Measurement of Food Intake
SACHIKO T. ST. JEOR
The assessment of food intake is challenging since food choices, quantity of foods eaten, and eating patterns are highly variable. Furthermore, complex interactions between what is eaten and physiological cues, psychological status, behavioral factors, and environmental opportunities are subtle and not well understood. However, understanding why, when, what, and how we eat is critical to identifying the etiology, diagnosis, and most effective treatment for eating disorders and obesity. Thus, this chapter outlines the basic methods for measuring food intake and provides information relevant to data collection, analysis, and interpretation.
There are five basic methods for assessing dietary intake.
1. Diet histories. These usually take the form of questionnaires of varying length and detail, and provide general information regarding usual dietary intake, food preferences, and associated behavior. A 24-hour recall is often included (see below). Diet histories are usually directed at specific issues of interest and can include questions regarding the use of dietary supplements, dieting history, food cravings, food aversions or allergies, and so on. They are generally self-administered and therefore easy and economical to use. There is a tendency to ask open-ended questions for hypothesis generation, but when closed questions are used, data analysis is much easier. Diet histories often serve as the basis on which dietary interventions are formulated.
2. Food records. These are prospective food diaries. Although they may be kept for varying lengths of time, a minimum of 7 days is viewed as generally representative of usual intake. Records of 3–4 days are popular and useful when at least one weekend day is included. To improve accuracy, food models, food weighing scales, and measuring cups may be used. Detailed instructions are essential. Continuous or periodic food records