Methodology for adding glycemic load values to the National Cancer Institute Diet History Questionnaire database.

BACKGROUND: A growing interest exists in using glycemic index and glycemic load as potentially important exposures in investigations of risk for a variety of chronic diseases.
OBJECTIVE: We added values for glycemic index and glycemic load to the nutrient database of a commonly used dietary assessment instrument, the Diet History Questionnaire (DHQ).
DESIGN: The nutrient database for the DHQ is based on 4,200 individual foods reported by adults in the 1994-1996 US Department of Agriculture Continuing Survey of Food Intakes by Individuals (CSFII). This list was condensed into 225 nutritionally similar groupings of individual foods. Using published glycemic index values we assigned glycemic index values to each of the individual CSFII foods in these food groups. In cases where CSFII foods did not correspond tightly to foods with published glycemic index values, we used decision criteria to assign glycemic index values. We then calculated sex- and serving size-specific glycemic load for each of the 225 food groups using the weighted mean method. Quality assessments were made to help evaluate the success of this method for assigning glycemic load values.
RESULTS: Seventy-one percent of the top carbohydrate-contributing food groups had in excess of 90% of the CSFII mentions linked directly to a published glycemic index value (ie, no imputation was required), and 100% of these food groups had at least 50% of total mentions linked directly.
CONCLUSIONS: Using this method, it is now possible to use DHQ responses to assess the associations between reported glycemic load and glycemic index and risk of many chronic diseases in epidemiologic studies.