| Food Composition Data: A User's Perspective (1987) |
|The uses of food composition data|
|Food composition -a key to dietary appraisal and improvement in the United States|
Food composition data needs
National nutrition monitoring system
Approaches to meeting data needs
BElTY B. PETERKIN
Human Nutrition Information Service, US Department of Agriculture, Washington, D.C., USA
The US Department of Agriculture (USDA) has traditionally been the primary provider of food composition data in the United States. Food composition data are vital to the major responsibilities of the Department: (a) to ensure that an adequate, wholesome, and nutritious supply of food is available and (b) to provide information to help Americans select good diets . USDA food composition data are also used extensively by the Department of Health and Human Services (DHHS) - the agency with responsibility for studies of diet and disease and for the nutrition-labelling programme.
USDA contributes to food and agricultural progress throughout the world. This activity and its role as the provider of US food composition data explain USDA's support of INFOODS and earlier efforts to help make food composition data available in various regions of the world.
A wide range of activities helps to fulfil USDA's mission as it relates to nutrition. Research, information, education, regulatory, and food assistance programmes are examples . Each requires food composition data. This paper describes some of these activities and their food composition data needs, and outlines the means by which USDA's Human Nutrition Information Service (HNIS) attempts to meet these needs (see chap. 11).
Food composition data needs
Human Nutrition Requirements Research
USDA's Agricultural Research Service (ARS), in its five Human Nutrition Research Centers, helps to define the amounts of nutrients and other dietary substances that promote optimum growth, development, and nutritional health. ARS scientists also study factors affecting the absorption of nutrients in the body. These studies, of course, require a precise understanding of the nutrient content of the diet. Many studies analyse diets for nutrient content; others calculate the nutrient content of diets using food composition tables. The individual centres focus on different research areas. For example, the centre at Tufts University in Boston studies the nutrition factors affecting the aging process, and the one in Houston at the Baylor College of Medicine studies the nutrition of infants and children. One of the research areas of the Human Nutrition Research Center at Beltsville, Maryland? is the development of methods for determining the composition of foods (see chap. 18).
Additional research on human nutrition requirements and the nutrient content of foods and diets is conducted at 58 state agricultural experiment stations. The Cooperative State Research Service serves as a link with the state system. Major research on food components as they relate to various diseases is conducted in another federal agency, the National Institute of Health (NIH), and by means of grants from NIH. While some of these studies include analyses of foods, others use USDA's standard reference tables adapted and extended to meet their own special needs.
Meat and Poultry Products Regulations
The Food Safety and Inspection Service (FSIS) safeguards the wholesomeness and nutritional quality of meat, poultry, and their products through inspection and analyses. This agency establishes standards, approves labels for meat and poultry products, and monitors the industry for compliance with inspection laws. As well as analysing the nutritional value of meat and poultry products, both domestic and imported, and determining the presence of food additives, it also assesses the nutritional equivalency of imitation and traditional foods and the effects of processing procedures on nutritional quality. For these varied purposes, FSIS conducts laboratory analyses and uses standard reference tables. The Food and Drug Administration (FDA) of the Department of Health and Human Services performs similar regulatory functions for foods other than meat and poultry.
Food Assistance Programmes
The Food and Nutrition Service (FNS) operates 10 major food assistance programmes. Through these programmes, populations at nutritional risk receive food or resources with which to obtain food. Some, such as the Food Stamp Program, provide assistance to the low-income population. Others are designed to help meet the nutritional needs of particular groups, such as children in school and in child care; pregnant and postpartum women, infants, and young children (WIC); and elderly persons. Studies of the effects of programmes on the diets of participants require food composition data, as does the development of standards for programme benefits and compliance.
The legal standard for benefits from the Food Stamp Program is the cost of foods in the thrifty food plan - the least costly of four food plans for nutritious diets developed and costed monthly by HNIS . These food plans reflect food consumption and nutrient levels as reported in the Nationwide Food Consumption Surveys (NFCS), changed only as necessary to meet nutritional goals for 17 food substances. The quantities of foods in the food plans are specified with the assistance of a computerized mathematical model.
Meal patterns for the school lunch and breakfast programmes are designed with the nutrient content of foods they contain as a major consideration. An alternative to using meal patterns as the basis for compliance in the school lunch programme is being field-tested; this involves instead the use of a nutrient standard for the lunch. HNIS has co-operated with FNS in developing software and special data bases for this test. Another programme, WIC, distributes vouchers for foods with nutrient content that will supplement the diets of participants.
National nutrition monitoring system
As part of the National Nutrition Monitoring System, HNIS maintains the National Nutrient Data Bank, sponsors related food composition research, and conducts surveys in order to monitor the food and nutrient content of American diets. The conversion of information on food consumption into nutrient consumption is the agency's major use of food composition data. The nutrient consumption of the nation's population is monitored at three levels: food in the US food supply, food used by households, and food eaten by individuals. To make these conversions, nutrient data are needed both for food as purchased and food as eaten; and data for each are needed by appropriate units of weight. Representative values - those for the food as purchased or as eaten throughout the country year-round - are appropriate for such conversions.
The food supply data, estimated for each year since 1909, show trends in quantities of nutrients available to the population and in the food sources of these nutrients. For example, the data show that dietary fat in the food supply has increased since the beginning of the century from 124 g to 166 g per person per day . The increase comes primarily from fats and oils. These statistics require that food composition data reflect the foods available for consumption during given periods. For example, the composition of poultry or pork in the 1980s is not the same as it was two decades earlier, and this series reflects those differences.
The food supply covers fewer than 400 basic foods - foods before they are combined into food mixtures. Nutrient data for these relatively few foods in their primary forms are generally readily available. Because of this, estimates of a nutrient's content in the food supply usually can be made before estimates for diets of households and individuals, which contain many more foods. An example is zinc . Several years ago, we had sufficient data to assess the food supply and recognize that the zinc levels of 11.5 to 12.5 mg per person per day since 1909 are not sufficient to provide Americans with the recommended dietary allowance of 15 mg per day . Sufficient data are only now becoming available on enough foods to allow us to assess zinc levels in household and individual diets. Many other countries make nutritional assessments of their food supplies based on statistics such as these.
Information on household food use and individual food intakes is collected by interview about every 10 years in Nationwide Food Consumption Surveys, the most recent of which was conducted in 1977|78. The next is planned for 1987. In 1977/78, data were collected in the 48 conterminous states for about 38,000 individuals in 15,000 households . The surveys showed the kinds and amounts of foods that households used during one-week periods and the food and nutrient intakes of individual household members for three-day periods.
The food used by the household, expressed in pounds of foods as purchased or brought in, is translated into the nutrient content of the household diet by using tables of the nutritive values of the edible parts of the food as purchased. Vitamin content is adjusted for usual losses during cooking. The food intake by individual household members, expressed in grams of foods eaten, is translated into nutrient content by using tables of the nutritive value of the edible portion of foods. To make these calculations requires representative values for each of the thousands of foods in forms that Americans buy for use at home and of foods that they eat both at home and away from home. Analyses are not available to provide reliable data for all nutrients for all of these foods. Therefore, some values are imputed from another form of the food or from a similar food to provide the best estimates of the nutrient content of diets.
Another data file is required for survey data analysis. It converts the quantity of household food reported in packages of rice, loaves of bread, cartons of milk, heads of lettuce, and cans of beans into pounds. It also converts quantities of food individuals ate - a hamburger pattie, a cup of milk, an orange, a piece of cake - into grams of edible food.
Over the decades, these surveys have required data not only on more and more foods but also on more and more nutrients. For example, data on various types of dietary fibre, carotenes, selenium, and tocopherol are now of special interest. Our nutrient data research is directed toward filling these and other needs. In the meantime, diet appraisals based on composition that are limited must be recognized as tentative and possibly misleading. Another concern in appraising diets - and one that can be addressed at this time only in a general way- is the availability of nutrients to the body as affected by the food carrier and other foods and drugs consumed.
As diets are monitored for more nutrients, the descriptive information required about the foods in the survey increases. For example, if information on only total fat in the diet is required, the specific ingredients in margarine are not of major concern. However, if the levels of fatty acids are to be measured, information on the types of oils in the margarine must be obtained. The sodium content of a vegetable depends on whether it was prepared from food in the raw, canned, or frozen, and on what seasonings were added in processing and preparation.
HNIS has considered such problems in planning the questionnaire and analysis for the Continuing Survey of Food Intakes by Individuals begun in April 1985 . New survey questions were introduced in an attempt to obtain the food descriptions needed for more reliable estimates of the levels of cholesterol, total fat, fatty acids, and sodium in diets. Some of this descriptive information the respondent may not be able to provide. The decision must then be made as to whether the missing information can be estimated with reasonable accuracy or whether such estimates are so poor as to be misleading.
Information on food composition has expanded and improved considerably since the last national survey was conducted in 1977/78. At that time, intakes were assessed for food energy; for the macro-nutrients - protein, fat, and carbohydrate; for four mineral elements - calcium, iron, magnesium, and phosphorus; and for seven vitamins - A, thiamine, riboflavin, niacin, B6, B12, and C.
For the new Continuing Survey, HNIS nutrient data specialists have updated and extended the data file to include 12 more nutrients and other food components than used in the previous survey: three classes of fatty acids, cholesterol, sodium, potassium, zinc, copper, carotenes, vitamin E, folacin, and dietary fibre. This data file will show the content of food energy and some 27 food components for 100-gram portions of each of about 4,000 foods as consumed, and will contain the most up-to-date information in USDA's Nutrient Data Bank. It is important that users of these data and of the survey results based on them recognize that values for these food components are not equal in reliability. For some food components relatively strong data support the values. Data for others- dietary fibre, vitamin E, and carotenes - are less well founded. If analytical data are not available, values are imputed.
The food consumption survey activities discussed are specified in an implementation plan for the National Nutrition Monitoring System sent to Congress by USDA and DHHS in 1981 . The core surveys of the system are USDA's Nationwide Food Consumption Survey (NFCS) and DHHS's National Health and Nutrition Examination Survey (NHANES).
NHANES collects information for one day's food intake and the frequency of consumption of selected foods; its primary focus is on the nutritional health status as determined by physical examination. The dietary data are assessed for nutrient content using composition tables, and the new data file developed for the Continuing Survey will be updated for use in future NHANES. Some analyses of NHANES data attempt to associate the nutrient content of a person's diet with his health status. Such studies might benefit from more precise data on the composition of the food eaten by that person than is given by the representative values in reference tables.
The statistics from NFCS and NHANES tell much about the diets and state of the nutritional health of the population. They make possible the monitoring of the dietary status of the American population to identify populations at risk, problem nutrients, food and eating patterns, and diet determinants. They have shown that many American diets do not meet desired dietary standards : many are short of recommended levels for certain nutrients such as calcium, iron, zinc, and folacin, some are short in vitamins A and C, and many exceed moderate levels of fat, sodium, and added caloric sweeteners.
A systematic exploration of uses of food consumption information was made by the Food and Nutrition Board (FNB) . Its report of June 1984, National Survey Data of Food Consumption: Uses and Recommendations, identifies the primary uses of food consumption survey data and recommends effective means of obtaining those data. Many of the uses listed are secondary uses, in that they require information on the nutrient content of diets and the nutrient contribution of specific foods to diets.
Dietary data from these surveys are used for many purposes: to monitor dietary status, to measure the economics of food consumption, to formulate and show the effects of food assistance and regulatory programmes, and to provide the basis for food selection guides - to name but a few.
USDA has for decades provided information to help Americans improve their food selections information based on knowledge of human nutritional requirements, food consumption, and food practices . The Dietary Guidelines published jointly by USDA and DHHS in 1980 and revised in 1985  advise Americans to: (a) eat a variety of foods; (b) maintain desirable weight; (c) avoid too much fat, saturated fat, and cholesterol; (d) eat foods with adequate starch and fibre; (e) avoid too much sugar; (f) avoid too much sodium; and (g) if you drink alcoholic beverages, do so in moderation.
Putting these guidelines into practice requires an understanding of the composition of foods. It is important to know the "good" sources of a nutrient - those foods of which a serving provides a substantial part of the day's need - and the "important" sources - those foods that make worthwhile contributions of a nutrient because substantial amounts of the food are consumed . "Important" nutrient sources have been identified by ranking the foods Americans consume by their average contribution of nutrients to the diet.
Eat a Variety of Foods
This is a simple guideline representing a complex food selection technique. What is intended is "Eat the kinds and amounts of foods that will provide the minerals and vitamins your body needs." If Americans are to select diets that provide the recommended amounts of essential nutrients, they must increase their understanding of food composition. To help them, educators must translate complex food composition tables, which were developed for researchers and professionals, into simpler forms .
Maintain Ideal Weight
NHANES estimates that one-fourth of all Americans are overweight . Weight control plans that call for a varied diet made up of low-calorie foods require the use of food composition tables. An USDA pocket calorie guide, Calories and Weight , gives such advice, as does Food 2: A Dieter's Guide .
Avoid Too Much Fat, Saturated Fat, and Cholesterol
Fat intakes over three days from our 1977/78 survey were generally above the 30 to 35 per cent of calories suggested by some authoritative groups . For example, among adults of 35 to 50 years of age, only 13 per cent of the males and 17 per cent of the females had fat intakes that provided less then 35 per cent of total calories . Over one-third of the respondents got 45 per cent or more of their calories from fat.
The amount of saturated fat in diets reported in NFCS has not been estimated. Average cholesterol intakes have been roughly estimated using the limited information available on the types of fats and oils consumed. Intakes are highest for adult males and teenage boys, at 400 to 525 mg per day [ 16].
Efforts to develop guidance that will help Americans avoid too much fat? saturated fat, and cholesterol are complicated by the occurrence of fat and cholesterol in many foods that are important for their contribution of nutrients in US diets. Solutions depend on knowing the fat, cholesterol, and vitamin and mineral content of foods. Food 3: Eating the Moderate Fat and Cholesterol Way addresses this issue .
Eat Foods with Adequate Starch and Fibre
When the fat in the diet is reduced, calories must come from other sources. This guideline stresses that the source should be foods rich in complex carbohydrates. Food composition tables identify these as dry beans and peas, nuts, seeds, vegetables, fruits, and grain products. Increasing the use of foods that are high in complex carbohydrate will also increase the amount of fibre in the diet. Food composition tables in Agriculture Handbook No. 8 have provided crude fibre values for some time; but these values are no longer considered useful. The content of dietary fibre, now believed to be more meaningful, is not known for many foods. To further complicate the matter, available values may not be comparable because of the lack of standard analytical methods. The new data file for the Continuing Survey provides the most up-to-date values for dietary fibre and imputes values where data are missing. However, the values are not sufficient at this time to estimate the dietary fibre content of American diets with any degree of precision.
Avoid Too Much Sugar
Sugar, as intended in this guideline, is not just sucrose but all caloric sweeteners eaten with foods or as ingredients in foods. The few composition tables that attempt to provide data on added sweeteners should be used with caution, since they are useful only for providing rough estimates of the intakes of added sweeteners in diets .
Avoid Too Much Sodium
The sodium content of diets is notably difficult to measure, but there is little doubt that Americans consume more sodium than they need . The amounts of sodium in many commercial products and those added in preparation and at the table are virtually unknown. Sodium Content of Your Food is a bulletin that provides sodium values for commonly used foods. Sodium, Think About It, published by the Food and Drug Administration and FSIS, groups foods by their sodium content for general guidance in following this dietary recommendation.
Food selection guides since the turn of the century have used food composition data as one of several bases. Atwater in 1894 suggested diets for the American male based on content of protein, carbohydrate, fat, and "mineral matter" . Other guides, including the Basic Four in the 1950s  and the Hassle-free Guide , focus on the types of foods that are important sources of vitamins and minerals. The Hassle-free Guide also considered calories, sugar, fat, sodium, and fibre. The dietary guidelines published in 1980  have been interpreted by USDA and DHHS at the federal level, by state extension services, by other local groups, and by the food industry. USDA efforts include consumer bulletins, such as Ideas for Better Eating , Food 2: A Dieter's Guide, Food 3: Eating the Moderate Fat and Cholesterol Way , and Sodium Content of Your Food .
The HNIS staff co-operated with the American Red Cross in developing a six-session nutrition course based on the dietary guidelines and other timely nutrition messages . This course, "Better Eating for Better Health," has been offered by local Red Cross chapters across the country, starting in 1984. Its food guidance system is a food wheel, with suggested servings from several groups of food. The wheel is supplemented with information on food composition and "trade-offs," or food substitutions - all based on food composition data .
The Extension Service - the educational arm of USDA - has nutrition specialists in every state and home economists in almost every county. Their nutrition-related mission is to improve food management skills, the quality of diets, and the nutritional health of the public by transferring research-generated knowledge. They help the public to understand how foods that differ in nutrient content can be combined in diets that are nutritionally sound. Food composition data are fundamental to the development of these educational messages. Many states have developed interactive computer programs for appraising the nutritional quality of diets, and use these programs as educational tools. HNIS and the Extension Service are initiating a joint project for a diet assessment system using data bases that will be updated regularly.
This review of food composition data needs illustrates that the uses of food composition data are numerous and that data needs differ.
Nutrients and other food components for which data are needed differ by:
- energy and proximate composition;
- plus selected vitamins and minerals;
- plus other food components of dietary and health concern;
- plus pesticides, residues, toxicants, and additives.
Foods for which data are needed differ by:
- stage in the production-to-consumption chain (food supply - pre-retail; food as purchased; food as eaten);
- amount of processing and preparation (raw carrots; frozen carrots; carrots frozen in butter sauce; carrots cooked from those frozen in butter sauce);
- nature of descriptive characteristics (grapefruit, pink grapefruit, pink grapefruit grown in Texas, pink grapefruit grown in Texas under specified conditions and picked x weeks before market).
Degree of precision and accuracy needed differs: specific food must be analysed;
- samples of food must be specific for cultivar, place grown, and other characteristics that affect composition;
- values must be representative of a food as consumed in the United States;
- representative values are required, plus imputed values if analytical data are not available.
Units of measure of food differ:
- values for edible part of a pound of food as purchased;
- values for 100 grams of edible food;
- values for a household measure (cup, slice, piece, etc.) of food.
Complexity of presentation format differs:
- for scientists;
- for educators and health professionals;
- for the general public.
Approaches to meeting data needs
HNIS attempts to meet most of these needs through its publications and computerized data tapes. Agricultural Handbook No. 8 was published in a single volume in 1963, and is being revised in 23 sections, each dealing with one group of foods . Each section contains tables giving representative values of the edible parts of a pound of food as purchased, or 100-gram portions of edible food, and of food by household measures. These tables cover food in its raw state, food as it is processed for market, and food as it is prepared for consumption. Mixtures as marketed and certain commonly used home-prepared mixtures are included. The tables show the number of samples and the standard error for each value. If analytical data are not available, the tables do not show a value.
Data are shown for moisture, energy, protein, total lipid, carbohydrate, crude fibre, ash, dietary fibre (insoluble), calcium, iron, magnesium, phosphorus, potassium, sodium, copper, manganese, zinc, ascorbic acid, thiamine, riboflavin, niacin, vitamin A, pantothenic acid, vitamin B6, folacin, vitamin B12, tocopherol, cholesterol, commonly occurring fatty acids, pytosterol, and amino acids. The published sections of Agriculture Handbook No. 8 present detailed information in a complex format designed to be useful to scientists. Its loose-leaf format allows information for a single food to be updated. Selected data are presented in ways that are more easily used by educators and the general public.
The tables of nutrient data are also available in machine-readable form from the National Technical Information Service, US Department of Commerce. Imputed values for nutrients for which analytical data are not available are given in special data files that represent the staff's best judgement based on analyses of other forms of the food or of similar foods. Such values are flagged on the tape. The Nutrient Data Bank also contains data separately for foods with different characteristics, some of which are not shown separately in the tables. Specific values can be made available on request.
HNIS does not attempt to estimate the levels of pesticides, residues, toxicants, and additives in foods, except those additives that contribute energy and nutrients. The Agency does not have its own laboratories for conducting special-purpose analyses. Certain other parts of USDA, mainly ARS and FSIS, do have such laboratories, which they use to meet their need for highly precise data.
Food composition data have come a long way since the Second World War years when the content of a few nutrients in the civilians' share of the food supply was calculated in USDA on a clanking calculator. This is to the credit of many: the HNIS Nutrient Data Research Branch and their extra-mural analytical programme, the ARS Nutrient Food Composition Laboratory, the food industry, and others who develop sound analytical methods and conduct analyses and share them for use in the Nutrient Data Bank. But there is more to be done. Some HNIS objectives are as follows:
1. Improve nutrient data documentation by implementing an objective system for evaluating and specifying the quality of the data presented.
2. Improve data bases for several food components - dietary fibre, carotenes, loco pherol, selenium, copper, manganese, folacin, chromium, and molybdenum.
3. Keep up with the food production, marketing, and consumption changes in the country by covering new foods and determining the effects of new procedures on nutrient levels.
4. Complete a computerized food formula (recipe) file to develop and document the nutrient content of home-made mixtures and to approximate ingredients in commercial mixtures in the data sets for use in national surveys. This file can be used to assess diets reported in surveys in terms of the basic foodstuffs they contain.
5. Develop guidelines for the proper selection and use of food composition data for a variety of purposes.
6. Encourage users to evaluate carefully the computerized data files they use.
7. Design tools for helping the public to understand that food composition information is useful in selecting nutritious and healthful diets.
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