutrients across eating patterns on meal or dietary glycemic index (GI) and glycemic load (GL) value determinations has remained partially unaddressed. Objective: The study aimed to determine the effects of different amounts of macronutrients and fiber on measured meal GI and GL values. Design: Four studies were conducted during which participants [n = 20-22; women: 50%; age: 50-80 y; body mass index (in kg/m^2): 25-30)] received food challenges containing different amounts of the variable nutrient in a random order. Added to the standard 50 g available carbohydrate from white bread was 12.5, 25, or 50 g carbohydrate; 12.5, 25, or 50 g protein; and 5.6, 11.1, or 22.2 g fat from rice cereal, tuna, and unsalted butter, respectively, and 4.8 or 9.6 g fiber from oat cereal. Arterialized venous blood was sampled for 2 h, and measured meal GI and GL and insulin index (II) values were calculated by using the incremental area under the curve (AUCi) method. Results: Adding carbohydrate to the standard white-bread challenge increased glucose AUCi (P < 0.0001), measured meal GI (P = 0.0066), and mean GL (P < 0.0001). Adding protein (50 g only) decreased glucose AUCi (P = 0.0026), measured meal GI (P = 0.0139), and meal GL (P = 0.0140). Adding fat or fiber had no significant effect on these variables. Adding carbohydrate (50 g), protein (50 g), and fat (11.1 g) increased the insulin AUCi or II; fiber had no effect. Conclusions: These data indicate that uncertainty in the determination of meal GI and GL values is introduced when carbohydrate-containing foods are consumed concurrently with protein (equal amount of carbohydrate challenge) but not with carbohydrate-, fat-, or fiber-containing foods. Future studies are needed to evaluate whether this uncertainty also influences the prediction of average dietary GI and GL values for eating patterns.