Research Uses of the HEI

What is the Food Stream?

The Healthy Eating Index (HEI)-2015 and its predecessors, the HEI-2010, and the HEI-2005, are versatile metrics that can be used in population monitoring, nutrition surveillance, epidemiologic and economic research, and evaluation of nutrition policies and interventions. In addition to use in multiple types of research study designs, the HEI can be used to study multiple levels of the food stream.

The food stream refers to the flow of foods from agricultural production, through processing and distribution channels, to the food that ends up on our plates. This is important to study because individuals do not make food choices in isolation. Rather, their eating behaviors are influenced by a myriad of contextual factors, including what types of foods are available to them where they live, work, and shop.

Increasingly, nutrition researchers are realizing that if we can characterize all the levels of the food stream, we can build a better understanding of influences on individual behavior. Examining the healthfulness of the US food supply, the output from major producers, the menu of offerings in a school system, sales in a local grocery store, or individual-level diets could provide insights into the extent to which individuals have the capacity to make food choices that are consistent with dietary guidelines.

The HEI is an especially valuable tool in this regard because it can be used to evaluate any mix of foods. Since 2005, the standards for HEI have been density-based (e.g. amounts per 1,000 kcal) rather than absolute amounts, and rely on a common set of standards. Therefore, the HEI can be applied to the diets of individuals and to various levels of the food stream.

Image: an arrow shows the flow of foods through the four levels of the food stream: National Food Supply, Food Processing, Community Food Environment, and Individual Food Intake.
HEI Scoring Illustration
Figure 1: summarizing the three steps for deriving HEI scores across each of the four levels of the food stream. Read the following sections for a complete explanation.

Figure 1: summarizing the three steps for deriving HEI scores across each of the four levels of the food stream. Read the following sections for a complete explanation.

Research Studies at Different Levels

Regardless of the level of the food stream, the basic steps for deriving HEI scores are the same. However, the food and nutrient databases required vary by level, as shown in the HEI Scoring Illustration.

Any given set of foods at each level of the food stream can serve as the unit of analysis when employing a version of the HEI from 2005 to the present. At any single level, the index can be used to describe and evaluate a set of foods or to examine relationships between the quality of a set of foods and some other factor. Alternatively, it can be used to examine relationships among multiple levels of the food stream, such as the influence of changes in the quality of manufacturer's output on the quality of individual dietary intake. The interpretability and comparability of studies of this nature are simplified because the HEI can be applied in these various ways at multiple levels.

Additional details on the types of studies that can be conducted at the various levels of the food stream are provided below. The way the HEI is implemented and analyzed varies according to the type of study and level(s) being examined. For more information about this, see the Choosing a Method webpage.

National Food Supply

The amount and types of foods available in the food supply are the result of domestic production and imports, after accounting for exports, nonfood uses, inventories, and farm uses. The national food supply might be considered the "headwaters" of the food stream, as it represents the source of all agricultural commodities that flow downstream to manufacturers, food outlets, and markets, on their way to individuals. This mix of commodities must be appropriately for all individuals to have access to a healthy diet.

Sample Studies for the National Food Supply

The HEI can be used to answer questions about the national food supply. Below are example research questions that have been asked in the past and corresponding references.

Questions: Is the US food supply sufficiently balanced to provide the recommended proportions of various foods and nutrients? How has this balance shifted over time? Have some areas of the food supply changed more than others?

References:
Krebs-Smith SM, Reedy J, Bosire C. Healthfulness of the US food supply: little improvement despite decades of dietary guidance. Am J Prev Med. 2010 May;38(5):472-7.

Miller PE, Reedy J, Kirkpatrick SI, Krebs-Smith SM. The United States food supply is not consistent with dietary guidance: Evidence from an evaluation using the Healthy-Eating Index-2010. J Acad Nutr Diet. 2015 Jan;115(1):95-100.

Question: How can the HEI-2005 be applied to the food environment?

Reference: Reedy J, Krebs-Smith SM, Bosire C. Evaluating the Food Environment: Application of the Healthy Eating Index–2005. Am J Prev Med. 2010 Feb 18.

Steps

Steps 1 and 2: Identify the set of foods under consideration and determine the amount of each relevant dietary constituent in the set of foods

At the national food supply level, the first two steps in calculating HEI scores are intertwined by the databases used to enumerate the set of foods and provide the necessary compositional information. In contrast to other levels, researchers do not need to capture food supply data de novo, but rather can rely on publicly available databases.

Analyses using the HEI at the national food supply level reflect the set of foods that enter retail distribution channels. In the United States, quantities of each commodity are estimated by summing total annual production, imports, and beginning inventories and then subtracting exports, ending inventories, and nonfood uses. By dividing these aggregate amounts by the estimated population of the country, per capita estimates can be derived. The US Department of Agriculture (USDA) has provided such data through their Food Availability Data System, and corresponding Nutrient Availability Data.

The USDA also provides Loss-Adjusted Food Availability Data (LAFAD), which accounts for food spoilage, plate waste, and other losses. Waste is an important consideration in calculating the HEI because the components are density-based, and differential losses across food categories, if unaccounted for, could lead to difficulties in interpretation. Another advantage of the LAFAD is that quantities are provided in units such as cups and ounces, rather than pounds per person per day, and this allows for simpler calculation of the HEI. Because the data represent individual commodities and do not include any mixed dishes, such as those that complicate analyses at other levels, no disaggregation of foods is needed.

The United Nations' Food and Agriculture Organization (FAO) also publishes Food Balance SheetsExternal Web Site Policy, which are comparable, but not identical, to the US Food Availability Data in their derivation. The advantage of these data is that they are available for a wide range of countries, using a similar methodology, which makes them attractive for cross-country comparisons. However, because the associated nutrient data are limited and the waste adjustments used are not comprehensive, certain assumptions must be made and care is needed in interpretation.

Step 3: Derive pertinent ratios and score each HEI component using the relevant standard

For studies of the US food supply, the relevant dietary constituents needed to calculate the HEI scores are derived from the LAFAD and the Nutrient Availability Data. The Nutrient Availability Data require calibration to the LAFAD because they are not adjusted for waste in the way the LAFAD data are. For variables requiring the LAFAD, some can be obtained directly, whereas others require the application of assumptions and/or imputations.

At the food supply level, the amount of each dietary constituent is summed over all food commodities in the food supply and expressed as a ratio to total energy or, in the case of fatty acids, to total fatty acids. The resulting ratios are compared with the applicable standards for scoring.

Using the Total Fruits component as an example:

Graphic showing the mathematical formula for the described process: Dividing the sum of F for the set by the sum of E for the set gives the Assign Score for the set.

Where F = total cups of fruit in the food supply for a given year and E = total energy content of the food supply for a given year.

SAS macros are available for implementing step 3.

Food Processing

The next stop along the food stream for many foods in the United States is the manufacturer level, where agricultural commodities are processed into food products. This is the one level of the food stream to which the HEI has not yet been applied, but studies characterizing the output of major manufacturers could be valuable, considering their early position in the food stream and potential influence on levels further downstream.

For example, the HEI could be useful in examining the effects of the Healthy Weight CommitmentExternal Web Site Policy. That effort involves about 150 food companies who have collectively pledged to remove 1.5 trillion calories from the food supply by 2015; by 2017, these companies had removed 6.4 trillion calories from the food supply. Although the HEI is not necessary to evaluate whether they meet that goal, it could be used to examine whether their collective output has a higher diet quality after this effort is realized than before.

Obstacles to employing the HEI at this level relate to the lack of available data. For example, companies do not typically release information quantifying their total output of products. Even if such amounts could be obtained or reasonably estimated, data also are lacking on the composition of processed unprepared foods, such as macaroni and cheese or cake mix, which represent many of the foods associated with this level.

To calculate an HEI score, compositional data are needed in terms of both nutrients and food groups. For all packaged foods, the requisite nutrient composition data are available on the Nutrition Facts Panel, but data on the quantities of fruits, vegetables, whole grains, added sugars, and other components that also are required to calculate the HEI are not. Estimation of these components requires a specialized database that can disaggregate the product into its ingredients and tally the quantities of those ingredients with those of similar items. As described below, that type of database is available for ready-to-eat foods from Community Food Environment outlets and the Individual Food Intake level, but it is lacking for less-than-fully-prepared foods at the Food Processor level.

Steps

Step 1: Identify the set of foods under consideration

At the food processing level, the set of foods under consideration might be the output of a given manufacturer or group of companies, such as those taking part in the Healthy Weight Commitment. The ideal way to capture such data would be to get them directly from the manufacturer(s). Methods for researchers to gather this information themselves, using available data on foods in the marketplace, have not been developed, as research at this level has been held back by a lack of available nutrient and food group compositional databases.

Step 2: Determine the amount of each relevant dietary constituent in the set of foods

There are several food composition databases for packaged foods and beverages sold in the US. A free, publicly available database is the USDA’s Global Branded Food Products Database in FoodData Central. A fee-based resource is the Gladson Nutrition DatabaseExternal Web Site Policy. Both databases supply ingredient list and nutrient composition for several nutrients including energy, fatty acids, and sodium. Therefore, the nutrient information needed to calculate the HEI is available; however, the food group content is missing. Both nutrient and food group composition data are required to evaluate quality using the HEI. To facilitate research on food processing using the HEI, databases should also include food groups based on US dietary guidelines.

Step 3: Derive pertinent ratios and score each HEI component using the relevant standard

Once food group compositional databases are available at this level, calculation of the variables, ratios, and scores will be straightforward. The same SAS macros provided for implementing this step at the food supply level could be used at this level.

Community Food Environment

The Community Food Environment represents all of the places where individuals acquire foods and beverages. This includes food retail outlets where foods or beverages are sold (e.g. stores, online retailers, farmer’s markets), restaurants where prepared foods are both sold and consumed (e.g. full-service and quick-service restaurants), and non-monetary methods of food procurement (e.g. charitable food outlets, home gardens, etc.), among other food sources.

At any of these locations, the HEI can be applied to the set of foods available, marketed, served, sold, or consumed. For example, if a fast food restaurant was studied, the set of foods available corresponds to the menu options available to consumers whereas the set of foods served might use sales data for the same restaurant to study the impact the restaurant has on eating habits in that location. The HEI can also be used to compare diet quality across different categories of food outlets.

Sample Studies for the Community Food Environment

The HEI can be used to answer questions about the community food environment. Below are example research questions that have been asked in the past and corresponding references.

Comparison Across Outlets

Questions: How do Healthy Eating Index scores compare across the four primary types of food outlets? How has the quality of foods and beverages consumed by Americans from these food outlets changed over time?

Reference: Vinyard M, Zimmer M, Herrick KA, Story M, Juan W, Reedy J. Healthy Eating Index-2015 Scores Vary by Types of Food Outlets in the United States. Nutrients. 2021;13(8):2717.

Retail Food Outlets

Questions: To what extent do American’s grocery purchases align with the Dietary Guidelines for Americans? How does this vary by geographic region, income, and race?

Reference: Volpe, Richard, and Abigail Okrent. Assessing the Healthfulness of Consumers’ Grocery Purchases, EIB-102, US Department of Agriculture, Economic Research Service, November 2012.

Questions: How closely do foods featured in weekly supermarket sales circulars conform to dietary guidance? How does this compare to the US population’s intakes?

Reference: Jahns L, Scheett AJ, Johnson LK, Krebs-Smith SM, Payne CR, Whigham LD, Hoverson BS, Kranz S. Diet Quality of Items Advertised in Supermarket Sales Circulars Compared to Diets of the US Population, as Assessed by the Healthy Eating Index-2010. J Acad Nutr Diet. 2016, 116, 115–122.

Ready-to-Eat Food Outlets

Studies of food outlets and other settings where people purchase or are served ready-to-eat food -- such as cafés, restaurants, and schools -- do not have the same limitations regarding compositional databases as those of stores, because the foods served are ready-to-eat, which enables the comprehensive databases that have been developed for the individual level generally to suffice.

Question: How can the HEI-2005 be applied to the community level of the food environment such as the dollar menu displayed at a fast-food restaurant?

Reference: Reedy J, Krebs-Smith SM, Bosire C. Evaluating the Food Environment: Application of the Healthy Eating Index–2005. Am J Prev Med. 2010 Feb 18.

Question: How do five popular fast-food chains’ menus compare to dietary guidance?

Reference: Kirkpatrick SI, Reedy J, Kahle LL, Harris JL, Ohri-Vachaspati P, Krebs-Smith SM. Fast-food menu offerings vary in dietary quality, but are consistently poor. Public Health Nutr. 2013, 17, 924–931.

Question: How does the quality of meals consumed by US adults compare at full-service and fast-food restaurants and over time?

Reference: Liu J, Rehm CD, Micha R, Mozaffarian D. Quality of Meals Consumed by US Adults at Full-Service and Fast-Food Restaurants, 2003–2016: Persistent Low Quality and Widening Disparities. J. Nutr. 2020, 150, 873–883.

Food Assistance & Charitable Food Outlets

Questions: Can the Healthy Eating Index be applied to the hunger relief setting? What is the nutritional quality of foods and beverages ordered by food shelves from food banks?

Reference: Nanney MS, Grannon KY, Cureton C, Hoolihan C, Janowiec M, Wang Q, Warren C, King RP. Application of the Healthy Eating Index-2010 to the hunger relief system. Public Health Nutr. 2016, 19, 2906–2914.

Question: How do foods and beverages provided in a Montana backpack program compare with the 2010 Dietary Guidelines for Americans?

Reference: Byker C, Smith TM. Food assistance programs for children afford mixed dietary quality based on HEI-2010. Nutr. Res. 2015, 35, 35–40.

Question: What is the nutritional quality of food packages offered in the Food Distribution Program on Indian Reservations?

Reference: Shanks CB, Smith T, Ahmed S, Hunts H. Assessing foods offered in the Food Distribution Program on Indian Reservations (FDPIR) using the Healthy Eating Index 2010. Public Health Nutr. 2016, 19, 1315–1326.

Steps

Step 1: Identify the set of foods under consideration

Aspects of the community food environment that could be evaluated with the HEI include the set of foods and beverages offered, served or sold at markets, outlets, schools and other institutions. Foods offered can be operationalized by enumerating the set of foods and beverages on a menu (for example, from a school's lunch program) or otherwise offered for sale (for example, in a grocery store's weekly ad). Foods served could be defined, for example, as the total foods and beverages actually served by a school over a given period. Likewise, foods sold could be represented by the total sales for a neighborhood grocery store. It is generally easier to obtain information on foods and beverages offered than served or sold, as the latter are not as readily available and generally require cooperation from the market, outlet, or institution.

Step 2: Determine the amount of each relevant dietary constituent in the set of foods

Nutrient and food group composition data are needed to calculate HEI scores. Values for energy and the relevant nutrients may be available from package labeling or nutrient composition databases. However, determining the values for the other relevant dietary constituents means that any food mixture containing ingredients from multiple food groups (pizza, for example), must be disaggregated into component ingredients before it can be tallied appropriately. Also, if necessary, yield factors must be applied so the amounts of cooked and raw foods are on an equivalent basis. This requires a database, such as the Food Patterns Equivalents Database (FPED) (see section below on individual food intake) that translates the foods and beverages into equivalent amounts of fruits, vegetables, added sugars, and so on.

If the set of foods and beverages under consideration represents an outlet or institution that sells or serves only ready-to-eat food, databases that have been developed for individual-level analyses can be used. However, no databases are available currently to translate unprepared foods (such as raw meats and untrimmed produce) and processed but not fully prepared foods (such as cake mixes) into appropriate food group equivalents. This is a limitation for studying markets that sell these foods and beverages. If the set of foods and beverages is small, this step can be done by hand, but this is a painstaking process. Studies of the total inventories of large grocery stores will be impracticable until market-appropriate databases are available.

Step 3: Derive pertinent ratios and score each HEI component using the relevant standard

At the community food environment level, the amount of each dietary constituent is summed over all foods and beverages in the set under consideration and expressed as a ratio to total energy or, in the case of fatty acids, to total fatty acids. The resulting ratios are compared with the applicable standards for scoring (link to HEI standards).

Using the Total Fruits component as an example:

Graphic showing the mathematical formula for the described process: Dividing the sum of F for the set by the sum of E for the set gives the Assign Score for the set.

Where F = total cups of fruit in the set of foods and E = total energy content of the set of foods.

SAS macros for implementing step 3 are available.

Individual Food Intake

Data must be collected at the individual level to make inferences about groups or individuals. Most of the time, researchers are interested in making inferences about groups of individuals, or populations. A dietitian might also be interested in the HEI for clinical use to assess diet quality for an individual client. In this section, we describe uses of the HEI for population and individual intake.

Data collected at the individual level commonly use 24-hour dietary recalls, food records, or food frequency questionnaires (FFQ). NCI’s Automated Self-Administered 24-Hour (ASA24) Dietary Assessment Tool can be used to collect individual 24-hour recalls and food records. NCI’s Diet History Questionnaire is also a FFQ that can be used to collect individual dietary data.

After data collection, the intake reported by these methods must be summarized into nutrients and food groups. Data collected through 24-hour recall methodology are often coded using either the USDA's Food and Nutrient Database for Dietary Studies (FNDDS) or the University of Minnesota’s Nutrition Coordinating Center's (NCC's) Nutrition Data System for ResearchExternal Web Site Policy (NDSR; fee-based). The FNDDS and NDSR databases provide compositional information for a full array of nutrients. However, the HEI requires food group equivalents in addition to nutrients. The FNDDS links to the Food Patterns Equivalents Database (FPED), which characterizes the foods and beverages reported according to components needed to calculate the HEI. The NDSR has some food component information as well, and has developed a guide to help users create the variables needed to calculate scores using data from NDSR output filesExternal Web Site Policy.

Data collected through a FFQ that links to FNDDS can similarly be linked to the FPED and be used to estimate HEI scores. Data from FFQs that have not been linked with FNDDS would have to be appropriately coded to capture and summarize each of the dietary components required to calculate the HEI. Researchers interested in how to apply HEI scoring should see the Overview of the Methods and Calculations webpage for details regarding scoring and analysis.

Sample Studies for Population or Group Level Intake

Studies at the population or group level represent the most frequent type of HEI application. In these studies, individual persons are the units of data collection; however, inference about the HEI is made at the population level. Researchers interested in employing the HEI with data analyzed at the group level can use it to:

  • Describe the diet quality of the population overall or for subgroups defined by income, race/ethnicity, and other characteristics;
  • Examine relationships between overall diet quality and outcomes, such as mortality or incidence of a chronic disease;
  • Evaluate the impact of dietary interventions.

The HEI can be used to answer questions using individual dietary intake data to study trends in populations or groups of people. Below are example research questions that have been asked in the past and corresponding references.

Question: What was the diet quality of Americans in 2001-2002 and 2007-2008?

Reference: Guenther PM, Casavale KO, Kirkpatrick SI, Reedy J, Hiza HAB, Kuczynski K, Kahle L, Krebs-Smith SM. Diet Quality of Americans in 2001-02 and 2007-08 as Measured by the Healthy Eating Index-2010External Web Site Policy. USDA CNPP Nutrition Insight 51.

Questions: What is the relationship between diet quality and mortality risk? How does this compare across four different diet quality indices?

Reference: Reedy J, Krebs-Smith SM, Miller PE, Liese AD, Kahle LL, Park Y, Subar AF. Higher diet quality is associated with decreased risk of all-cause, cardiovascular disease, and cancer mortality among older adults. J Nutr. 2014 Jun;144(6):881-9.

Question: What is the relationship between diet quality and socioeconomic factors in disadvantaged neighborhoods in the Southeast US?

Reference: Wilcox S, Sharpe PA, Liese AD, Dunn CG, Hutto B. Socioeconomic factors associated with diet quality and meeting dietary guidelines in disadvantaged neighborhoods in the Southeast United States. Ethn Health. 2020 Nov;25(8):1115-1131.

Individual Food Intake

Individual-level dietary intake data can also be used to calculate HEI scores for an individual person, for example, within a clinical setting. However, there are caveats in interpretation of the scores at the individual level. The application of the HEI does not involve the comparison of a person's intake to their personalized dietary requirements, but rather to standards based on national recommendations. Furthermore, the recommendations upon which the HEI is based are meant to be met over time, not every day. An individual's HEI score based on a given day's intake would not necessarily reflect the score based on their usual or habitual intake, particularly for components that are episodically consumed such as whole grains.

Researchers interested in employing the HEI at the individual level can use it to:

  • Describe the diet quality of the individual person;
  • Examine relationships between overall diet quality and outcomes, such as mortality or incidence of some chronic disease.

Steps

The total foods and beverages consumed by individuals is the subject of interest at this level. Most often, researchers are interested in the usual (or long-run average) diets of groups of individuals to assess diet quality. However, sometimes information about diets of individual persons on a given day or days is the exposure of interest.

Because the HEI is most frequently applied to usual diet, it is usually calculated on the basis of the long-term average dietary intake of an individual or group of individuals. Food frequency questionnaires (FFQs) attempt to directly capture usual intake by asking respondents to estimate averages across a long time period. Other dietary assessment tools, such as 24-hour recalls (24HRs) or food records (FRs), capture short-term intakes rather than average intakes, and the resulting data are subject to day-to-day variation in diet. However, with repeat non-consecutive measurements per person, it is possible to estimate usual intake through averaging multiple 24HRs or FRs within a person. When we average on the person level, we eliminate within-person variation, such as day-to-day variability in intake, resulting in estimates that are closer to usual intake. It is also possible to apply statistical methods to isolate between-person variation from within-person variation even with a small number of days per person. These are termed “usual intake methods.”

Step 1: Identify the set of foods under consideration

Information on foods and beverages consumed by people on a day or over a longer period of time can be collected using various methods. The most commonly used methods are 24-hour recall, food record, or food frequency questionnaire. For example, HEI scores can be calculated using recall data collected in the What We Eat in America component of the National Health and Nutrition Examination Survey (NHANES) or using the Automated Self-Administered 24-hour (ASA24) Dietary Assessment Tool. Both of these sources of data can be linked to appropriate databases, including the Food and Nutrient Database for Dietary Surveys and the Food Patterns Equivalents Database. Food frequency data can also be used to calculate HEI scores if linkages to appropriate databases can be made (see step 2).

Calculating HEI scores requires information on the total diet; thus, data from brief instruments (e.g. screeners), which capture only particular aspects of the diet cannot be used for this purpose.

View a table outlining recommended methods to calculate HEI scores depending on the main purpose of the study and the dietary assessment tool utilized. For more information about selecting dietary assessment tools, see the Dietary Assessment Primer.

Step 2: Determine the amount of each relevant dietary constituent in the set of foods

Determining the amounts of each dietary constituent contained in the total quantity of foods and beverages under consideration requires linking to relevant databases. Values for energy and the relevant nutrients can be obtained from a nutrient composition database. Obtaining values for the other relevant dietary constituents requires a database that translates the foods into amounts of fruits, vegetables, lean meat, and so on. One publicly available database designed for this purpose is the Food Patterns Equivalents Database (FPED). The FPED links to the USDA's Food and Nutrient Database for Dietary Studies (FNDDS) and has been used to evaluate the US diet in relation to dietary guidance such as the USDA food patterns, which are part of the Dietary Guidelines for Americans. It translates the amounts of foods, as eaten, into cup and ounce equivalents that are consistent with the units of measure used for the HEI scoring standards. If the FPED is used, no additional steps are required to determine the amount of each food-based constituent required to calculate HEI scores.

Once the databases are identified, each food or beverage item or line item must be linked to each nutrient and food group that comprise the HEI. For each day (or relevant time period), these values are summed across all identified food groups (see HEI Scoring Illustration). The outputs of step 2 are the values for each dietary constituent that makes up the HEI score for each person for each day. The way in which these components are scored will vary dependent on the goal of the analysis and the statistical method utilized (see Step 3).

Step 3: Derive pertinent ratios and score each HEI component using the relevant standard

Although the HEI dietary constituents corresponding to each HEI component are scored according to the HEI scoring standards, the way in which person-level data are aggregated and scored, including the exact constituents used and the construction of ratios, differs in relation to the goal of the population-based analysis and hence the analytic method chosen, the dietary assessment method used, and the number of repeats of the dietary assessment measure in the case of short-term methods. The purpose of the analysis as well as the data structure must be considered in deciding upon the most appropriate method to estimate the HEI score. For more information, see the Choosing a Method webpage.