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The state of food composition data: an overview with some suggestions

Kent K. Stewart
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA

One of the cornerstones of an effective and useful INFOODS system is the availability of good quality food composition data. This paper attempts to make an evaluation of the current status of food composition data, to suggest appropriate goals for food composition data, and to suggest a set of strategies to accomplish these goals. Its purpose is to begin to establish some of the broad concepts and principles essential to development of a high-quality food composition data base. While most of my examples are taken from experiences in the United States, these comments have general applicability in the rest of the world.

GENERAL COMMENTS

Almost all current composition data bases are designed to provide values that are representative of the "normal" level of the compound found in that food. These data are meant to be used as the recommended dietary allowances are meant to be used for recommended nutrient intake, i.e., for the evaluation of the aggregate of the system. The use of data base values may well be inappropriate for the evaluation of individual situations. With the current available data systems, if individual values are needed for any reason, the best recourse may be to make the determination of the level of that compound in the specific lot under consideration.

It is unrealistic, at this time, to expect that any public food composition data base system will provide precise data on all the components of any individual food item. The exact concentrations of food components are subject to too many variables to be completely predictable. Other than individual assay of each lot for each food component (a very expensive undertaking), the best one can hope for is the range and precision of the measurements and some estimation of the quality of the data. The responses to dietary intake rarely manifest themselves from the ingestion of a single food, a single meal, a single day's diet, or even a single week's diet. Most often the problems are the cumulative results of long-term consumption. Quite often the responses are complex and are the result of the interactions of several dietary components with the phenotypic response of the consumer. These conditions have profound implications for the development of food data base systems.

PRIVATE VERSUS PUBLIC DATA

In the discussion of the composition of foods, care must be taken to distinguish between public (government, university) and private (industry) data. Because of the great sensitivity of the issues surrounding dietary intake, there are many sources of data that are, and will remain, excluded from the public eye. The public versions of these data will often reflect policy actions of the generating agency as much as the actual scientific aspects of the collected data. It is extremely unlikely that these problems associated with private versus public data will be easily overcome. The very issues that generate the need for data bases generate the sensitivity of the data. The user of data bases must be aware of these problems and understand the limitations of public data base systems.

CURRENT STATE OF KNOWLEDGE

Given these reservations, what is the current state of public knowledge on the composition of foods?

Nutrient data. The current state of our knowledge of the nutrient composition of foods has been reviewed a number of times. The recent evaluation of the Nutrient Data Research Branch of the Human Nutrition Information Service of the US Department of Agriculture is shown in tables 1 to 5. Probably the condition of the data base in the United States is similar to that found in some of the other high-quality data bases, and is most likely an example of the best that is available.

These tables show that, for most commodity items, there is a reasonable amount of data for the commonly mentioned nutrients. However, much less information is available for processed foods. The lack of data for certain nutrients is quite noticeable and often reflects the lack of reliable methodology for the nutrient assay. There have been a number of recent assessments of the state of the methodology for the determination of nutrients in foods. Table 6, from a recent talk by G.R. Beecher, gives the current assessment of methods as seen by the scientists at the USDA Nutrient Composition Laboratory in Beltsville, Maryland. There are a striking number of nutrients for which the methods are ranked as neither adequate nor substantial. It is difficult to believe that much good data are available for these nutrients.

The data in private data systems are probably better, particularly for those nutrients whose contents appear on the labels of processed foods. One would expect that there are hundreds of values in the files of the laboratories monitoring the nutrient content of foods. These individual values, in sum, should give excellent estimates of the mean, standard deviation, and ranges of nutrients for individual food items. However, the high quality private nutrient data are most likely limited to those nutrients for which the AOAC methods give reliable results. Few food laboratories have the personnel or funding to do independent method development, and the legal constraints on the processors make it quite unlikely that non-AOAC methods would be used for routine product assay. The release of private data has, to date, been restricted, and is sometimes limited to the label values themselves. In the United States (and perhaps in other countries), label values present the processor with several legal and commercial dilemmas, and the values released are often as much a matter of corporate policy as they are of scientific study.

Non-nutrient data. Many of the demands for food composition data are based on the belief that the intakes of various non-nutrient components are directly or indirectly related to the ills of mankind. Concern with the ingestion of carcinogens is an obvious example. These compounds can be classified as (i) naturally occurring non-nutrients and/or toxicants, (ii) food ingredients, and (iii) inadvertent additives and/or contaminants. (There is another class of compounds that is often of concern, food borne infectious agents; however, the nature of these agents is such that they are not suitable for inclusion in food composition data banks and I will not discuss them further in this paper). The nature of each of the three classes is such that it is appropriate to discuss them separately.

NATURALLY OCCURRING NON-NUTRIENTS AND/OR TOXICANTS

A large number of non-nutrient compounds occur naturally in foods; some have been demonstrated to have a variety of detrimental effects. Most professionals in food science and nutrition know of the enzyme inhibitors, goitrogens, lathyrogens, haemagglutinins, etc. that occur in plant and animal tissues. A considerable amount is known about the biochemistry and chemistry of these compounds. However, there is very little composition information suitable for food data bases. There does not seem to be very much information on the normal effects of processing on these compounds, although there seems to be a general impression that thermal processing markedly decreases their activity. Except for a few specialized cases, such as the tetraodontoxin from puffer fish, and some food-borne allergens, there do not appear to be many general public health problems associated with these naturally occurring compounds. Whether they have more subtle effects is generally not known. The development of a data base for food borne allergens would probably be of considerable use; but to my knowledge, not much information exists in data banks at this time.

FOOD INGREDIENTS

Most processed foods are made from one or more basic foodstuffs and a number of chemicals are added to improve the quality of the product. Those compounds that have been intentionally added to the basic foodstuff have been called "intentional food additives" and have been discussed in two publications of the US Food and Nutrition Board 11, 2). At present, data are available for about 500 additives. Overall, the data are rather general in nature; little more is available than the approximate maximum and average levels found in different foods. Typical descriptors for foods are words such as "candy," "beverages," and "spices."

Much more information is probably available on a private basis. Most food companies are likely to at least know how much of the additive was originally added to the product, even if they may not know the effect of processing on the final level. I suspect that, in most cases, few analytical data exist on the levels of these compounds in the final processed product prepared for eating. There are obviously some data that are suitable for food composition data bases for these compounds. However, in general, the quality of the data is probably much poorer than that in the nutrient composition data bases.

There is another class of food ingredients whose levels are predictable: (i) compounds that occur in the food as the result of the chemical transformations occurring during processing, storage, or in the final preparation of the food for consumption; and (ii) those compounds that are formed as secondary reaction products in the manufacture of food ingredients and food packaging materials that are transmitted into the foodstuffs. The nitrosamines are well known examples. Many other such compounds undoubtedly exist. Relatively few composition data for these compounds are available. In most cases, these technical data will be difficult to acquire, because the numbers, kinds, and levels of these compounds are as dependent upon the process as upon the recipe. While some of the additions were not intentional, the final levels are predictable (at least in theory). This is not necessarily the case for the next class of compounds.

TABLE 1. State of Knowledge of Nutrition Composition-Carbohydrates

Source:
Nutrient Data Research Branch Consumer Nutrition Division Human Nutrition Information Service
US Department of Agriculture Hyattsville, Maryland 20782 January 1983

Key:

TABLE 2. State of Knowledge of Nutrient Composition-Lipids

Source: Nutrient Data Research Branch Consumer Nutrition Division Human Nutrition Information Service US Department of Agriculture Hyattsville, Maryland 20782 January 1983

Key:

TABLE 3. State of Knowledge of Nutrition Composition-Minerals

TABLE 4. State of Knowledge of Nutrition Composition-Protein and Amino Acids

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