inaccurate results for a variety of reasons. For some nutrients (and other food components of interest), accurate procedures may not be available. For example, the usual procedures for analyzing the folate content of foods are known to underestimate the actual levels, and thus estimates of folate intakes are likely to be low. Both the extraction procedures and the enzyme digestion treatments may be less than optimal for food folate, and although recent procedures solve some of these problems, folate values on most food composition tables are probably underestimated. Dietary fiber in foods provides another example of possibly incorrect methods. Many older food composition tables contain a variable named fiber, but the values are for crude fiber. Crude fiber is measured using procedures that destroy some of the physiologically important fibers, and thus it is an underestimate of the true dietary fiber content. Recent methods measure either total dietary fiber (defined as all fibers that are not digested in the human gut, including lignans) or nonstarch polysaccharides (excluding lignans).

Inaccurate analyses may also occur when access to the best laboratory equipment is not available, either because the costs are too high or because the technical expertise to use the equipment is not available. For many of the antioxidant compounds, such as carotenoids and tocopherols, quantification by mass spectrometry (MS) yields the most sensitive detection limits, although analysis using high-performance liquid chromatography (HPLC) is adequate in most cases. However, because the equipment, maintenance, and reagents are often too expensive, laboratories (particularly in developing countries) may use older methods, such as spectrophotometry combined with open-column chromatography. Nutrient values derived using such methods are less accurate than those resulting from HPLC and MS methods.

Users of food composition tables should ask when and how analytic values were obtained. Likewise, compilers of these tables should clearly document the analytic procedures used to obtain all values and ensure that such information is readily available to users.

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