| Food Composition Data: A User's Perspective (1987) |
|The uses of food composition data|
|Epidemiological uses of food composition data in the European context|
Suggestions for improvement
Since the use of food composition tables in nutritional epidemiology concerns mainly estimation of the composition of food consumed by individuals, it makes sense to regard the entire process as closely interrelated- the dietary assessment, food coding, and referencing of tables. Some of the problems beginning with the assessment of dietary behaviour are: (1) non-standardized methodology; (2) portion size estimation; (3) translation; (4) mixed dishes; (5) different food codes; (6) different food grouping systems; (7) differences in food tables; (8) food compositional differences; (9) missing values; and (10) definitions of edible parts.
In many cases only minimal effort would be required to improve and simplify nutritional analysis in international epidemiological studies. The components of food-nutrient data-base systems (data files and programs) are compartmentalized and presented diagramatically in figure 2, emphasizing the individual areas needing enhanced development as well as their interdependence. The numbers in the diagram link relevant system components to numbered suggestions in the following text.
1. Standardized Dietary Assessment Methods
Although basically common terminology is used in dietary assessment, the procedures followed are non-standardized and seldom described or documented. A 24-hour recall for one person may be a computer-based decision tree , for another it might be an empty piece of paper, a pencil, and a simple question on the subject "Please write down what you ate yesterday." Handbooks on standardized procedures for different dietary assessment methods would improve the situation.
2. Standardized Portion Sizes
All subjects have difficulties in estimating the exact portion sizes of foods consumed (particularly retrospectively), requiring estimations and assumptions to be made by the interviewer or coder. The difference between weight of purchased product (often known) and that of actual item consumed (without bone, pits, skin, with water, etc.) are all part of this issue. The use of standardized portion sizes for individual foods within countries could help. The application of standard weights and density measures where applicable, as well as common models for small, medium, and large portions, cuts of meat, portions of grains, noodles, and baked products, would be useful. A standard set of food models for use in dietary assessment could be a step in the right direction.
Table 1. Native-language food-table entries for apples, butter, beer, and beef
|Danish||Æle||Smør||Øl||Oksekød, højrebsfilet, afpudset, ra|
|Spanish||Manzana||Mantequilla||Cerveza||Came, semigrasa (vacuno)|
|Dutch||Appel||Boter||Bier||Rundvless, gemiddeld, vet onbereid|
|Italian||Mela||Burro||Birra||Bovino adulto semigrassa|
|Greek||Mila||Boutyro||Bira||Bodino, apexes mbriz omes|
|Swedish||Apple||Smör||Maltdryck||Not biff dubber|
3. Names and Translations
The difficulty of translating foods from one language to another cannot be underestimated. Even within a country, colloquial food names are inexact and can be misleading. Table 1 gives a comparison of the differences between countries in the names of simple foods in food tables. Here apples, butter, beer, and beef, as entered in the food tables of IO countries, are compared. Apples and butter between countries are somewhat comparable. Beer, however, brings in the complication of different products with different formulations and alcohol content. And beef is even more troublesome, as different countries have different standards for cutting and names for the various cuts, different fat contents and extent of trimming. A considerable part of an international coding workshop held in Heidelberg in February 1985 was devoted to the description of food items. (Unpublished proceedings available from the author.) Table 2 presents a list of many of the published food nutrient tables currently available in Europe. To use these tables one needs not only a good translation of the food items and measured parameters, but also an understanding of the language to read the introduction in which critical information on using the tables is found. A common pitfall in translating foods is in situations where an identical or similar food name is used in two countries but an entirely different product is meant. Another problem is that of foods whose names convey little meaning as to content, such as those found in table 3.
4. Mixed Dishes
People often eat dishes that are prepared elsewhere and the identity of whose ingredients remains unknown to them. Salads, stews, soups, cakes, casseroles - the list of foods in which one cannot determine what has been added just by looking is practically endless. Mixed dishes in general present problems, as hundreds of different recipe variations are involved for each dish of a given name. They are such an important part of European diets, however, that they cannot be ignored. A simple example is pizza, which is known everywhere by this name but is prepared in a myriad of ways - in some areas it is made without tomatoes, in others without cheese, and when cheese is used sometimes it is mozarella, sometimes Gouda, sometimes emmentaler. Standard recipes would at least prevent arbitrary differences and allow for calculations on a common basis when exact information is not available.
Table 2. Major European food tables
|Federal Republic of Germany||1982/83||Souci, Fachmann, Kraut|
|1980||Ostrowski and Josse|
|Italy||1981||Fidanza and Versiglioni|
|1983||Carnovale and Muccio|
|Norway||1977||Landsforeningen for Kosthold og Helse|
|Poland||1978||Berger et al.|
|Portugal||1977||Gonzales-Ferreira, da Silva Graza|
|Spain||1983||Andujar Anas, Moreiras-Verela, Extremara|
|United Kingdom||1978/85||Paul and Southgate|
Table 3. Some mixed dishes translated into English
|Netherlands (Dutch)||Children's happy biscuits|
|Denmark (Danish)||Italian salad|
|United Kingdom (English)||Welsh rarebit|
|Federal Republic of Germany (German)||Lady's finger|
|Finland (Finnish)||Jansson's temptation|
|Italy (Italian)||Cake Margherita|
|Poland (Polish)||Bird milk with lemon|
|Popular hunter stew|
|Sweden (Swedish)||Pyramid cake|
Despite the fact that the large proportion of the European diet comes from mixed dishes, relatively few prepared dishes have been analysed and presented in composition tables . There are different methods for imputing the nutrient values of food that have undergone various preservation and preparation processes, none of which has been shown to be the most accurate . Recommended procedures for imputing values would at least enhance the comparability of results.
5. A Standard Code
Different coding systems with different orientations, different groupings of food, and different levels of specificity  stand in the way of data exchange, comparison of results, and recalculation of surveys based on foreign tables. A common coding system would allow comparisons between studies of the frequencies and amounts of individual foods consumed. Also, it would help bypass the translational problems in identification of the same and similar foods. It would also simplify the application of common grouping schemes for foods.
6. Basic Food Groups
The problem of grouping foods and products has been addressed earlier. Since tens of thousands of food items are consumed in Western populations, it is necessary to aggregate individual foods into groups for further analyses. Brand-name items usually fall together, but egg dishes, vegetable casseroles, and stews are foods that typically differ from one grouping scheme to another. Different schemes for grouping foods can lead to antifactual differences or false conclusions regarding epidemiologic associations. Agreement on at least the major food groups and guidelines for alternate grouping schemes would be useful.
7. Food-table Format
Differences between different food tables are apparent as soon as one opens two different tables. The format with which foods and nutrients are listed differs, some tables have one food per page, others lists of foods and lists of nutrients. The ordering of the nutrients differs, as do the units of measure, the exactness, and the number of significant digits. There are also differences in the factors used for calculation . Again, the need for a standardized format is demonstrated here (see chap. 10).
8. Food-nutrient Differences
The nutrient composition of an apple or potato in the FRG is not likely to be the same as in Holland, and is even less likely to be the same as in Sweden or in Spain. First of all, different species are used; second, different amounts of sunshine influence the nutrient level; third, the trace elements are strongly influenced by the soil. The breadth of variation may be as great within a country as between countries. The fat content of similar foods differs tremendously from country to country. Little can be done here in general, but this problem discourages the exchange of data, particularly important when large amounts of the products are being exchanged within the European Common Market or eaten on vacation outside the country. Data exchange requires some means for the user to find the proper food in a language he can understand (source and sampling information) and a presentation of the values whose analytical method and accuracy are available to him. Since variability of values within a table can be considerable, information is needed to enable the end-user to know the laboratory intra-sample variation and variation between species, as well as the origin of the food sampled and the time of analysis.
9. Missing Values
There are many types of missing values in nutrient tables. As Greenfield and Southgate have pointed out, there are imputed values, borrowed values, values calculated from a measured factor, values that are available for many foods but not available for others (absent), and nutrients that are not included at all . For the epidemiologist the values which are labelled missing bring further analyses to a halt. Zeros in the analyses make the determination of a gradient of risk impossible - an estimation is almost always preferable. Greater exchange of nutrient information between countries would allow for the eradication of many of the missing values in tables. Efforts to correlate information on nutrient losses and gains in preparation of foods would help improve the quality of estimation of nutrient contents in preferred foods which have not been analysed.
10. Edible Parts
So-called "edible parts" of foods can differ from culture to culture. The French for example consume only the soft inner portion of Camembert cheese. Germans eat the crust as well, and would not expect this to be missing in the nutrient analyses. Descriptions of the food sample analysed would help prevent misuse of foreign data.
This list of possible problems with food composition data is not exhaustive. Additional suggestions for improvement would include increased availability of data  in machinereadable form and a solution for updating data more easily and less expensively.