| Food Composition Data: A User's Perspective (1987) |
|Managing food composition data|
|Maintaining a food composition data base for multiple research studies: the NCC food table|
Minimizing redundancy in the nutrient data base
Ongoing maintenance and expansion of a nutrient data base to include increasing numbers of nutrients and other food components can be efficiently accomplished only if the number of entries requiring routine maintenance can be kept to a minimum without losing the specificity required by the many users of the system.
All entries in the NCC Food Table are either elemental or composite entries. Elemental entries may be defined as entries for which nutrient values are maintained in the Food Table. Composite entries are defined by an ingredient list of two or more elemental entries with specified amounts. Nutrient values for composite entries are calculated from the ingredient list by the computer. This system limits the routine maintenance of the Food Table to the elemental entries.
The following guidelines have been developed by the NCC to minimize redundancy in the Food Table by limiting the number of elemental entries.
1. Include Foods Only in the Forms in Which They Are Eaten
Since analysis of the dietary intake of individuals living in the United States and Canada is the common need of all current users of the NCC system, the Food Table need not include foods in forms in which they are never consumed by the study populations. Thus, no entries are included for most raw meats, uncooked pasta, or certain raw vegetables such as potatoes. Many foods commonly eaten in other countries do not appear in the NCC Food Table because they have not been encountered frequently enough on the dietary records received at the NCC. As various ethnic foods increase in popularity in this country, it is expected that more foreign foods will be added to the Food Table. Sushi is an example of a recent addition to the NCC Food Table.
For composite entries of cooked recipes, cooked ingredients are substituted for the raw ingredients whenever possible. For example, if a casserole is made with raw rice, the corresponding amount of cooked rice is entered as a recipe ingredient in the composite entry. Use of the nutrient values of cooked rather than raw ingredients makes the calculated nutrient content more similar to the actual nutrient content of the food as eaten. This system also reduces the number of elemental entries required in the Food Table by eliminating the need to maintain raw food entries as recipe ingredients for composite entries.
2. Combine Foods of Similar Nutrient Content into a Single Entry
When similar foods differ by less than the established limit values for each nutrient, the foods are grouped together in a single entry. For example, spinach cooked from fresh and cooked from frozen are combined in a single entry. If at some point a new nutrient or other food component is added to the Food Table for which the value in cooked fresh spinach differs from that in cooked frozen spinach by more than its established limit value, the two items would be given separate entries.
3. Add New Foods as Composite Entries Rather than as Elemental Entries Whenever Possible
Even though some mixed dishes have been analysed for nutrients in the composite state, it is preferable to add them to the Food Table as composite entries rather than as elemental entries as long as the amounts of ingredients can be specified and the calculated nutrient values closely match the values provided for the composite item. Most home-prepared foods in the NCC Food Table are maintained as composite entries. Some commercial products with well-defined ingredients are also entered into the Food Table as composite entries. Approximately one-third of the current NCC Food Table consists of composite entries.
4. Use of Prep Codes and Fat Codes
"Prep codes" to specify amounts of fat added in various food preparation methods and "fat codes" to designate the type of fat used are other procedures used by the NCC to limit the number of elemental entries. These procedures have been described in detail elsewhere . Prep codes prompt the appropriate computer algorithms to calculate the amount of fat, salt, or other additions for various food preparation methods of a basic food. Thus a single entry can be used for many different preparations of that item. For example, a piece of light-meat chicken without skin can be breaded and fried in corn oil, baked with butter, or broiled without added fat by invoking the appropriate prep codes and fat codes with the same elemental item.
5. Use of Add-Principal-Fat (APF) Recipes
Foods that contain significant ingredient or cooking fats are designated as APF recipes and are maintained in the NCC Food Table as composite entries. French fried potatoes, pie crust, and salad dressing are examples. All APF recipes require specification of the type or brand of the predominant fat ingredient. Thus, the nutrients in corn bread could be calculated using bacon fat, soybean oil, shortening, or any other appropriate fat. This system allows considerable flexibility for specifying ingredient and cooking fats without increasing the number of entries in the Food Table.
6. Use of Coding Guides for Brand-name Products and Food Characteristics
Coding guides are alphabetical indices of specific types, classes, or brands of foods that designate the particular NCC Food Table entries into which they are classified. For example, the Brand Name Margarine Guide specifies which of the approximately 60 margarine entries in the Food Table should be used for each of approximately 400 brand-name margarines. The Beef Guide specifies which Food Table entry should be used for each type or cut of beef. The current NCC system includes approximately 80 guides. Each guide also includes directions for coding items when the type or brand is not specified.
7. Handling of "Uncodables"
When an item appearing on a dietary intake record cannot be coded according to established procedures, the item is documented on an Uncodable Form to be resolved by the nutrition staff. If the uncodable item is a new product on the market, ingredient and nutrient information is requested from the manufacturer to determine proper coding. If the uncodable item is a composite food consisting of unknown amounts of ingredients, the nutritionist makes a judgement on proportions. Decisions on the coding of uncodable items are stored in a crossreferenced file to facilitate standardization for future coding decisions. Uncodables that begin to appear frequently on intake records are added to the Food Table as new entries. An example of an uncodable recently converted to a new entry is trail mix. The uncodables system prevents the unwieldy expansion of the Food Table that would result from the inclusion of many infrequently consumed items.
Use of the various procedures outlined above effectively limits the number of elemental entries in the NCC Food Table. Thus, updating can be routinely implemented and new nutrients added with minimum effort while maintaining maximum flexibility for detailed specificity to meet user needs.