Assessing food intake
Nutritionists usually analyze dietary intake data by converting the information on food intake into nutrient intake using relevant food composition databases. This approach simplifies the process of analysis and enables the resulting data to be compared with energy and nutrient requirements. Describing food intake in terms of foods rather than nutrients presents two practical difficulties that do not exist when food intake is analyzed in terms of nutrients. First, the variety of foods consumed is much greater than the range of nutrients for which food composi-tion data are available. Second, while essentially all individuals in a group contribute to nutrient intake data, not all individuals contribute food data for all foods, i.e., not all individuals are “consumers” of the same foods.
There are, however, several uses for which informa-tion on food intake is more relevant or for which information on food intake is needed in conjunction with data on nutrient intake. For example, food regu-latory authorities and agencies concerned with food safety and nutritional surveillance require data on the availability and intake of foods in addition to infor-mation on nutrient intake. Similarly, nutritional epi-demiologists are also interested in the relationship of different foods and dietary patterns with specific health outcomes.
The analysis and presentation of food intake data depends on the objectives of the study. When the purpose is to examine intakes of specific foods, intakes of foods may be expressed as means, medians, or frequency distributions of intakes, as the number or percentage of respondents consuming specific foods, or as the percentage contribution of food items to the total food intake, energy intake, or intake of nutrients of interest. Since not all members of a sample consume a given food, it is always important to indicate whether the total sample size or only the number of respon-dents consuming the food has been used in statistical calculations.
Although intakes of individual food items may be reported, food intake data are usually reduced to more manageable proportions by grouping foods into appropriate categories. While this can be done in different ways, for example in terms of composition, biological origin, or cultural use, the process is relatively straightforward within a given culture or country. It is more difficult, however, to develop a classification that can be used consistently across dif-ferent countries or food cultures. National food clas-sification systems tend to differ not only because the type and range of foods differs but also because the same foods are used in different ways. For the purpose of comparing food intake patterns between countries or regions, it is, therefore, necessary to develop a food classification or coding system that allows food data from individual regions or countries to be assigned in a consistent way.
The United Nations University Food and Nutrition Program for an International Network of Food Data Systems (INFOODS) was developed for the purpose of supporting work on the classification and naming conventions for individual foods and food groups.
Indirect information on food consumption, such as that provided by FAO food balance sheets and by data from household budget and similar surveys, is usually presented in terms of foods or food groups, but may also be converted to nutrients to provide information on the nutrient contribution of individ-ual foods or groups of foods.
Tracking changes in the food sources of nutrients and nonnutrients is particularly important in the context of technological developments in food pro-duction and manufacture that result in the addition of nutrients to foods, in the development of foods for specific functional purposes, and in the genetic modi-fication of foods. A specific example of the need for individual food, rather than nutrient, intake data is provided by exposure assessments to dietary non-nutrients such as food additives, pesticide residues, and other possible food contaminants.