The usual aim of any dietary survey is to discover the habitual nutrient intakes of individuals. This article describes each of the dietary assessment methods available, together with their advantages and disadvantages.

There are several methods available:

Recording methods:

• Precise weighing method
• Weighed intake record (weighed inventory)
• Food diary

Recall methods:

• Diet history ('usual' intake)
• Diet recall (actual food intake), e.g. 24hr recall
• Food intake questionnaire, e.g. food frequency questionnaire

Each method has advantages and disadvantages and none is suitable in all circumstances. The choice of method is based on a number of factors:

• The purpose of the survey
• The foods and nutrients of interest
• The number of subjects to be surveyed
• The likely response rate
• Accuracy of the method
• Cost of the method per subject
• The age, sex and literacy of the subjects

Generally, the more accurate the method, the greater the cost per subject, the greater the degree of subject co-operation that is required and the lower the response rate. Thus when selecting a method, a compromise may have to be reached between a high response rate and the collection of precise dietary information.

If recording methods are used, it is generally agreed that seven days is sufficient. Occasionally, periods of three days (two weekdays plus one weekend day) or four days (two weekdays plus two weekend days) have been used, since calculated nutrient intakes from these records have been shown to be similar to those from seven day records. At least one weekend day must be included in the survey because nutrient intakes of weekend days may differ greatly from those of weekdays.

Reference:
Fehily A. Dietary assessment. In: Manual of Dietetic Practice, Fourth Edition. (Eds B Thomas and J Bishop). Oxford: Blackwell Scientific Publications, 2007, p.32-40.