Abstract 12195: Carbohydrate and Protein but not Fat or Fiber Affects Glycemic Index and Glycemic Load Value Determinations

Abstract

Introduction: Dietary glycemic index (GI) and glycemic load (GL) values have been calculated using data derived from instruments designed to estimate daily food intake. Since the absolute amount of carbohydrate (CHO) and combination of CHO with other macronutrients and fiber is highly variable among dietary patterns, the accuracy of these values is uncertain. This issue is of concern when dietary GI and GL values are used to identify diet/health outcome associations. Hypothesis: Increasing amounts of macronutrients (CHO, protein and fat) and fiber added to a test CHO challenge (50g available CHO) from white bread (WB) will alter GI and GL values. Methods: The trial included 4 studies, during which subjects (n=20-22, 50% female, 50-80y, BMI 25-30kg/m 2 , free from chronic disease and having fasting glucose levels ≤125mg/dL) received food challenges containing different amounts of the variable nutrient in a random order. In all studies, a glucose drink (50g available CHO/500mL) was used as the reference food. Studies 1-3 consisted of 4 food challenges, containing WB (50g available CHO+500mL water) alone or with additional CHO (12.5g, 25g, 50g), protein (12.5g, 25g, 50g) and fat (5.6g, 11.1g, 22.2g) from Rice Chex breakfast cereal (General Mills), tuna, and unsalted butter, respectively. Study 4 consisted of 3 food challenges, containing WB alone or with additional fiber (4.8g, 9.6g) from Cheerios (General Mills). Arterialized venous blood was sampled at 0, 15, 30, 45, 60, 90 and 120 minutes, and GI and GL values were calculated using the recommended incremental area under the curve (AUC) method. Results: Addition of 12.5g, 25g and 50g additional CHO to WB incrementally increased glucose AUC (p<0.0001), GI (p<0.0001) and GL (p<0.0001) values; while addition of protein (50g) to WB decreased glucose AUC (p=0.0026), GI (p=0.0139) and GL (p=0.0140) values. Addition of fat or fiber to WB had no significant effect on any measure. Conclusions: These data indicate that variability in postprandial GI and GL values is introduced when CHO containing foods are consumed in different amounts or in combination with protein. These conclusions raise the issue of whether GI and GL values from individual foods should be used to calculate dietary GI and GL values from dietary intake data.