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close this book Food Composition Data: A User's Perspective (1987)
close this folder Other considerations
close this folder A system for evaluating the quality of published nutrient data: Selenium, a test case
View the document (introductory text)
View the document Introduction
View the document Background
View the document Procedure
View the document Criteria
View the document Calculation of the mean SE value and confidence code
View the document Results
View the document Discussion
View the document Implications
View the document Acknowledgements
View the document Disclaimer
View the document References

Introduction

Introduction

Food composition data are used by nutritionists, dietitians, and epidemiologists to assess the adequacy of the diets of population groups, subgroups, and individuals. They are used to determine federal and state government policy regarding food and nutrition programmes and other public health efforts. Data relative to the assessment of nutrients and contaminants such as pesticides are used to formulate the policies of regulatory agencies such as the Food and Drug Administration (FDA). In addition, the food industry uses food composition data to assist in food labelling, quality assurance, and product development. Ideally, data to be used for such varied and far reaching assessment and policy formulation should be accurate and precise by analytical standards, and should represent both the qualitative and quantitative standards and the qualitative and quantitative distribution of nutrients or other components found in the food supply consumed by the group or individuals to be studied. Because data obtained in such a manner that they meet all of these requirements are scarce, critical evaluations of the limitations of available published data are needed.

Food composition data of variable quality and quantity can be collected from many different sources. They can be obtained from manufacturers of food products; these may include individual values for replicates or mean values for specific samples. Data can be taken from product labels. Certain data are obtained directly from the analysis of foods purchased and sampled specifically for the purpose of determining their composition. These studies may or may not be published. Food composition data may also be gathered from the scientific literature as the indirect results of the development of analytical methodology, animal feeding trials, soil treatment trials, and bioavailability studies. While these published studies may accomplish stated objectives, not all the data may be suitable for use in food composition tables and data banks. Since the requirements of data users can be diverse, the suitability of specific data for inclusion in a data base should be evaluated according to objective criteria that are known to users of the data. Some indicator of data quality is necessary for each nutrient in each food to provide the data user with a measure of the reliability and usefulness of specific values in the data base.

The main objective of this work was to develop a set of criteria that could be applied to published analytical data (a subset of available nutrient data) for any specific nutrient or component in foods. Selenium (Se) was selected as a test case for these criteria because of the current high level of interest in this nutrient and the need for accurate assessment of Se intake in a number of ongoing human studies. Furthermore, published Se data have been generated by a limited number of satisfactory analytical methods and constitute a finite data set suitable for testing such a system of criteria.

A secondary objective was to provide analysts with a set of guidelines for designing nutrient composition studies and reporting their results. Such guidelines can also be used by journal editors and their reviewers to evaluate scientific papers submitted for publication and to elicit details of a study important to compilers of nutrient composition data.

Criteria developed specifically for Se were applied to the body of Se data available in the scientific literature. Ratings determined in the process were combined to yield a confidence code (CC) for the mean Se value of each food item reviewed. This paper will describe these criteria and their application, and give several examples. (A table of foods with their Se concentrations, respective CCs, and specific references will be published separately.)