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Let the Pyramid Guide Your Food Choices: Capturing the Total Diet Concept Part III

June 28th, 2005

By Lori Beth Dixon, Frances J. Cronin and Susan M. Krebs-Smith

STRATEGIES FOR IMPROVEMENT

Improving food guidance

Although the food guidance system succeeded in its goals of nutrient adequacy, moderation of potential excesses and usability that were set at the time, the research that led to its development is now 20 years old, and much has changed since then in our understanding of nutrition and in the demographics and eating patterns of the American public. However, the food guidance system was designed to accommodate anticipated changes in dietary recommendations over time without the need for substantial revision of the associated food guide (e.g., the Pyramid). For example, recent changes in nutrient recommendations and increasing numbers of fortified foods can be accommodated. Although the Dietary Guidelines state that supplements should not replace foods to meet usual nutrient needs, increases in the requirements of some nutrients (e.g., calcium) may require that the recommended number of servings from certain food groups be modified for certain subgroups (e.g., increase in recommended number of servings of milk products for children). Increased recommendations for other nutrients (e.g., folate) may require messages about the use of supplements by some Americans (e.g., women of child-bearing age) for whom it would be difficult to obtain the recommended amounts by diet alone.

Various food group designations, however, may deserve reconsideration. In particular, specific types of fat might receive greater or lesser emphasis, and a new typology for fruits and vegetables may be required. For example, a recent report notes convincing evidence that diets high in vegetables, particularly dark green leafy, cruciferous and alium vegetables, and/or high in fruits, particularly citrus fruits, are protective for some types of cancer. This report recommends five or more servings a day of a variety of vegetables and fruits, excluding starchy vegetables and fruits (e.g., cassava, sweet potato, potato, yam, plantain, banana). This report also recommends more than seven servings a day of a variety of other plant foods including cereals (grains), pulses (legumes), roots, tubers and plantains.

More recent data on typical portion sizes of commonly consumed foods may be helpful in quantifying the desirable number and size of servings from each group. For example, the Pyramid graphic recommends 6–11 servings of grain but does not specify how much counts as a serving. Examination of the Pyramid brochure reveals that each serving is the equivalent of only 1 slice of bread or 1/2 cup of rice or pasta, amounts that are about half the size of typical portions, if not smaller. This was the case even when the food guidance system was developed, but the developers chose to keep the suggested serving sizes consistent with previous food guides and with food labels of that time period. This decision allowed the recommended number of servings to be greater, thereby giving grains more attention in order to increase consumption. Consequently, the grains group formed the base of the Pyramid. This message requires clarification, given that grain consumption has increased without noticeable improvement in whole-grain intake.

It has been argued that the Pyramid recommendations are not the only way to achieve a nutritionally adequate diet, and that alternative schemes must be developed for vegetarians and persons who abstain from milk and milk products. In fact, the food guidance system was never meant to be limiting. The developers recognized that different guidance would be necessary for infants and very young children, vegetarians, particular ethnic groups and others with distinctly different food preferences or dietary needs. Given the increasing diversity of the U.S. population and the accompanying changes in the marketplace, the system must be adapted to different cultures and incorporate more types of foods commonly consumed by members of the rapidly growing ethnic groups in the U.S. Many alternative “pyramids” have been put forth. However, with the exception of the Puerto Rican Pyramid, none has been tested rigorously for validity and reliability against a set of stated goals and objectives based on current nutrition science. Superficial changes in the graphics with examples of ethnic or vegetarian foods will not suffice, particularly because nutrient adequacy is not verified. At the present time, national dietary data are lacking for many cultural groups and should be collected for alternative pyramids to be formally developed, tested and disseminated at the national level.

Indispensable pieces of healthful dietary patterns must be identified, and commonalities drawn across different schemes to produce universal nutrition messages. However, it is important to recognize that food guidance development is an evolutionary process. Accommodation must be made for nutrient attainment of the population, nutrient availability, diet/health recommendations and what is acceptable to people. The total diet concept, which has barely been realized, given the Pyramid graphic’s emphasis on only the major food groups, continues to have merit and should be retained and strengthened. Many of the inadequacies and imbalances in the current American diet relate to issues that were integral in the development of the food guidance system but lost in the translation to the Pyramid graphic, i.e., insufficient intakes of whole grains and dark green/deep yellow vegetables and an overabundance of added sugars and, to a lesser degree, total fat. Graphic representations of any subsequent guidance systems should prominently display these ideas.

In addition, changes in the food supply are necessary for all Americans to meet Pyramid recommendations. McNamara estimated the gaps between recommended intakes and food intakes in 1994 in order to determine changes in agriculture policy that might be needed for all consumers to meet recommended intakes. These gaps were substantial for fruits, certain subgroups of vegetables, and added sugars, and to a lesser degree, discretionary fats. For all Americans to immediately meet the corresponding Pyramid recommendations, the following changes in the food supply were estimated. The supply of fruit would have to increase by approximately two thirds. The supplies of dark green vegetables, deep yellow vegetables, and dry beans, peas and lentils would each have to triple. The supply of white potatoes and other starchy vegetables would have to decrease by about one half. The supply of added sugars would have to decline by at least one half (amounting to 21 billion pounds). The supply of added fats would have to decline by 16% (amounting to 3 billion pounds). Projecting to the year 2020, based on Census estimates for population shifts and growth, larger gaps would occur in dark green and deep yellow vegetables and in legumes. Such changes in the food supply, in combination with improved food guidance, could certainly increase the likelihood that more consumers would “Let the Pyramid guide their food choices.” The challenge is how to make these changes in the food supply.

Improving assessment

The PSDB has proved to be an extremely worthwhile tool for evaluating the diet relative to current recommendations and could aid future assessments of dietary variety, food patterns and scores. Though developed originally for use with the CSFII, it can also be used to examine data from the NHANES III with a food code linking system designed for this purpose (available at http://www-dccps.ims.nci.nih.gov/ARP/). The incorporation of tools such as the PSDB into dietary assessment software programs would broaden their capabilities tremendously. However, even the PSDB could be expanded to examine intricacies of the diet beyond those incorporated into the food guidance system. For example, it would be useful to have information on more levels of disaggregation (such as individual food commodities as well as food groups) and on more attributes of foods (such as botanical classifications for fruits and vegetables). A multilevel system with numerous attributes would increase the flexibility of the food grouping system and facilitate future analyses of the total diet accordingly.

The variety, food patterning and scoring methods provide worthwhile starting points with which to assess the total diet of Americans. Each method utilizes a different approach for condensing numerous continuous variables into a single assessment. Variety scores assess the presence/absence of food intakes, then assign a score for the number of different foods/groups; food patterns measure food group intake continuously, then truncates intake into categories; total dietary scores measure intakes of food and other dietary components continuously, then add them together. To improve upon these methods, further consideration is warranted regarding the underlying goal of the assessment.

If the goal is descriptive, such as an overall assessment of diets in relation to current guidance, scoring multiple components associated with specific dietary recommendations makes sense. However, glyphs may provide more useful information than a total diet score. A glyph is a way of visually depicting the dimensions of several variables simultaneously by constructing a common object, such as a face, and graphing each parameter to a particular feature, such as nose length or mouth shape. For example, The Interactive Healthy Eating Index, an on-line version of the HEI, allows someone to enter the foods he/she has eaten in a day. In addition to receiving a “score” for the overall quality of their diet and a “score” for each of the components in relation to the dietary recommendations, this tool also depicts a person’s diet according to building blocks of the pyramid. This pyramid glyph shows how each component of that pyramid measures up visually to the recommended amounts.

If the goal is to determine which areas of the diet are most critical, an assessment technique that discriminates, through an iterative process, which dietary factors (such as food groups) will best distinguish between “healthful” and “nonhealthful” diets would be preferred. Grain intake may contribute to the diet’s healthfulness, but grains are so ubiquitous in American diets that their measurement does not sort diets into qualitatively different groups. On the other hand, if fruit intake is the food group most likely to be absent, then fruits would discriminate among diets better than other food groups. Subgroup intakes (e.g., whole grains, dark green/deep yellow vegetables) are likely to be more discerning than the main food groups. Use of dietary supplements may further discriminate among individuals. Discussion regarding what are appropriate outcomes (e.g., nutrient adequacy, mortality, body fatness) and ways to validate these methods are necessary (e.g., use of biomarkers).

In addition to food and nutrient intakes, the concepts of variety, moderation and proportionality are important to consider. Although measures of variety and moderation have been developed and used in methods that assess the total diet, further empirical evaluation of these measures is required. Ways to assess proportionality also must be explored and tested empirically. Consistency in these measures would aid in the comparison of results across studies.

Other analytical methods, not discussed in this paper, have been used to assess the total diet. Methods such as cluster analysis, principal component/factor analysis and structural equation modeling take advantage of the correlations between dietary components to characterize diets and identify patterns. For example, cluster analysis identifies clusters of individuals with characteristic dietary patterns. Factor analysis identifies groups of dietary variables (e.g., foods listed on food records or food-frequency questionnaires), related to each other but relatively independent of other dietary variables, and calculates factor scores for each pattern for each individual. The application of other methodologies including discriminant analysis, categorization and regression tree analysis, hierarchical regression and signal detection methodology to dietary patterns is intriguing because of their potential to discriminate among interrelated variables. It is important to keep in mind that many elements of these methods are subjective. In addition, dietary patterns that result from such methods can be difficult to interpret and translate into usable dietary guidance.

Unfortunately, all methods that assess the total diet are plagued by measurement error and bias that affect dietary assessment in general. National food consumption surveys are limited by the number of days of dietary data collected; thus, they cannot provide estimates of usual intakes by individuals. Analyses based on single 24-h recalls further increase the likelihood that food and nutrient intakes of individuals, especially those in the extremes of the distributions, are misclassified, resulting in overestimation of those above or below a particular cut-off value (e.g., servings of food groups). Underreporting of energy is particularly prevalent in 24-h recalls, which may further affect whether individuals are classified as meeting or not meeting recommendations.

Efforts to counter these limitations are ongoing. For example, methods have been developed to adjust dietary data to produce nutrient estimates that more closely represent “usual intake,” provided that at least 2 d of dietary data have been collected on a subset of individuals. Use of these methods is strongly recommended when assessing the percentage of individuals whose nutrient intakes meet the dietary recommendations (e.g., percentage of individuals with saturated fat <10% of energy). Methods to adjust dietary data to produce food estimates that more closely represent “usual intake” are being explored. To increase awareness and use of these methods, software programs that incorporate these methods (e.g., C-SIDE developed by researchers at Iowa State University) must be disseminated throughout the research community with the release of national survey data. Use of doubly labeled water to validate energy intake and analytical techniques that compute energy intake in relation to basal metabolic rate using age- and gender-based equations are strategies to assess the degree of underreporting.

In conclusion, the diets of most Americans are in need of improvement. The issues surrounding dietary guidance are complex. To best assist consumers, messages must be simple and direct. This is the intent of the newly worded guideline, “Let the Pyramid guide your food choices.” However, clarification and promotion of key themes of the total diet, i.e., variety, moderation and proportionality, inherent in the food guidance system that underlies the Pyramid, are required for the guideline to have the desired effect. Improvements in methods that capture the total diet concept are warranted to best assess the diets of Americans.

Entry Filed under: General Nutrition

Let the Pyramid Guide Your Food Choices: Capturing the Total Diet Concept Part II The Secrets of Weight Loss