Dietary Assessment Primer

Learn More about Software for Dietary Analysis of Food Frequency Questionnaires and Screeners

Computer programs—software—are used to translate reported dietary intakes from food frequency questionnaires (FFQ) and frequency-based screeners into variables of interest (see Food Frequency Questionnaire Profile and Screeners Profile). FFQs consist of questions about usual frequency of consumption by day, week, month, or year of each food and beverage queried. Some FFQs ask about frequency in season and the rest of the year. FFQs also may include separate questions regarding usual portion size of each item. Additionally, FFQs can include general questions related to additions to foods (such as fats or sweeteners), types of fats or sweeteners usually consumed, or usual versions of foods consumed (such as regular vs. decaffeinated soda). Finally, many FFQs collect information about intakes of supplements over a defined time period. Frequency-type screeners generally consist of questions about usual frequency of consumption of a limited list of foods and beverages, and do not include questions about supplements.

  • First, the software uses algorithms to assign daily frequency of use to each food or beverage item, including seasonal information if available.
  • Second, usual portion size, either predetermined or based on answers to portion size questions if included, is calculated, and expressed in terms of grams per eating occasion. This process is carried out for each food and beverage item, applying answers to questions regarding additions and types of foods when applicable. Each item's portion size requires conversion of the common household units listed in the FFQ (such as cups, volume in ounces, slices) into gram weights. These gram weights are specific to each food and beverage item queried and often represent a weighted average of portion sizes reported in an external data set of recalls or records (for example, a gram weight portion size for cheese based on many types and portion sizes reported in the [glossary term:] National Health and Nutrition Examination Survey (NHANES)) or a "standard" portion.
  • Third, daily frequencies are multiplied by the estimated usual portion size per eating occasion to derive the daily grams reported for each food and beverage item.
  • Fourth, a database linking each FFQ line item to food composition information is necessary (Learn More about Food Composition Databases for Food Frequency Questionnaires and Screeners). For each food and beverage queried, the product of daily frequency and gram weight portion size is multiplied by the appropriate nutrient or food group composition values to obtain the daily intake. These are then summed across all foods for each nutrient and food group for each individual to get an estimated total daily intake from food and beverages.

If supplement information is collected, software is needed to convert that information into average daily intake. This source of intake can be added to the intake from foods to estimate the [glossary term:] total nutrient intake (Learn More about Dietary Supplements and Estimating Total Nutrient Intakes).

Most food frequency instruments have software packages to compute these daily totals. Users should be aware of the source of information in the food composition database and the assumptions about the nutrient content of each food item listed in the questionnaire.

For More Information

Diet History Questionnaire. National Cancer Institute.

Thompson FE, Subar AF. Chapter 1, Dietary assessment methodology, Chapter 1 in Nutrition in the Prevention and Treatment of Disease. Third Edition. Coultson AM, Boushey CJ, Ferruzzi MG, ed. Elsevier Press: San Diego, CA. 2013.