enough to use to assess the adequacy of dietary intakes of either individuals or groups due to several limiting characteristics of semiquantitative food frequencies.
First, there is no direct quantitative assessment of individual amounts consumed (Kohlmeier and Bellach, 1995). Either an average portion for all individuals in a group is assumed or the options are limited to a few categories, such as small, medium, and large. Assessment requires a precise quantification of nutrient intakes, and for this, accurate portion sizes are needed. Frequencies of consumption are truncated in a limited number of categories (usually five or seven).
Second, a food-frequency questionnaire does not assess intakes of all available foods. Foods are limited to those that are considered major contributors to the nutrients under study (Block et al., 1986), or to the foods that contributed most to the variance in intake in a specific group at the time the questionnaire was designed (Willett et al., 1987). Food-frequency questionnaires do not attempt to capture all food sources of a nutrient quantitatively.
Third, because of the discrepancy between thousands of foods being offered in a supermarket and a set of questions limited to a few hundred at most, many foods are combined in one question. Food composition data are averaged in some way across these foods, and the individual who consumes only one or another of these or eats these in other proportions will be incorrectly assessed with the nutrient database being used. As a result intakes may be either over-or underestimated. Also often overlooked is that food-frequency questionnaires are only applicable to the population for which they are designed and are based on their consumption patterns at a specific time. Continually changing food consumption patterns and new food offerings require that periodic changes be made in food-frequency questionnaires.
Diet histories, like food frequencies, attempt to capture usual diet but, unlike food frequencies, include quantitative assessment of portions and include the assessment of all foods eaten in a cognitively supportive fashion (meal by meal) (Burke, 1947). Because they are quantitative and do not truncate information on frequency, amount, or the actual food items consumed, diet histories overcome many of the limitations of food-frequency questionnaires for assessment of the total nutrient intakes of individuals (Kohlmeier and Bellach, 1995). Diet histories have also been shown to capture total energy intake more accurately than other methods (Black et al., 1993). However, if conducted by an interviewer, rather than a preset com-