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4. Assigning the correct food component tagnames to the nutrient data

Introduction
Alcohol
Amino acids: total essential amino acids
Amino acids: essential to total amino acid ratio
Amino acids
Carbohydrate
Carbohydrates and monosaccharide equivalents
Cholesterol
Energy
Fat
Fatty acids
Fibre
Folate
Glycerides
Iron
Niacin
Nitrogen
Protein
Selenium
Starch
Sugar
Vitamin A
Vitamin B-6
Vitamin C
Vitamin D
Vitamin E

Introduction

Nutrient names used to label data values in food composition tables are sometimes not sufficient to identify precisely what those data actually represent. For example, do the "niacin" values in a specific food table represent only nicotinic acid, or do they include the quantity of nicotinamide in the foods? Do they represent only preformed niacin, or do they include the niacin equivalents from tryptophan?

In order to eliminate the ambiguity inherent in some of the commonly used food component names, INFOODS tagnames have been created for identifying food component data values. When necessary, multiple tagnames were created which correspond to one common nutrient name. Three situations have required the creation of multiple tagnames: (1) to identify values for the individual active components of a nutrient, (2) to specify the method used for determining a nutrient value, and (3) to distinguish between the terms in which the values may be expressed. As a result, some consideration may be required to determine exactly what a particular data value represents before a specific tagname can be assigned. Those food components that are likely to pose the most difficulty for tagname assignment are discussed below.

Alcohol

"Alcohol" values in food composition usually refer to ethyl alcohol (ethanol). These values should be assigned tagname <ALC>. Occasionally, values for methyl alcohol appear in food composition tables, and should be identified with the tagname <METH >.

Amino acids: total essential amino acids

Different definitions exist for which amino acids should be included in total essential amino acid values. Some definitions include only the eight amino acids that cannot be synthesized in the human body: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Other definitions also include arginine and histidine because they are essential for infants, or cystine and tyrosine because of their sparing effects on the dietary requirements for methionine and phenylalanine. The tagnames for total essential amino acid values specify which amino acids were included in the total. Tagnames are also available to identify values for which it is unknown which amino acids were included in the total.

The total essential amino acid tagnames also distinguish whether the value is expressed per quantity of edible portion of food, per quantity of nitrogen in the food, or per quantity of protein in the food. The tagnames for values expressed per quantity of edible portion of food are subsidiary to the <comp> structural tag, while the tagnames for values expressed per quantity of nitrogen or protein are subsidiary to the < drvd-comp > structural tag.

All tagnames that can be assigned to total essential amino acid values are listed below with their respective structural tags.

Amino acids: essential to total amino acid ratio

In order to assign an appropriate tagname to values for the essential to total amino acid ratio, one must consider which amino acids were included in the total essential amino acid value in the numerator of this ratio. (See the preceding section for the various definitions of which amino acids are considered to be essential.) The available tagnames are listed below. A similar problem arises with the denominator of these ratios. The exact list of amino acids that are included in the "total" varies from table to table, usually simply comprising the sum of whatever amino acids were measured and reported on for that particular table. Consequently, these values may not be exactly comparable from table to table. Therefore, all of them have been assigned tagnames ending in hyphens. When a clear standard emerges for the denominator, more specific tagnames will be assigned. All are subsidiary to the <drvd-comp> structural tag.

Amino acids

For amino acid values, tagnames are assigned which identify whether the values are expressed per quantity of edible portion of food, per quantity of nitrogen in the food, or per quantity of protein in the food. The tagnames for values expressed per quantity of edible portion of food are subsidiary to the <comp> structural tag, while the tagnames for values expressed per quantity of nitrogen or protein are subsidiary to the <drvd-comp> structural tag. All amino acid tagnames are listed below with their respective structural tags.

Carbohydrate

Values labelled "carbohydrate" in different food composition tables may actually represent different components of the carbohydrate content. A major difference is that some carbohydrate values represent only available carbohydrate, while others represent total (available plus unavailable) carbohydrate. As a finer distinction. available carbohydrate values may be expressed as a quantity of carbohydrate or in terms of monosaccharide equivalents, and total carbohydrate may be calculated by difference or by summation. The specific tagnames for identifying carbohydrate values are listed below. Included is a tagname that can be assigned to carbohydrate values when it is not known which of the specific carbohydrate tagnames is appropriate for the data. All tagnames are subsidiary to the <comp> structural tag.

Carbohydrates and monosaccharide equivalents

A carbohydrate value may be expressed as a quantity of carbohydrate or as a quantity of its monosaccharide equivalent. Therefore, there are two possible tagnames corresponding to these two modes of expression for identifying each carbohydrate or carbohydrate component value. These carbohydrate tagnames are listed below. All are subsidiary to the <comp> structural tag.

Cholesterol

Values for the quantity of cholesterol in a food may differ depending on the method used for analysis. Therefore, cholesterol tagnames have been created which are method-dependent. These tagnames are listed below, along with a tagname that can be assigned to cholesterol values when the method of determination is not known. AH of these tagnames are subsidiary to the <comp> structural tag.

Energy

Values representing the energy content of a food may differ depending on whether the energy was determined by direct analysis of the food or whether it was calculated from the energyproducing components using appropriate conversion factors. Therefore, energy tagnames have been created which are method-dependent. These tagnames are listed below, along with a tagname that can be assigned to energy values when the method of determination is not known. AH of these tagnames are subsidiary to the < comp > structural tag.

Fat

Values for the quantity of total fat in a food may differ depending on the methods used to determine the values. Values derived by analysis using continuous extraction have been found to be consistently different from values derived using other methods. Therefore, two tagnames for total fat values have been created to specify this difference. These tagnames, listed below, are subsidiary to the <comp> structural tag.

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