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CFSAN/Office of Food Safety*
April 2001; Updated July 2008†
The TDS involves purchasing samples of food throughout the U.S., preparing the foods as they would be consumed (table-ready), and analyzing the foods to measure the levels of selected contaminants and nutrients. Dietary intakes of these analytes by the U.S. population are then calculated by multiplying the levels found in TDS foods by the average consumption amounts for each food. The overall strategy and goals of the TDS have remained constant since its inception in 1961, but the specific methodology has been revised periodically. Exhaustive histories of the TDS have been published elsewhere (See the list of references).
The number of different foods sampled in the TDS has increased from 82 food items when the study was initiated in the early 1960s to about 280 foods in the current program. The list of TDS foods is updated from time to time to reflect changing eating patterns in the U.S. The information reported on this website reflects two versions of the TDS foods list. The first was compiled in 1990 and altered slightly in 1991 when additional infant and toddler foods were added to provide more information on levels of pesticides and lead in the diets of young children. The second version was implemented in 2003. (See the comprehensive table of both the 1990/91 and 2003 food lists.) Foods lists prior to 1990 have been published elsewhere (reference list).
Besides changes in the number and types of foods purchased in the TDS, the way in which the foods are analyzed has also changed over time. In some of the earlier studies, similar foods were combined before analysis to form composites representing major commodity groups (e.g., dairy, meat, grains). Beginning in the early 1980s, TDS foods were analyzed individually; this approach is still used in the TDS today.
Sample collections (also referred to as market baskets) are generally conducted four times each year, once in each of four geographic regions of the country (West, North Central, South, and Northeast). Food samples are purchased by FDA personnel from supermarkets, grocery stores and fast food restaurants in three cities in the region and are shipped to a central FDA laboratory. The foods are then prepared table-ready and the three samples are combined to form a single analytical composite for each TDS food. Current TDS analytes include pesticide resides, industrial chemicals, radionuclides, and toxic and nutrient elements.
Numerous units within FDA participate in the operation of the TDS. The Center for Food Safety and Applied Nutrition, College Park, MD, provides overall management of the program and summarizes the laboratory results. FDA District Offices from across the U.S., within the Office of Regional Operations, collect the foods and ship them to the Kansas City District Laboratory, Lenexa, KS, where the foods are prepared and analyzed for pesticide residues and elements. Portions of the composites are sent to FDA's Winchester Engineering and Analytical Center, Winchester, MA, for radionuclide analyses.
The foods collected in the TDS (referred to as the TDS food list) represent the major components of the diet of the U.S. population. The food list is based on results of national food consumption surveys and is updated from time to time to reflect changes in food consumption patterns. Currently, there are about 280 foods collected and analyzed in the TDS.
The TDS analytical results reported on this website (from 1991 to the present) reflect two versions of the food list; the first was compiled in 1990 and the second in 2003. The 1990 version is based on the USDA 1987-88 Nationwide Food Consumption Survey (NFCS) (USDA 1990, Pennington 1992). The 2003 version is based on USDA’s 1994-96, 1998 Continuing Survey of Food Intakes by Individuals (CSFII) (USDA 2000). See the comprehensive table of both the 1990/91 and 2003 food lists.
Dietary exposure to TDS analytes can be estimated by multiplying the levels of the analytes found by the average amount consumed for each TDS food. The food consumption amounts for each TDS food have been compiled for the total US population and 14 age/sex subgroups listed below; these consumption amounts are collectively referred to as the TDS diets.
Both the TDS food lists and diets were compiled from national consumption survey data through a process of aggregating survey foods and consumption amounts. During the food consumption surveys, detailed information was collected on the types and amounts of food consumed by each survey participant. Over 5,000 different foods were reported in each of the USDA surveys that were the bases for the 1990/91 and 2003 food lists and diets. Although there are many fewer TDS foods (~ 280) than survey foods (> 5,000), the goal of the TDS diets is to account for total food consumption. To accomplish this, the survey foods were grouped (or aggregated) according to their similarity to TDS foods and a “mapping” file was created in which each survey food was assigned to one of the TDS foods.
After the mapping was completed, average per-capita (eater and non-eaters) daily consumption amounts were calculated for each survey food and population group. Finally, the consumption amounts of all survey foods assigned to a TDS food were subtotaled to derive the TDS diet consumption amount for that food. The TDS diets assume that the analytical profile of the survey foods would be similar to that of the TDS foods to which they are assigned, and that the TDS diets could provide an estimate of total dietary exposure to the analytes from all foods in the diet – not from the TDS foods alone.
Three versions of the TDS diets are available below. Each file is a self-extracting compressed (zipped), tab-delimited text file** that can be downloaded, decompressed (double-click the file or use a program like Stuffit Expander), and imported by database or spreadsheet software. For best viewing and data manipulation, the text files should be saved and then opened from a database or spreadsheet program such as Microsoft Excel, Corel QuattroPro or Lotus 1-2-3.:
The mapping file used to create Versions 2 and 3 of the TDS diets is available here as a compressed, tab-delimited text file**. (The mapping file for Version 1 of the TDS diets is not available in electronic format.)
*Previously Office of Plant and Dairy Foods.
**Help with compressed files
†This document was originally issued April 2001, and updated June 2003, September 2004, September 2005, August 2006, March 2007 and July 2008.
