Nutrient units of protein, vitamins and minerals – Nutrient Labeling

Nutrient units of protein, vitamins and minerals – Nutrient Labeling – A Tool for Nutrition Education, part 1

Jin-Zhou Liu

Proper nutrition requires that all the essential nutrients, i.e., proteins, lipids, carbohydrates, vitamins, minerals and water be consumed in adequate, but not excessive, amounts and in the appropriate proportions. It is essential for sustaining body processes, including normal organ development and function, reproduction, immune response, repair of body tissues, and in minimizing the risk of degenerative diseases. It is also necessary for sustaining activity level and working efficiency. Marginal or severe deficiencies may result from the inadequate or unbalanced intake of essential nutrients over varying periods of time. Although some specific nutrients are known to be more important than others in maintaining the functions of specific tissues, these nutrients are often dependent on the presence of other nutrients if they are to fulfill their unique roles effectively. As a result, nutritionists have an obligation to help the public attain and maintain an adequate and balanced intake of all the essential nutrients to meet their varying needs throughout life. The complexity of meeting this challenge mandates teaching the public to make effective use of information such as that to be made available at “point-of-purchase” under the provisions of the National Labeling and Education Act (NLEA) of 1990.

The Recommended Dietary Allowances RDAs) reflect the best current scientific judgment on the amount of each nutrient that is needed for maintenance of health. As such, they have become the standards for dietary guidance relevant to energy, protein, vitamin and mineral adequacy offered by nutrition scientists involved in nutrition education activities. RDAs also serve as the standard in evaluating the diets of groups and individuals. While it is not difficult for government, health agencies and nutrition professionals to use RDAs and information from food composition tables as a basis for developing public health nutrition programs, the layman has difficulty making individual food choices based on such a complex system involving many different units of measurement, such as milligram (mg), retinol equivalent (RE), international unit (I.U.), gram (g), kilocalorie (kcal) and standards which extend over quite different ranges. To make use of this information the public must first understand the concept of a balanced diet and the rationale for dietary standards. In order to select foods appropriate in kind and amount to assure nutrient adequacy they must learn to interpret and use the information provided on food labels derived from food composition tables and nutrient analyses provided by food processors.

This article proposes a simple and quantitative format for expressing the RDA relative to the information on the nutritional quality of foods to be provided through the FDA proposals for labeling of food products. In this approach the NRC’s Recommended Dietary Allowances (RDAs), the FDA’s proposed population-based standard intakes called Reference Daily Intakes (RDI) and the nutrient content of foods are all expressed in common units called nutrient units’ (NU). Under the original labeling system in which nutrient information was provided on only a limited number of foods, the consumer found it difficult to use the information to plan a balanced diet, or to glean sufficient information on the amount of a certain nutrient in many foods; they could, however, compare various sets of dietary alternatives from among labeled food products. Today, because of the imminent extension of mandatory nutrient labeling to the majority of foods in the U.S. food supply, it is now feasible to develop a system in which the lay public should be able to use this information to plan a nutritionally adequate diet. In principle, the approach proposed here is modelled after one advocated by Dr. Mary Swartz Rose, a pioneer in nutrition education in 1929-a time when our knowledge of essential nutrients and their requirements and information on nutrient quality of foods was available only to professionals.


With the high probability that nutrient information on food labels will be expressed as a percentage of the Reference Daily Intakes (RDI) for adults and children 4 or more years of age, we propose to use this same information as the standard for calculating the nutrient unit. The RDI is a population-weighted average of the RDAs for essential nutrients for adults and children 4 or more years of age. These standards are shown in Table 1. We define 1 nutrient unit as 1% of the standard value (RDI) for the nutrient. For example, since the RDI for protein is 50 g, 0.5 g of protein (1% of RDI) is 1 NU of protein. Similarly, 0.6 mg of vitamin C (1% of 60 mg) is 1 NU of vitamin C.

Table 1

The Reference Daily intakes

(RDI) Proposed by FDA as

Labeling Standards for Nutrients

Nutrient RDI(*)

Protein 50 g

Vitamin A 875 [mu]g RE

Vitamin D 6.5 [mu]g

Vitamin E 9.0 mg [alpha]-TE

Vitamin K 65 [mu]g

Vitamin C 60 mg

Thiamin 1.2 mg

Riboflavin 1.4 mg

Niacin 16 mg NE

Vitamin [B.sub.6] 1.5 mg

Folate 180 [mu]g

Vitamin [B.sub.12] 2 [Mu]

Calcium 900 mg

Phosphorus 900 mg

Magnesium 300 mg

Iron 12 mg

Zinc 13 mg

Iodine 150 [mu]g

Selenium 55 [mu]g

Energy 2350 kcal

(*) Each RDI here is equivalent to 100 NU.

The formula for calculating the number of NU in either a food or an RDA derived from this definition is as follows: Nutrient unit (NU)

= Amount of the nutrient/RDI for the nutrient x 100 From this it is obvious that reference daily intakes in NU for all nutrients for adults and children 4 or more years of age (excluding pregnant and lactating women), as defined by the FDA will be 1 00 NU. Similarly, the RDAs, when expressed in NU, will deviate only slightly from 100. In contrast, the RDAs are expressed in varied and often confusing units such as I.U. mg, [Mu]and kcal and in number of units, which may vary in magnitude from a fraction of 1 to several thousand.


The National Research Council’s RDAs for specific age and sex groups are then expressed in nutrient units with the RDIs serving as standards. These individual RDAs for different age and sex groups are converted to nutrient units by dividing the RDAs by RDIs, and then multiplying by 100. For example, the RDA for a particular age and sex group (e.g., iron for a 16-year-old female) is calculated as follows: NU (iron)

= RDA for iron (female 15-18 yr)/RDI for iron x 100

= (15/12) x 100 = 125 The NU equivalents of the RDAs for all age and sex groups are shown in Table 2.


The RDAs for most groups of people expressed in NU deviate only slightly from 100, depending on differences in age, sex and physiological conditions. The variations for protein RDAs expressed in NU form (shown in Fig. 1) indicate that recommended levels for most age and sex groups are close to the RDI (100 NU). The variations of the recommended dietary allowances of all nutrients for 25- to 50-year old men or women, expressed in NU form, are illustrated graphically in Figures 2 and 3, respectively.


By using NU equivalents for each of the 19 nutrients for which RDIs are available (protein, vitamin A, vitamin D, vitamin E, vitamin K, vitamin C, thiamin, riboflavin, niacin, vitamin [B.Sub.6, folate, vitamin [B.Sub.12], calcium, phosphorus, magnesium, iron, zinc, iodine, selenium) and energy the NU composition of any food can be calculated from information currently available in food composition tables. For example, the NU for calcium in 1 cup of milk becomes (288 mg/900 mg) X 100 = 33, or 33% of the RDI, the same information that appears on the label. Thus, the layperson can readily judge the nutrient quality of a food and have a sense as to the extent to which it meets his/her nutrient needs. Also comparison among various food sources of the same nutrient is facilitated. For example, the NU for 12 foods are shown in Table 3.



Because both the RDA for an individual and the nutrient content of a diet are expressed in the common unit (NU), the nutritional evaluation of diets can be easily completed by summing the NU of the food items eaten, and comparing the total to the recommended NU. For example, a 30-year-old woman consumed 1 oz of corn flakes and 1 cup of low fat milk (2%). The nutrients provided by this breakfast can be easily calculated. The contribution of some of the nutrients is shown graphically in Figure 4. From this simple addition, she knows that she gets 10 NU of energy, which is much lower than the nutrient units of protein, vitamin A, vitamin C, calcium and iron provided, making this combination a nutritious choice. She would then have information to help her select additional foods for the day that complement this breakfast choice. It would only be when the total NU for energy exceeded the NU for other nutrients that she would need to modify her choices to be sure she had a nutritionally adequate intake.


Since the proposed regulation of food labeling from FDA requires that the nutrient content be expressed as a percentage of the RDI, the NU of a food has the same value. Even when the percentage of the RDI is rounded as proposed, the labeled values will be so close to the NU that there is no need for concern about discrepancies. When the majority of all food products are labeled with NU or percentage of RDI, consumers can easily make a judgment about the nutritional quality of a meal or a diet by adding the NU of each item in the diet. Also, consumers can immediately know what percentage of their nutritional requirement they get from a single labeled food. To illustrate the kind of information the consumer would have available, Table 4 gives an example of the nutrient information that could be obtained from the label on one can of infant formula. Figure 5 is a graphic representation of the nutrient profile of a serving of a pizza expressed in NU.



Because of the availability on the food label of information on nutrients considered of major public health significance, and the marked increase in the number of foods which will be labeled, it will be possible for the public to utilize this information to either plan or assess the nutrient content of their diets relative to their requirements. The Nutrient Unit system proposed here allows an individual to monitor the extent to which the foods he/she selects contribute to meeting his/ her nutrient intake goal. The recommended daily intake for an individual is expressed as a number of nutrient units relative to RDI (these units are usually around 100). The message on the food label, which expresses the amount in food as a percentage of the RDI rounded according to prescribed rules, provides information which is essentially the nutrient units of various nutrients in the food. When these units are totalled for the diet, the intake can easily be compared to the recommended dietary allowances expressed in nutrient units for any one individual. This task is infinitely less complex than when a variety of units are used and when the magnitude of requirements for various nutrients is quite variable, e.g., 1.2 mg, 55 g, 800 RE, 2 mg, 2900 kcal. The relative similarity of values for recommended daily intakes and for nutrient composition of foods should simplify nutrition education efforts to maximize the use of nutritional information on food labels.

Figure 3 shows that for women all the recommended NU of nutrients except vitamin D and iron deviate by less than 10% from the RDI. In comparison, the U.S. RDA for various nutrients would have ranged from 100 to 133 NU, and recommended intakes would have deviated much more from the U.S. RDA than from the RDI. If a standard such as the U.S. RDA were used as an intake goal, it would be considerably more in excess than the recommended level in the National Research Council’s RDA.

The Nutritional Quality Index of Food (INQ) was proposed 20 years ago as a means of assessing the nutritional merits of a food. The INQ has the advantage of reflecting the nutrient density of a food, i.e., the extent to which the nutrient content of a food exceeds or is less than the contribution of this food to the energy requirement. This makes it a very valuable tool for assessing and comparing the nutritional merit of different foods. However, the INQ has limitations in assessing nutrient adequacy. First, the INQ cannot be used directly to calculate the total nutritional value of a diet composed of several kinds of food independent of calories; nor will the information on the label provide data on the INQ. In both instances additional calculations would be required, making it more difficult to get a rapid assessment of the nutritive value of a food or of total intake relative to requirements than with the NU system. Secondly, although the INQ indicates the relative amount of nutrient to energy in a food, consumers do not have information on the actual amount of calories and nutrients in a serving of food. The INQ cannot be used to make quantitative comparisons of nutrient content among different foods. This is because the INQ of each nutrient in each food is expressed relative to its own calorie content, which is generally different in different foods. Thus, an INQ of “1” for a particular nutrient does not mean the same in terms of actual nutritional value for different foods. Third, in contrast to NU, INQ itself cannot serve as the standard for diet evaluation because RDAs cannot be expressed in terms of INQ. The proposed nutrient unit system capitalizes on information as it appears on the label to afford a simplicity that allows consumers to overcome limitations of INQ for these uses.

In conclusion, the nutrient unit system qualitatively and quantitatively describes the nutritional values of foods and diets and makes it possible to use food composition data, RDA, and RDI at the same time. It is proposed that nutrient units can be used as a simple tool in nutrition education to facilitate the application of label information in selecting foods to meet nutritional needs. The use of label information to meet dietary guidelines regarding fat, fiber, sugar and sodium will be discussed in Part 11 of this series.


Department of Agriculture, Food Safety and Inspection Service. Nutrition labeling of meat and poultry products: proposed rules. Fed Reg 1991;56(229):60320-64. Department of Health and Human Services, Food and Drug Administration. Food labeling; general provisions; nutrient labeling; nutrient content claims; ingredient labeling; state and local requirements and exemptions: proposed rules. Fed Reg 1991;56(229):60366-891. Hansen RG, Wyse BW, Sorenson AW. Nutritional quality index of food. Westport, CT: AVI Publishing, 1979. National Research Council. Recommended Dietary Allowances, National Academy of Sciences. Washington DC, 1989. Pennington JA, Church HN. Food values of portions commonly used. 14th ed. New York: Harper & Row, 1985.

Jin-zhou Z. Liu completed the M.D. (1982) and Master of Science in human nutrition (1985) at Shandong Medical University and has taught nutrition at Shandong Medical University. His research has involved nutrition education for layman and more recently the impact of dietary garlic and selenium on cancer risk, He presently is a doctoral candidate in nutrition at Penn State University.

Dr. Guthrie is Professor of Nutrition Emeritus at Penn State University with a longstanding concern for communicating and interpreting nutrition science for the public.

Editor’s Note–part II of the series will deal with the use of label information in planning and assessing the use of macronutrients in the diet.

COPYRIGHT 1992 Lippincott/Williams & Wilkins

COPYRIGHT 2004 Gale Group