The U.S. Food Supply Series, 1970 to 1994: Nutrient Availability and Policy Implications

Shirley Gerrior

The U.S. food supply series measures the amount of nutrients available per capita per day. This paper reviews trends in food supply consumption and nutrient levels for 1970 to 1994. Substantial change in the U.S. food supply during this period led to per capita availability increases for most nutrients, except for saturated fatty acids, cholesterol, and vitamin [B.sub.12]. Food and nutrient level trends are examined in terms of Federal dietary guidance, nutrition monitoring activities, and fortification policy. Future research directions are suggested to improve the quality of food supply estimates in terms of these activities.

Dietary guidance to improve the public health and well-being of Americans has been in place since early this century (25)--a period similar to that covered by the U.S. food supply series. The translation of this dietary guidance into recommendations for a healthful diet and the successful implementation of these recommendations require that the consumer has greater access to affordable health-promoting foods. Thus, the quantity and nutrient composition of the foods available for consumption are vital to increasing the prevalence of healthy eating. Technological alterations, the designing of foods, and enrichment and fortification policy during this century have increased the variety of foods in the food supply as well as enhanced the health benefits associated with these foods. For example, the removal of nutrients or dietary components from foods has increased the variety of lower fat dairy and leaner meat products in the food supply, while the addition of nutrients to food through enrichment and fortification has improved the nutritional quality of the food supply.

This article discusses trends in U.S. food and nutrient supplies since 1970, compares data for 1970 and 1994, and considers the significant implications of these data for food and nutrition policy. The U.S. food supply series measures the amount of food available for consumption per capita per year and the amounts of nutrients per capita per day (5, 14). It is the only continuous source of data on food and nutrient availability in the United States. Food supply nutrient estimates, extended back to 1909, were calculated for the first time during World War II to assess the nutritive value of the food supply for civilian use in the United States and to provide a basis for international comparisons with the food supplies of our allies.

Per capita food supply estimates provide unique and essential information on the amount of food and nutrients available for consumption. They are useful to assess trends in food and nutrient consumption over time, for monitoring the potential of the food supply to meet the nutritional needs of Americans, and for examining relationships between food availability and diet-health risk. Therefore, the U.S. food supply series is one of the five major components of the National Nutrition Monitoring and Related Research Program (NNMRRP), mandated by the National Nutrition and Related Research Program Act of 1990 (4). In addition, because the food supply series has measured food and nutrients over time using the same conceptual methodology, it is useful for evaluating the effects of technological alterations, advertising and promotion efforts, changes in marketing practices, and nutrition education policies. It also helps agricultural policymakers translate nutrient recommendations into goals for food production and supply levels to ensure that adequate nutrients are available to Americans (see box, "About the Data").

Food Consumption Trends Are Driving Major Changes in Nutrient Availability

During 1970-94, substantial change in the quantity and mix of foods in the U.S. food supply produced marked change in nutrient availability. Much of the change is due to advances in technology and alterations in marketing practices, as well as to Federal dietary guidance[1] to make healthy food choices that promote health and prevent disease. The introduction of many foods into the food supply since 1970 reflects industry's response to this dietary guidance and consumer demand for a variety of lowfat, flavorful, and nutritious food choices. Production techniques and marketing changes over the last two decades have been particularly responsive to and reflective of dietary recommendations for fat, saturated fat, and cholesterol. The creation of newly formulated foods or the modification of foods or ingredients used in foods has enhanced the health benefits of the food supply.

The food supply provides a wide variety of healthy food choices, but compliance with dietary recommendations is often slow and not easily achieved by the general population. For example, although Americans have made some positive dietary changes in terms of consumption of grain products, vegetables, and fruits and the use of lower fat animal foods from the dairy and meat groups, they are doing less well with overall consumption of sugars and sweeteners and total fat. This finding agrees with recent studies that found, on average, most Americans are not meeting recommended servings for most of the Food Guide Pyramid's five major food groups, particularly whole grains, fiber-rich fruit, and dark-green, deep-yellow vegetables, while consuming excess calories from fats and sugars (1, 7) from foods such as cheese, salad and cooking oils and shortening, and regular carbonated soft drinks, respectively.

Availability of Nutrients, 1970-94

Per capita nutrient estimates show higher levels for most nutrients in 1994 than in 1970, except for saturated fatty acids, cholesterol, and vitamin [B.sub.12] (table 1). The level of food energy reached an all-time high of 3,800 calories per capita per day in 1994, in part due to a higher level of carbohydrate. The considerable increase in carbohydrate reflects the increased use of both grain products and total sugar and sweeteners (specifically, corn syrup sweeteners) (fig. 1, p. 6). During the late 1980's, grains replaced sugars and sweeteners as the major source of carbohydrate. By 1994, grains provided 41 percent of the total carbohydrate in the food supply (fig. 2, p. 6).

[Figures 1-2 ILLUSTRATION OMITTED]

Table 1. The U.S. food supply nutrient per capita per day, 1970 and
1994

Nutrient (unit)                     1970      1994    Percent change

Food energy (Kcal)                 3,300     3,800           15
Carbohydrate (g)                     386       491           27
Protein (g)                           95       110           16
Total fat (g)                        154       159            3
Saturated fatty acids (g)             54        52           -4
Monounsaturated fatty acids (g)       63        65            2
Polyunsaturated fatty acids (g)       26        31           19
Cholesterol (mg)                     470       410          -13

Vitamin A (RE)                     1,500     1,520            1
Carotenes (RE)                       510       660           29
Vitamin E (mg)                        13.7      16.9         23
Vitamin C (mg)                       107       124           16
Thiamin (mg)                           2.0       2.7         35
Riboflavin (mg)                        2.3       2.6         13
Niacin (mg)                           22        29           32
Vitamin B6 (mg)                        2.0       2.3         15
Folate ([micro] g)                   279       331           19
Vitamin [B.sub.12] ([micro] g)         9.5       8.1        -15

Calcium (mg)                         890       960            8
Phosphorus (mg)                    1,460     1,680           15
Magnesium (mg)                       320       380           16
Iron (mg)                             15.4      21.2         38
Zinc (mg)                             12.2      13.2          1
Copper (mg)                            1.6       1.9         19
Potassium (mg)                     3,510     3,780            8

Between 1970 and 1994, the percent kilocalories from complex carbohydrate in the total food supply increased from 22 to 26 percent, and that from sugar decreased slightly from 25 to 24 percent. While these trends are consistent with dietary guidance to choose a diet with plenty of grain products and high in complex carbohydrates, Americans still need to work harder to consume less foods high in sugar. In 1994, Americans consumed a record high amount of caloric sweeteners. Much of this came from the increased consumption of carbonated soft drinks. Between 1970 and 1994, per capita consumption of these regular drinks increased from 22 gallons to 40 gallons, while that from diet drinks increased from 2 gallons to 12 gallons per capita.

As with carbohydrate, the levels of several vitamins and minerals rose because of the increased consumption of grain products. For example, levels of thiamin, riboflavin, and niacin,[2] which rose due to the increase in the proportion of enriched flour since 1970 (15), are higher still in the 1990's because of increased grain consumption in more recent years (table 1). In 1994, riboflavin contributions from grain products were similar to those from dairy products, the leading source of riboflavin in 1970. Likewise, niacin contributions from grain products in 1994 were similar to those from meat, poultry, and fish products, the leading source of niacin in 1970. Since 1970, the higher levels of vitamin [B.sub.6], folate, phosphorus, magnesium, iron, zinc, copper, and potassium are, for the most part, related to increases in grain consumption. Grain consumption contributed over one-fifth of the folate, phosphorus, and copper, over one-fourth of the magnesium, and over one-half of the iron in the food supply in 1994 (table 2).

Table 2. Percent contribution from grains for selected nutrients in the U.S. food supply, 1970 and 1994

Nutrient            1970   1994

Carbohydrate         35     41
Thiamin              40     55
Riboflavin           19     31
Niacin               28     40
Vitamin [B.sub.6]     8     13
Folate               13     22
Phosphorus           14     21
Magnesium            18     26
Iron                 37     51
Zinc                 12     18
Copper               17     23
Potassium             6     10

Another trend seen between 1970 and 1994 that is consistent with dietary guidance is the increase in vegetable and fruit availability. In 1994, vegetables and fruits made important nutrient contributions to levels of vitamin A, carotene, vitamin C, folate, and potassium in the food supply. Despite the fact that the vitamin A level increased only slightly due to a decrease in egg and organ meat consumption, larger nutrient contributions than in previous years came from the dark-green and deep-yellow vegetables in the vegetable group--the largest contributor of vitamin A to the food supply. Consumption of dark-green and deep-yellow vegetables increased from 23 to 28 pounds between 1970 and 1994, contributing to higher levels of both vitamin A and carotene in 1994 (fig. 3).

[Figure 3 ILLUSTRATION OMITTED]

Vitamin C reached a peak in 1994 due to increases in variety and year-round availability of fresh citrus fruits. Since 1970, fruits and vegetables have been responsible for about 90 percent of the vitamin C in the food supply. Also, higher levels of folate and potassium are associated with the trend in increased fruit consumption (as well as grain consumption). Although not contributing to an increase in potassium levels, the vegetable group continued to be the primary source of this nutrient from 1970 to 1994.

Trends in consumption of the dairy and meat, fish, poultry, and egg groups in the food supply are closely associated with levels of protein, fats, fatty acids, and cholesterol and to levels of selected nutrients, such as calcium and phosphorus in dairy foods, and iron, zinc, and vitamin [B.sub.12] in meat and egg products. The increase in protein from 1970 to 1994 is due mostly to higher consumption of poultry, and, to a lesser extent, grain products, cheese, and lowfat milks (figs. 1, 4, and 5).

[Figures 4-5 ILLUSTRATION OMITTED]

There was an overall shift in source's of fat from animal to vegetable (fig. 6) from 1970 to 1994. This was primarily caused by the increased use of salad dressings, cooking oils, and vegetable shortening[3] but is also reflected in changes in levels of fatty acids for animal foods. The lower level of saturated fatty acids shows the decreased use of whole milk and increased use of leaner red meats and poultry. Despite lower whole milk consumption, saturated fatty acids from dairy foods increased somewhat between 1970 and 1994 because of consistent year-to-year increases in per capita consumption of cheese. The higher level of polyunsaturated fatty acids reflects the increased use of vegetables oils. Higher vitamin E levels are related to this trend as well, with the fats and oils group providing over three-fifths of the vitamin E to the food supply between 1970 and 1994. The level of cholesterol, a dietary component of the lipid family and found only in animal products, declined because of the lower consumption of eggs and red meat and the shift from fluid whole milk to lowfat and skim milks (figs. 4 and 5). The lower level of vitamin [B.sub.12] in 1994 is also due to decreased consumption of eggs as well as organ meats.

[Figure 6 ILLUSTRATION OMITTED]

The dairy group is the primary source of both calcium and phosphorus, contributing about three-fourths of the calcium and one-third of the phosphorus in the food supply between 1970 and 1994 (fig. 7, p. 9 and fig. 8). An increased consumption of cheese was principally responsible for higher levels of both of these nutrients, with calcium and phosphorus contributions from cheese doubled from 11 to 23 percent and 5 to 10 percent, respectively, between 1970 and 1994.

[Figures 7-8 ILLUSTRATION OMITTED]

With the decline in whole milk consumption and the shift to lowfat and skim milk between 1970 and 1994, calcium contributions more than doubled from lowfat and skim milk, but were only one-third those from whole milk in 1970 (fig. 7). Overall, calcium contributions from beverage milks were less in 1994 than in 1970 due to the decreased consumption of these milks. Although lowfat and skim milk contributions to total magnesium in the food supply increased in 1994 over those in 1970, this increase was not enough to prevent the shift from the dairy group to the grain group as the main contributor of magnesium in 1994 (fig. 9).

[Figure 9 ILLUSTRATION OMITTED]

The meat, poultry, and fish group continued to provide important and relatively stable contributions of both magnesium and phosphorus and to be the primary contributor of zinc in the food supply between 1970 and 1994 (figs. 8-10). However, the higher level of zinc in 1994 was due to increased grain consumption as the zinc contributions from the meat, poultry, and fish group declined and those from dairy products remained stable during this period (fig. 10).

[Figure 10 ILLUSTRATION OMITTED]

Significant Implications of U.S. Food Supply Data for Food and Nutrition Policy

Public Health Issues: Nutrient Availability Compared With Federal Dietary Guidance

Whereas early dietary guidance was directed toward the avoidance of deficiency diseases, current guidance is focused on the role of the diet in the etiology and prevention of chronic diseases (see box, p. 12, "Federal Dietary Guidance"). The Recommended Dietary Allowances (RDAs) (11), established in 1943, have served as the basis for the nutritional content of foods and diets, and over the years, a nutritionally adequate food supply was linked to providing sufficient energy, macronutrients, and micronutrients to meet the needs of consumers (16). With expanded scientific knowledge of the roles of nutrients since the inception of the RDAs, the purpose of the food supply has become more complex, ranging from the prevention of classical nutritional deficiency diseases, such as rickets, to one of reduction of the risk of such chronic diseases as cardiovascular disease, cancer, and osteoporosis.

To better serve this purpose, food supply-related research is based on activities specified in the Ten-Year Comprehensive Plan (23), the basis of the planning and coordination of the NNMRRP. Per capita data indicate that the U.S. food supply is capable of providing recommended nutrient levels for the total population; however, dietary selection is quite variable and may not be adequate for some individuals because of social, cultural, and economic factors (13). The Third Report on Nutrition Monitoring in the United States (TRONM), prepared for the Interagency Board of the NNMRRP, has classified several food components as current or potential public health issues (table 3, p. 13) (4). Food components classified as current public health issues are associated with dietary intake disease risk, such as obseity, coronary heart disease, anemia, or osteoporosis. Those food components classified as potential public health issues require additional research to develop interpretive criteria to link monitoring data to functional or health outcomes and/or improved food composition data.

Table 3. Classification of food components as public health issues in the Third Scientific Report on Nutrition Monitoring(1)

                                                      Not current
Current public          Potential public               public
health issues           health issues                 health issues

Food energy             Total carbohydrate            Thiamin
Total fat               Dietary fiber                 Riboflavin
Saturated fatty acids   Sugar                         Niacin
Cholesterol             Polyunsaturated fatty acids   Iodine
Alcohol                 Monounsaturated fatty acids
Iron                    Trans fatty acids
Calcium                 Fat substitutes
Sodium                  Protein
                        Vitamin A
                        Vitamin C
                        Vitamin E
                        Carotenes
                        Folate(2)
                        Vitamin [B.sub.6]
                        Vitamin [B.sub.12]
                        Magnesium
                        Potassium
                        Zinc
                        Copper
                        Selenium
                        Phosphorus
                        Fluoride

Modified from: Third Report on Nutrition Monitoring in the United States (4).

(1) This classification of nutrients should be regarded as provisional. As new data become available, future assessments of public health significance and of the levels of monitoring needed will result in changes in the categorization of some food components.

(2) Since the publication of this classification table, the relationship of folic acid to neural tube defects has been much publicized. In 1996, FDA announced that effective January 1, 1998, folic acid must be added to most enriched flour, breads, corn meals, rice, noodles, macaroni, and other grain products. This action heightens the folate role in national nutrition monitoring, and reclassification of this nutrient may be necessary.

Currently, the intake recommendations for many nutrients and dietary components are under scientific evaluation by the Food and Nutrition Board of the Institute of Medicine, National Academy of Sciences as part of the Dietary Reference Intake project. To complement this evaluation and because of the important roles played by iron, folate, and calcium in public health and in nutrition and fortification policy, the intake and availability levels of each of these nutrients are compared with Federal dietary guidance.

Iron deficiency is the most prevalent nutrient deficiency in America, with some of the most serious concerns related to its effects on the health and development of infants and children (6). Infants, adolescents, and women of childbearing age are those who are most at risk of developing anemia. Their greater iron needs, due to rapid growth or excessive blood loss during menstruation, usually cannot be met by dietary intake alone.

In 1994, the level of iron in the food supply was about 6 mg higher than in 1970 (table 1). The trend towards increased iron reflects increased iron fortification of breakfast cereals and increased consumption of grain products between 1970 and 1994 (fig. 11). At 21.2 mg per capita per day, the average content of the food supply exceeded recommendations for all sex-age groups with the exception of pregnant women. This does not mean, however, that all Americans ingest the recommended amounts of iron, since food supply estimates can overestimate what is actually consumed.

[Figure 11 ILLUSTRATION OMITTED]

According to data from USDA's 1994 Continuing Survey of Food Intakes by Individuals (CSFII), Americans as a whole consumed an average of 136 percent of their Recommended Dietary Allowance (RDA) for iron from food sources (intake data do not include dietary supplements). However, whereas male adults 20 to 49 years old were getting 182 percent of their RDA, females of the same age were consuming 82 to 88 percent of their RDA, on average.

Epidemiological evidence indicates that low serum folate levels are associated with elevated serum homocysteine, an independent risk factor for vascular disease, and that the use of dietary supplements containing folate by females before they become pregnant and during early pregnancy is associated with a decreased incidence of some types of neural-tube defects (4). In response to this, the Food and Drug Administration (FDA) recently directed that a folate fortification policy of 140 [micro]g per 100 gm for cereal-grain products, along with fortification of ready-to-eat breakfast cereals up to 100 [micro]g per serving and 400 [micro]g per unit or serving for supplements, be implemented in early 1998 (22). FDA's goal is to increase folate intakes for the target population (women of childbearing age) as close as possible to recommended intakes while maintaining safe levels for all other people (26).

In 1994, the level of folate available in the food supply was about one-fifth higher than the level in 1970 (table 1). This is due to an increase use of grain products and citrus fruit. However, the vegetable and legumes, nuts, and soy groups continue to be the major contributors of folate (fig. 12). At 331 [micro]g per capita per day, the average content of folate in the food supply exceeded recommendations for all sex-age groups except pregnant women. According to estimates from USDA's 1994 CSFII, Americans as a whole consumed an average of 169 percent of their RDA for folate with no population subgroup falling below 100 percent of the RDA; however, the 1989 RDA does not account for the safety factor needs of folate for women of childbearing age.

[Figure 12 ILLUSTRATION OMITTED]

Calcium is essential for the formation of bones and teeth, and requirements increase significantly during adolescence, early adulthood, pregnancy, and lactation. Calcium is very important from a public health perspective because current calcium intakes may be insufficient to attain optimal peak adult bone mass and to prevent age-related loss of bone mass. Inadequate intake of calcium may increase the risk of osteoporosis, a condition in which decreased bone mass weakens bone. In 1994, a National Institutes of Health Consensus Development Conference on Calcium Intake recommended that the current RDA for calcium be increased to between 1,000 and 1,500 mg, depending on age and other health factors, to help reduce the risk of this disease (8).

The calcium level in 1994 was higher than in 1970 (table 1). With the decline in consumption of whole milk and beverage milks overall, increased calcium levels are due primarily to increases in cheese consumption (fig. 7). At 960 mg per capita per day, the average content of the food supply failed to meet calcium recommendations for all males and females 11 to 24 years of age and for pregnant and lactating women.[4]

According to estimates from USDA's 1994 CSFII, Americans as a whole consumed an average of 92 percent of their RDA for calcium. The intake by males ranged from 91 to 118 percent of the RDA and men 20 years and over averaged 107 percent of the RDA. The intake by females ranged from 67 to 82 percent of the RDA and women 20 years and over averaged 75 percent of the RDA. These calcium intakes indicate that individuals are not consuming enough of the foods rich in calcium available to them in the food supply, much less the amounts that are currently being suggested by many health experts. This finding has policy implications for nutrition educators as they design nutrition education programs to increase calcium consumption, especially for adolescent girls and women, and for policymakers as they consider strategies for improving calcium intakes of Americans.

The Role of Food Fortification in Meeting Public Health Objectives for Chronic Disease Prevention

Historically, especially during the 1930's and 1940's, the addition of nutrients to foods through enrichment and fortification has been an effective way to maintain and improve the overall nutritional quality of the U.S. food supply and to solve the public health problems seen earlier in this century (16,26). For example, enrichment of cereal-grain products has been an extremely effective means of enhancing the nutrient quality of the food supply and serves as a practical and effective public health strategy for providing required nutrients. Cereal grains are eaten by essentially all population groups. Other nutrient-deficiency diseases were dealt with by fortifying various foodstuffs with specific nutrients.

By the 1950's, four specific programs--fortification of salt with iodine; fortification of milk with vitamin D; enrichment of flour and grains with thiamin, riboflavin, niacin, and iron; and fortification of margarine with vitamin A--were in effect for the addition of nutrients to the U.S. food supply.

Over time, guidelines for food fortification have evolved, as interest in adding nutrients to foods has shifted from prevention of deficiency diseases to broader issues of improving overall health. Food fortification policy has also been established for other commodities and additional nutrients. Although grain products have proven to be the most suitable vehicles for fortification in the food supply, fortified foods also include (but are not limited to) ready-to-eat cereals, fruit drinks and juice, meal replacement bars and beverages, infant formulas, margarine, and milk-based products. Many juice drinks are fortified with vitamin C, which is the key vitamin provided by most juices and juice drinks. As a result of fortification, some juices and juice drinks are also a good source of calcium and vitamin A as betacarotene.

Nutrient additions supplement the amount of thiamin, riboflavin, niacin, iron, iodine, and vitamins A, C, and D in the food supply substantially and the prevalence of specific nutrient deficiencies in the population has been greatly reduced. In particular, the gradual rise in the percentage of white flour that is enriched has contributed to increased levels of thiamin, riboflavin, niacin, and iron (15), accounting for over half of the thiamin and iron, two-fifths of the niacin, and almost one-third of the riboflavin in the food supply (table 2) in 1994. Also, the fortification of margarine with vitamin A accounts for about 9 percent of the total vitamin A in the food supply.

Because the food supply series measures foods and nutrients over time, the impact of added nutrients for purposes of enrichment and fortification of basic food commodities can be gauged. This important association of the food supply with fortification policy continues to be monitored with research activities directed towards the evaluation and determination of nutrients added to the food supply for enrichment, fortification, and functional purposes.

If nutrient requirements can be met readily by the food supply without nutrient addition, then nutrition educators can develop programs to help individuals meet nutrient requirements or improve nutrient intakes. However, a dietary recommendation to increase intake of a particular nutrient may hinder the food supply's ability to provide an adequate level of that nutrient. In this case, policymakers need to consider fortification options or other strategies to improve the food supply. Most recently, the public health goal of increasing folate intakes for women of childbearing age to reduce the occurrence of neural-tube defects in infants led FDA to rule that cereal-grain products be fortified with folic acid by January 1, 1998 (22).

Future Directions

Scientific evidence on the relationship between diet and health and the importance of fortification in public health require accurate and updated information on the quality and composition of the American diet. Such information is used to determine the extent to which diets differ from Federal dietary guidance and to monitor the dietary and nutritional status of Americans. In order for policymakers to translate dietary guidance into goals for food production and Supply levels and to make appropriate decisions regarding food fortification, the link between food supply and food intake data needs to be better understood. This requires further research and analysis of these two types of data to recognize their differences and similarities. Additionally, to minimize the limitations of food supply data and to better translate per capita food consumption and nutrient estimates into intake data, improved food supply estimates of fats and oils and discard and processing factors are needed.

Also, research is needed to update the fortification data base that supports the U.S. food supply series. Several studies have looked at how the nutrient content of the food supply has been affected by enrichment and fortification (2,3,12). The earlier study (2) showed that fortification and enrichment of grain products provide a significant proportion of the thiamin, niacin, iron, and riboflavin supply for the average American. More recent studies (3,12) have examined the effect of food fortification in terms of distribution of nutrient intakes by population subgroups as well as overfortification of the food supply. Both studies acknowledge the importance of fortifying the food supply as a public health intervention to improve nutritional intake of a particular nutrient by a target population.

Nutrient data bases that account for added nutrients are limited and the U.S. Department of Agriculture (USDA) nutrient data bases do not routinely identify levels of added nutrients. As a result, the food supply fortification data base has not been updated since 1970, except for the percentage of flour, enriched. Since 1970, enormous changes in food industry fortification practices have occurred and both the range of fortified foods and the number of added nutrients have expanded. An updated version of USDA's food composition data base, designed to include nutrients added to foods commercially through enrichment and fortification, is needed to generate more accurate food supply nutrient estimates for policy work on fortification issues and nutrient recommendations. As a major component of the NMRRP, food supply nutrient estimates must be as accurate as possible to support policy decisions that improve the nutritional status of Americans.

About the Data

USDA's Center for Nutrition Policy and Promotion uses data on the amount of food available for consumption from USDA's Economic Research Service (ERS) and information on the nutrient composition of foods from USDA's Agricultural Research Service (ARS)[1] to calculate the nutrients available in the U.S. food supply. Nutrients reported include food-energy, energy-yielding components (carbohydrate, protein, and fat), cholesterol, 10 vitamins, and 7 minerals.

Food supply data, collected and published annually by ERS, estimate the amount of food available for consumption in the United States by measuring commodity flows from production to end uses, Food available for consumption is calculated as the difference between available commodity supplies (the sum of production, imports, and beginning-of-the-year inventories) and the sum of exports, year-end inventories, and nonfood uses. Foods are measured as primary commodities before they are combined with other foods or processed into final products seen in the market place.

The food supply consumption estimates reflect amounts of food available prior to moving through marketing channels not the amounts actually consumed. Therefore, the supplies are greater than what individuals ingest due to losses in trimming, cooking, plate waste, and spoilage that are not accounted for in the estimates. For example, the food supply estimates overstate human consumption of fats and oils, since large amounts are used for frying by fastfood establishments and later discarded as waste. Also, increasing proportions of the total turkey supply go into pet foods, but such use is included in per capita turkey estimates and thus overstate turkey consumption (14).

The food supply nutrient estimates are calculated by multiplying the per capita amount of each food by the nutrient composition of that food. The results from approximately 400 foods are then totaled for each nutrient and presented on a per day basis. As with the food supply estimates, the nutrient estimates presented here do not account for losses during processing, marketing, or home use and are better indicators of trends in consumption rather than actual amounts ingested. For example, vegetables generally lose nutrients when cooked in water, particularly water-soluble nutrients like vitamin C and thiamin.

Nutrients not included in these values are those from phosphorus contained in carbonated soft drinks, vitamin and mineral supplements, alcoholic beverages (or the grains and sugar used to make alcoholic beverages), baking powder, yeast, and certain vitamins and minerals used for functional or flavoring agents in foods. Nutrients added to foods commercially through enrichment and fortification are included in the nutrient values.

Food supply data differ from dietary survey data: food supply data measure food and nutrient availability as national totals whereas dietary survey data (such as USDA's Continuing Survey of Food Intakes by Individuals) provide data on food and nutrient intakes reported by individuals and households. Dietary or food intake surveys record food intake data over a specific time period and combine it with demographic information. These data are used to assess food consumption behavior and the nutritional content of diets for policy implications relating to food production and marketing, food safety, food assistance, and nutrition education.

Both the food supply and food intake data are major components of the NNMRRP, a set of related Federal activities intended to provide regular information on the nutritional status of the U.S. population. However, both have strengths and limitations that affect their ability to measure food consumption and their usefulness in dietary assessment. For example, food supply estimates reflect the amount available prior to moving through marketing channels, not the amount actually consumed. Thus, supplies are greater than what individuals ingest due to losses in processing, marketing, home use, and spoilage that are not accounted for in the estimates. Likewise, nutrient estimates determined for food supplies do not account for these losses and need to exceed those recommended for good health by a generous amount to account for such losses and to ensure adequate nutrients are available to the U.S. population. Also, these levels represent averages for the entire population. As a result, food supply data typically overestimate food and nutrient availability and are better indicators of trends in consumption over time rather than actual amounts ingested.

On the other hand, the quality of dietary or food intake surveys depends on the appropriateness of the methodology used for data collection and on the accuracy and completeness of the recall or recording of the individual. Underreporting of total diet or different food groups is common with these surveys. Because of such limitations, food intake surveys may underrepresent actual food intakes.

Due to the current limitations of these two types of data, their joint application is best directed toward trend analysis of food and nutrient consumption. The U.S. food supply series serves this purpose well since the conceptual basis for measuring food and nutrient estimates has remained the same over the series. However, apparent trends from food intake surveys may be misleading due to changes in survey design, sampling strategy, and interview methodology from one survey to another.

[1] Nutrient data used for the most recent update are from the Primary Nutrient Data Set developed for use with the 1994 Continuing Survey of Food Intakes by Individuals (CSFII) (17).

[1] Current Federal dietary guidance as used in this paper considers the following: Recommended Dietary Allowances (tenth edition) (11), Nutrition and Your Health: Dietary Guidelines for Americans (4th ed.) (20), The Food Guide Pyramid (18), and the Diet and Health Implications for Reducing Chronic Disease Risk (10). These serve as the basis for nutrition policies of the Federal Government. Earlier Federal dietary guidance, which influenced production and consumption practices in the late 1970's and 1980's, includes Dietary Goals for the United States (1977) (24), Healthy People: The Surgeon General's Report on Health Promotion and Disease Prevention (1979) (21), Nutrition and Your Health: Dietary Guidelines for Americans (1980) (19), and Diet, Nutrition and Cancer (1982) (9).

[2] Food composition data give only the amount of preformed niacin in food. Thus, per capita niacin estimates for the food supply refer to the availability of preformed niacin from foods--not that formed in the metabolism of tryptophan.

[3] See box "About the Data" for limitations of fat data.

[4] The food supply calcium level of 960 mg in 1994 was adequate to provide the RDA by sex-age group when the RDA was based on the population distribution as determined by Census. More of the population require 800 mg than 1,200 mg; thus 960 mg was sufficient on a national basis.

References

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(2.) Cook, D.A. and Welsh, S.O. 1987. The effect of enriched and fortified grain products on nutrient intake. Cereal Foods World 32(2):191-196.

(3.) Crane, N.T., Wilson, D.B., Cook, D.A., Lewis, C.J., Yetley, E.A., and Rader, J.I. 1995. Evaluating food fortification options: General principles revisited with folic acid. American Journal of Public Health 85(5):660-666.

(4.) Federation of American Societies for Experimental Biology, Life Sciences Research Office. Prepared for the Interagency Board for Nutrition Monitoring and Related Research. 1995. Third Report on Nutrition Monitoring in the United States. Volume 1.

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RELATED ARTICLE: Federal Dietary Guidance

Federal dietary guidance is outlined in Nutrition and Your Health: Dietary Guidelines for Americans and illustrated graphically in the Food Guide Pyramid (figs. a and b) (18,20). Both are designed to help Americans, 2 years of age and older, choose diets that meet their nutritional needs and improve health by reducing chronic disease risks. The fourth edition of the Dietary Guidelines bulletin, published in 1995, outlines seven dietary recommendations that consumers should adopt for better health:

* Eat a variety of foods

* Balance the food you eat with physical activity--maintain or improve your weight

* Choose a diet with plenty of grain products, vegetables, and fruits

* Choose a diet low in fat, saturated fat, and cholesterol

* Choose a diet moderate in sugars

* Choose a diet moderate in salt and sodium

* If you drink alcoholic beverages, do so in moderation.

The Dietary Guidelines bulletin recommends that people choose a diet that provides no more than 30 percent of total calories from fat and less than 10 percent of calories from saturated fat. Additionally, it discusses the role of enriched and fortified foods in the diet and highlights good sources of several nutrients of concern to public health.

Shirley Gerrior

Nutritionist Center for Nutrition Policy and Promotion

Lisa Bente

Nutritionist Center for Nutrition Policy and Promotion

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