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FOOD SUPPLY METHODOLOGIES

The databases used to calculate food supply nutrient estimates are continually evolving. New sources of information are applied to food supply methodologies to reflect market conditions and technological advances better. These changes, along with the food industries' response to Federal dietary guidance and the consumer demand for healthier food choices, have influenced the U.S. food supply. Selected methodologies are discussed to provide pertinent information on quantity and nutrient estimates for 1909-2004.


DAIRY

Since the early 1900s, the butterfat content of whole milk declined from 3.75 percent to 3.27 percent in the late 1990s. Demand by the consumer for lower levels of butterfat in milk products, Federal standards on lower minimum levels of fat in milk products, and changes in types of cows bred for milking contributed to this decline. In fact, the higher fat milk of the 1950s is almost entirely gone from the market. Revised butterfat data are applied to per capita consumption estimates for fluid milks (whole, lowfat, and skim milk) to separate into their respective fat and residual components. This results in larger quantities of the residual component and smaller quantities of the fat component for these products over the series.

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RED MEAT

The red meat industry has altered a number of marketing practices in the past three decades with ramifications for the U.S. food supply series. Specifically, feeding practices, genetic and animal management practices, meat handling, and merchandising practices have been modified to improve production efficiency and to respond to consumer's health concerns about dietary fat and red meat. Resultant changes in the quantity and quality of red meat available for consumption in the food supply required that adjustments in the nutrient data bases be made beginning with the year 1955. These adjustments compensate for quantity overestimates previously reported for the mid-1950s to the present and reflect up-to-date nutrient information. Overall, closer trimming of fat and more bone removal have resulted in a lower ratio of available carcass for retailers and consumers. A conversion factor for meat is used to calculate the dressed-meat equivalent of bone-in cuts and boneless retail cuts. In the U.S. food supply series, an assumption is made that a certain percentage of carcass weight (fat, bone, and connective tissue) is removed or lost before the product reaches the retail level or consumer.

Beef

Two sets of conversion factors used to calculate beef quantity and nutrient estimates are revised periodically to account for variations in quality and yield of the product and in marketing practices. These conversion factors are based on changes in animal husbandry or technology, marketing practices of fat and bone at the packer or retail level, or a combination thereof at a specific period over the series. One factor accounts for specifications related to closer fat trim by packers (carcass-to-wholesale) and the other adjusts for the closer trimming of fat and increased removal of bone by retailers (carcass-to-retail). For beef, Yield Grade is a major consideration in the adjustment in animal composition because the lower the Yield Grade, the less fatty the animal carcass. Also, the current retail practice of fat trim replaces the 1/2-inch trim of the 1970s and 1980s with 1/8-inch trim.

Pork 

For pork, two conversion factors used for carcass-to-retail calculations have been adjusted downward for the series beginning in 1955 to better reflect the changing mix of lean and fat on the carcass and the smaller percentage of carcass available for fat cuts. These factors account for the separation of wholesale pork into lean and fat cuts during processing and exclude fat cuts from the total retail carcass weight. The revised factor for fat cuts are based on bellies (primarily bacon) percentage yield from bone-in trimmed wholesale cuts. Since the late 1960s this yield has decreased and in the 1990s was about one-half that of 1965.

Veal and Lamb

Fewer changes have occurred in the production and marketing of veal and lamb than of beef and pork. Since the early 1990s many retailers have been trimming lamb products to a 1/8-inch trim and the PDS values used in the lamb nutrient data base are reflective of leaner cuts for more recent years. Also, carcass-to-retail conversion factors used for veal from the early 1960s have been changed. These factors are more reflective of the cattle industry and more representative of the nutrient contributions from veal to the food supply.

Game

Prior to 1966, game estimates for deer, duck and geese were provided by ERS or estimated from ERS data. Beginning with 1966, game estimates were based on game harvest data from the States or national sources and the types of game reclassified into one of four categories; deer, big game (excluding deer), small game, and water fowl. Carcass weights for deer, big, and small game were calculated with data provided by the individual States or from the Wildlife Management Institute. Carcass weights for duck and geese were calculated from data provided by the U.S. Fish and Wildlife Service. A weighted average was used for each of the four categories. Harvest data are totaled for a particular year and adjusted based on carcass weight. These estimates are divided by the Census population data to calculate per capita quantity and nutrient estimates.

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FISH

Fish production data include fish caught by commercial fishing vessels, noncommercial sources, and aquaculture. (Game fish is not included). Canned and cured fish are processed from fish caught and counted separately from those that are caught for fresh and frozen distribution. Estimates for some fish in the food supply are reported as broad categories that include a number of species based on lipid content. The categories include: fatty fish--those containing more than 5-percent fat; lean fish-those containing 5-percent or less of fat; and ground-dwelling fish. Previously, no nutrient composite had been used for ground-dwelling fish. In 1997, a nutrient composite was defined and calculated for ground-dwelling fish using the same procedure as used for the fatty and lean fish composites.

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VEGETABLES

Vegetable Composites

The nutrient estimates for miscellaneous canned, fresh and frozen vegetables have been revised. These nutrient estimates are based on composite vegetable data--a mix of vegetables reflective of a variety of vegetables consumed during specific years. Historically, nutrient data for these composites were hand calculated and entered into the food supply nutrient database with no direct link to the PDS. For canned vegetables the new composites are more reflective of consumption miscellaneous vegetables than previously reported. Each vegetable in the composite is directly linked to the Primary Data Set, thereby bringing the nutrients associated with a particular vegetable directly into the nutrient database.

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BREAKFAST CEREALS

The reporting of per capita consumption of breakfast cereals has changed over the food supply series. Cereal quantities, based on type of cereal, have been adjusted and nutrient composites developed to best reflect the nutrient content of the cereals as reported by ERS. For example, from 1909 to 1965, ERS reported per capita estimates for wheat and corn cereals as individual items, but did not account for cooked and ready-to-eat cereal quantities, separately. These items are listed as "grain, wheat cereals, 1909-65, total" and "grain, corn cereals, 1909-1965, total" under grouping level, item. (See Food Supply Database). Beginning in 1966 ERS reported corn and wheat cereals separately as to form (i.e. ready-to-eat or cooked). From 1966 to the present, ready-to-eat cereal, is listed as, "breakfast cereals, RTE", and cooked cereals as "grain, breakfast cereals, cooked" under the grouping level, item. (See Food Supply Database)

In 1999, an adjustment was made to ERS quantity data for wheat flour, corn meal, rice and oat grains to ensure that individual grain contributions from ready-to-eat cereals and cooked cereals were not double counted in the food supply series. A percent share of each cereal grain (wheat, corn, rice or oats) from breakfast cereals was applied to the total ERS quantity for an individual grain (wheat, corn, rice or oats) and a new percent share calculated for each of the flour commodities. Percent share contribution of breakfast cereal grains was determined from Census of Manufacturers, Flour Milling data for specific year periods. Quantity grain data in this report may be less than in previous years because of this adjustment.

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Ready-to-Eat Cereals

From 1966 to 1973 the percentage contribution of each cereal (wheat or corn) was determined and applied to the per capita estimates for the total ready-to-eat cereal, and subsequently linked to nutrient data specific to these two cereals. Beginning in 1974, ERS quantity data on ready-to-eat cereal were directly linked to a composite reflective of a number of cereals, not just wheat and corn. This composite includes wheat, corn, oat, rice, and mixed grain. The nutrient contribution from each of these cereals in the composite is based on cereal production data from the Census of Manufacturers and is updated every five years. In 2000 ERS ceased to report the quantity of RTE cereal.

Cooked Cereals

Beginning in 1966, per capita estimates of cooked cereals were reported by ERS as a total. Nutrient estimates reflective of this total-wheat, oat, mixed grain, and instant cereals-are based on cereal production data from the Census of Manufacturers and is updated every five years.

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FORTIFICATION

A method was developed to revise the food supply fortification files using two types of fortification files: historical files and dynamic or active files. Data from these files may be accessed by clicking on Food Supply Database: Fortification. Historical fortification files contain estimates of added nutrients by year and nutrient for a specific commodity or commodity category. These estimates were derived from a special survey designed by the U.S. Department of Agriculture and included as a component to the 1970 Census, conducted by the Bureau of Census. Absolute amounts of nutrients added by manufacturers and distributors of vitamins and minerals were directly entered into the food supply fortification file for a specific commodity. No link is made to the commodity's quantity data. Some food commodities, have only historical files, because information does not exist to estimate added nutrients as fortifications. These food commodity categories are: dairy products, fruit and fruit juices, and miscellaneous foods. Otherwise, historical files generally contain added nutrient data from the data of initial enrichment (or fortification) of a commodity to 1969 (i.e. rice, cornmeal/grits, margarine), 1973 (i.e. ready-to-eat cereals) or 1973 (i.e. flour and semolina), depending on the commodity. With the exception of selected grain products, nutrient data from historical files may only be viewed by the Internet user at the group level of a commodity. Active files link commodity quantity data directly to nutrient data, for a specific year based on the enrichment/ fortification policy for that year. A fortification query of these data will provide the nutrient total per capita per day as well as the contributions provided by the un-enriched/unfortified commodity and the enriched/fortified commodity. Active files are available for rice, cornmeal/grits, and margarine from 1970; breakfast cereals from 1974; and flour and semolina from 1974.

CNPP consulted with members of the Food Industry and Trade Associations, fortification policy/food regulatory staff at the Food and Drug Administration, academic experts in food science and nutraceuticals, and chemical suppliers of added nutrient formulations to establish or verify fortification levels of several food supply commodities.

For additional information regarding fortification in the U.S. food supply see The Nutrient Content of the U.S. Food Supply 1909-2000 on our related publications link or contact us at john.webster@cnpp.usda.gov .

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PYRAMID SERVINGS

The Interactive Food Supply (IFS) provides pyramid servings estimates for each of the major Pyramid food groups and subgroups. This feature expands the usefulness of the food supply data as it allows researchers and policymakers to gauge the availability of food in terms of current dietary guidance.

The Pyramid servings database used in the IFS was based on a multistage process designed by ERS. ERS adjusts aggregate food supply data -- non-edible food parts and food lost through spoilage, plate waste, and other losses in the home and marketing system -- and converts the remaining supply into daily per capita servings. The current Pyramid Servings data in the IFS is based on the 1992 Food Guide Pyramid. The Pyramid Servings data base will be updated to reflect the new 2005 MyPyramid recommendations in the near future.

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