|Meng, Huicui - Jean Mayer Human Nutrition Research Center On Aging At Tufts University|
|Matthan, Nirupa - Jean Mayer Human Nutrition Research Center On Aging At Tufts University|
|Ausman, Lynne - Jean Mayer Human Nutrition Research Center On Aging At Tufts University|
|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: 1/9/2017
Publication Date: 2/15/2017
Citation: Meng, H., Matthan, N., Ausman, L., Lichtenstein, A. 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(4):842-853. https://doi.org/10.3945/ajcn.116.144162.
Interpretive Summary: Carbohydrate-containing foods differ in their effect on blood glucose concentrations. The concept of "glycemic index" (GI) was introduced to differentiate among foods based on blood glucose response to 50 grams of available carbohydrate during a 2 hour period. The concept of glycemic load (GL) was introduced to adjust for serving size. Individual values for GI have been used to calculate a GI index for meals or eating pattern and relate these data to health outcomes. When this is done, the potential confounding effect when the carbohydrate-containing food is consumed with other macronutrients is unaccounted for. Our aim was to determine the effect of different amounts of macronutrients and fiber on the GI and GL value added to a standard food: white bread. Four studies were conducted during which participants received the standard 50 grams of available carbohydrate from white bread with or without different amounts of carbohydrates, protein, fat, or fiber. Adding protein significantly decreased measured meal GI and GL. Adding carbohydrate, fat, or fiber had no significant effect on these parameters. These data indicate that uncertainty in meal GI and GL value determinations is introduced when carbohydrate-containing foods are consumed concurrently with protein but not 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.
Technical Abstract: Introduction: Meal or dietary glycemic index (GI) and glycemic load (GL) values from dietary questionnaires are calculated using GI values of individual foods and for GL after adjusting for serving size. Partially unaddressed is the potential confounding effect of different amounts and proportions of macronutrients across eating patterns. Objective: We determined the effect of different amounts of macronutrients and fiber on measured meal GI and GL values. Methods: Four studies were conducted during which participants (n=20-22, 50% female, 50-80y, BMI 25-30kg/m2) received food challenges containing different amounts of the variable nutrient in a random order. Added to the standard 50g available carbohydrate from white bread was 12.5, 25, 50g carbohydrate, 12.5, 25, 50g protein and 5.6, 11.1, 22.2g fat from rice cereal, tuna and unsalted butter, respectively, and 4.8, 9.6g fiber from oat cereal. Arterialized venous blood was sampled for 2h and measured meal GI, GL, and insulin index (II) were calculated using the incremental area under the curve (AUCi) method, and serum lipids determined using standard assays. Results: Adding carbohydrate to the standard white bread challenge incrementally increased glucose AUCi (p<0.0001), measured meal GI (p<0.0001) and GL (p<0.0001). Adding protein (50g only) decreased glucose AUCi (p=0.0026), measured meal GI (p=0.0139) and GL (p=0.0140). Adding fat or fiber had no significant effect on these parameters. Adding carbohydrate (50g), protein (50g) and fat (11.1g) increased insulin AUCi and/or II; fiber had no significant effect. Other serum parameters maintained unchanged. Conclusions: These data indicate variability in measured meal GI and GL values is introduced when carbohydrate containing foods are consumed in different amounts or concurrently with protein (equal amount of carbohydrate challenge) but not fat or fiber. These conclusions raise the issue of whether GI of individual foods should be used to calculate average dietary GI and GL values for eating patterns.