The role of nutrition and diet in reducing the risk of chronic diseases, such as cardiovascular disease, diabetes mellitus, and certain forms of cancer, has been well documented. Concerns about the influence of dietary practices on the health status of the country have been increasingly emphasized in a number of reports and guidelines, among them the Dietary Guidelines for Americans (U.S. Department of Agriculture and U.S. Department of Health and Human Services, 1980, 1985, 1990), Healthy People 2000: National Health Promotion and Disease Prevention Objectives (U.S. Department of Health and Human Services, 1990), Surgeon General's Report on Nutrition and Health (1988), and National Research Council's report on Diet and Health (1989).
Recommended dietary practices generally include the selection of foods from a variety of food groups, particularly the grain, fruit, and vegetable groups; choice of a diet that is low in fat, saturated fat, and cholesterol; and moderate use of salt and sodium.
Much of the previous research has focused on determining which eating patterns should be recommended to the public for reducing the risk of chronic disease. Future research needs to be directed at developing measures to assess overall dietary quality. Some analytical instruments have been developed which evaluate specific dietary components, such as fat and cholesterol. Few instruments have been developed, however, which assess the overall quality of a diet.
In an effort to measure how well American diets conform to recommended healthful eating patterns, the U.S. Department of Agriculture has developed an Index, called the Healthy Eating Index. The Index was designed to provide a measure of the overall quality of an individual's diet.
The Index provides a picture of foods people are eating, the amount of variety in the diet and compliance with specific Dietary Guidelines recommendations. In designing the Index, it was not intended that the dietary components be considered individually as indicators of overall dietary quality. A score on the Index reflects a sum total of the dietary components. The following 10 dietary components were included in the Index based on different aspects of a healthful diet (figure 1):
The Index is a practical approach to measuring overall dietary quality in that it examines specific food behaviors which comprise dietary intake.
(a) Includes eggs, nuts and some legumes.
The Healthy Eating Index examines dietary intake in relation to the five major groups in the Food Guide Pyramid. A range of servings is shown for the Grain Group, Vegetable Group, Fruit Group, Milk Group, and Meat Group. The number of recommended servings depends upon an individual's caloric requirements. Recommended servings for calorie levels of 1,600, 2,200, and 2,800 are presented in Table 1.
For each of the five food group components of the Index, individuals who consumed the recommended number of servings received a maximum score of 10. A score of zero was assigned to any food group where no items from that category were consumed. Intermediate scores were calculated proportionately to the number of servings consumed. For example, if the recommended level of servings was eight and an individual consumed four servings, the component score for the individual was 5 points. A score of 7.5 points was assigned if six servings were eaten.
In developing the Index, serving recommendations from the Food Guide Pyramid were interpolated to individuals with other food energy requirements. For example, food energy RDAs for children between 1 and 3 years of age are less than 1,600 kilocalories. The recommended number of servings was retained at the minimum serving level for these children, but the serving size was scaled down to be proportionate with their energy requirements. This approach was consistent with the guidance contained in the Food Guide Pyramid. In contrast, adult males between the ages of 15 and 50 have food energy RDAs slightly greater than 2,800 kilocalories. The text of the Food Guide Pyramid provides no guidance as to how to adjust serving sizes to meet calorie levels above 2,800 kilocalories. Instead of slightly increasing serving sizes, it was decided that food portions for these individuals would be truncated at the maximum levels recommended in the Food Guide Pyramid. It should be noted, based on preliminary analysis, none of the results from the Index were shown to be significantly affected even if a slightly larger serving size were used.
Table 2 shows the serving recommendations for various age/gender categories.
Index scores for fat and saturated fat intakes were examined in proportion to total food energy (or calories).
The scores for cholesterol and sodium were each based on milligrams consumed.
Dietary variety was assessed by totaling the number of "different" foods eaten by an individual in amounts sufficient to contribute at least one-half of a serving in a food group. Similar foods were grouped together and counted only once in measuring variety. Food mixtures were broken down into their component ingredients and assigned to the relevant food groups. Index scores for variety were calculated in a manner analogous to the method used for the other Index components. Cutoff scores for variety were defined based on 3 days of recorded data. A maximum score was given if 16 or more different food items were consumed over a 3-day period. A score of zero was given if six or less different items were eaten. When based on 1 day of reported data, the cutoff scores for variety were reduced by a factor of two. Intermediate intakes were calculated proportionately.