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Role and Purposes of the Dietary Guidelines for Americans: Evaluation and Findings

What foods should Americans eat to promote their health, and in what amounts should those foods be eaten? What is the scientific evidence that supports specific recommendations for dietary intake to reduce the risk of chronic disease? These questions are critically important because dietary intake has long been recognized to have a role as a key determinant of health (NRC, 1989; WHO, 2003). Some relationships between diet and health, such as under- or overconsumption of certain micronutrients, have been well established (IOM, 2001). For example, an individual whose diet lacks iron can develop iron-deficiency anemia (CDC, 1998; IOM, 2001; NRC, 1989). However, through years of scientific investigation in nutrition and health, an understanding has begun to develop that there are complex relationships between dietary intake and the risk of developing multifactorial chronic disease. Poor dietary habits have been associated with the increased prevalence of chronic diseases such as type 2 diabetes and cardiovascular disease in the United States. Likewise, poor-quality diets that result in an energy imbalance increase the risk of obesity (Erdrich et al., 2015; Hill et al., 2012; Stampfer et al., 2000). While the presence of a relationship between dietary habits and chronic disease can be identified, the precise relationship between dietary patterns and health is complex, involving dynamic interactions among physical, social, behavioral, genetic, environmental, and other determinants of health. Because of this complexity, the responses to the questions of what Americans should eat and the supporting scientific evidence are not always simple ones.

The Dietary Guidelines for Americans (DGA) is the one source that attempts to address these complicated issues. This National Academies of Sciences, Engineering, and Medicine (the National Academies) committee found it important to review the purposes and goals of the DGA to guide its deliberations about improving the current process, and presents those discussions and findings in this chapter. The chapter then articulates a set of values on which to base the committee’s assessment of the DGA process. The chapter concludes by describing how the scope of the DGA could be broadened to include all Americans and not solely healthy Americans.

ROLE OF THE DGA

To help the public better understand what eating patterns may help to reduce risk of disease, the nutrition community has long sought to offer science-based advice on food and provide practical support for its uptake. Such advice was first introduced in the United States in the late 1890s, with the themes of variety, balance, and moderation. In the following decades, numerous food guides were published from a variety of sources; most were similar and identified a range of 7 to 10 food groups. In the 1950s, the U.S. Department of Agriculture (USDA) simplified its “Basic Seven” food groups to the “Basic Four,” with the focus of being a “foundation diet”—a diet meeting the major portion of calories and nutrients needed, assuming that people would supplement their diets for the remainder of the calories and nutrients. In the 1970s, quantitative goals for intakes were set to make food guides more directive, but these efforts led to controversy in the field, as the diets needed to meet the goals differed greatly from the usual food patterns of average Americans. For example, in 1977, the U.S. Senate Select Committee on Nutrition and Human Needs recommended a set of dietary goals for Americans, calling for the public to expend as much or more energy (kcals) as it consumes and suggesting nutrient- and food-based targets. When those goals were publicly released, industry and the scientific community questioned whether the recommendations could be supported by available science. The general public was left confused, suggesting the need for a single, authoritative, and consistent set of advice on diet and health from the federal agencies. As a result, USDA and the U.S. Department of Health and Human Services (HHS) developed the DGA, which provide the general public with a single set of food-based advice (Welsh et al., 1992).¹

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¹ Per the National Nutrition Monitoring and Related Research Act of 1990, “At least every five years the Secretaries [of USDA and HHS] shall publish a report entitled ‘Dietary Guidelines for Americans.’ Each report shall contain nutritional and dietary information and guidelines for the general public, and shall be promoted by each Federal agency in carrying out any Federal food, nutrition, or health program.” Refer to Chapter 1, Box 1-1, for an explanation of how the term DGA is used throughout this National Academies report.

The DGA serve as the primary federal source of consistent, evidence-based general information on diet and nutrition. In this role, the DGA have the potential to empower Americans to make informed decisions about what and how much they eat to improve health and reduce the risk of chronic disease. To make the DGA attainable by the general population and subpopulations, the DGA have been designed to have an important role in federal food policies and programs. As the basis for the types and composition of food provided in government food programs, the DGA can be used as a basis for the development of and access to more healthful products by food manufacturers, supermarkets, restaurants and food service operations, and other segments of the food sector. The DGA have the potential to improve population health through enhanced adherence to the DGA recommendations by individuals and use of the DGA by the private and public sectors.

Despite this potential, less than 10 percent of Americans consume a diet fully consistent with the DGA (HHS/USDA, 2015; Krebs-Smith et al., 2010; Wilson et al., 2016). For example, many consume greater quantities of solid fats, added sugars, alcoholic beverages, and sodium than recommended. Why Americans fail to adhere to the DGA is uncertain. Multiple factors have been reported as causes for the lack of adoption of the DGA, including cost, taste, challenges with identifying practical strategies to bring about change, foods being unavailable, concern over the healthfulness of the guideline diets, and difficulty in making dietary change (Nicklas et al., 2013). Other causes may include the societal context driving eating patterns and people simply not being aware of the DGA recommendations. Confusion may exist as a result of the presence of numerous dietary guidelines or the perception that dietary guidelines are constantly evolving (e.g., recommendations on consumption of eggs have changed). Another potential reason for lack of adherence is that the public has “lost faith” in the DGA (U.S. Congress, House of Representatives, Committee on Agriculture, 2015). As raised by members of Congress, if the credibility of the guidelines is low or questionable, adherence to the guidelines is likely to be limited (U.S. Congress, House of Representatives, Committee on Agriculture, 2015).

Many of the potential reasons for lack of adherence to the DGA recommendations require review of the environmental and behavioral aspects of the food system and food consumption. However, questions related to the credibility and trustworthiness of the DGA recommendations can be addressed through review of the process by which they are developed. The adoption and widespread translation of the DGA require that they be universally viewed as valid, evidence based, and free of bias and conflicts of interest to the extent possible. This report provides recommended changes to the DGA process to reduce and manage sources of bias and

conflicts of interest, improve timely opportunities for engagement by all interested parties, enhance transparency, and strengthen the science base of the process. Redesigning the process is an essential first step, but evaluation will also be needed to understand whether the public does in fact trust the process and, in the long-term, whether adherence to the DGA recommendations actually improves.

CLARIFYING THE PURPOSES OF THE DGA

The purpose and uses of the DGA have undergone subtle changes over their more than 30-year history (see Table 5-2 for a detailed evolution of the DGA).² This evolution has led to some confusion about what and for whom the DGA are intended. Indeed, upon review of materials related to the 2015–2020 DGA Policy Report, more than 10 different statements can be found describing the purposes, goals, and intended audiences for the DGA. While many of these statements overlap, some are conflicting. Some of the confusion about the purposes and audiences of the DGA stems from the multiple outputs of the process used to derive the DGA, such as the Dietary Guidelines Advisory Committee (DGAC) Scientific Report and the DGA Policy Report (see Table 2-1).

The purposes of the DGA are also different from those of the Dietary Reference Intakes (DRI, described in more detail in Chapter 7 and Appendix E), which focus on recommendations for specific nutrients. The DGA, by contrast, are food-based recommendations. To promote clarity in understanding the purposes and audiences of the various products of the DGA process, this National Academies committee proposes specific functions and ultimate recipients for each product of the process used to update the DGA (see Table 2-1).

Some materials currently exist that appear to be consumer oriented but are developed for use by health professionals. Disseminations such as Choose MyPlate and SuperTracker are important tools. These Internet-based tools are useful, but they do not necessarily reach everyone that could benefit from following the DGA. This National Academies committee believes the DGA recommendations themselves need to be their own separate, consumer-oriented publication—similar to the brochure form that was produced prior to 2005—to clearly articulate the DGA recommendations to the general public. Both the proposed brochure and DGA disseminations will be important to communicate the guidelines to the public.

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²Table 5-2 shows how the audience and format of the DGA have changed over time. Originally, the DGA were published as a brochure for consumers; the DGA are now lengthy reports written for policy officials, nutritionists, and nutrition educators.

TABLE 2-1 Delineating the Functions and Audiences of Products Related to the DGA Process

NOTE: Bold text indicates a proposed addition.

To achieve the promise of the DGA, this National Academies committee proposes that the DGA adhere to a consistent set of purposes and goals across cycles, based on the National Nutrition Monitoring and Related Research Act (such as those seen in Box 2-1).

FINDINGS ABOUT THE PROCESS TO UPDATE THE DGA

The process to update the DGA has evolved over time to account for advances in nutrition science. However, this National Academies committee found the entire DGA process has not been comprehensively reconsidered in a manner that effectively allows it to adapt to change while also protecting the integrity of the process. For example, to keep up to date with improvements in the evidence base, the Nutrition Evidence Library was introduced to conduct original systematic reviews. Although the ability to consider original systematic reviews has led to improvements in the DGA, the use of original systematic reviews has also resulted in questions about the validity of the evidence assessments. The following sections summarize the key findings of this National Academies committee as they relate to process cycle time and component tasks, transparency, and participation. A more complete discussion of the process and this National Academies committee’s findings and conclusions can be found in Part II of this report.

Opportunities for Improving Cycle Time and Component Tasks

The DGA have traditionally followed a paradigm where the entire DGA are reviewed with each 5-year cycle. However, similar findings and messages have been repeated over the history of the DGA. Moreover, several of the DGA recommendations have been quite stable over a number of cycles (see Appendix D), bringing into question the utility and effectiveness of reviewing large portions of the entire body of literature every cycle.

In addition to the 5-year cycle time specified in the National Nutrition Monitoring and Related Research Act, the scientific review conducted by the DGAC is limited to a 2-year term by the Federal Advisory Committee Act.³ Component tasks related to the DGAC—including identifying topics, requesting analyses be conducted, evaluating the science, and developing conclusions—all need to be completed within the 2-year term limit in order to inform the development of the DGA Policy Report. As described in Chapter 5, the 2015 DGAC, which followed a process similar to that of the 2005 and 2010 DGACs, spent one-third of its time (8 out of 24 months) devoted to preliminary work such as understanding the work of the previous DGAC, identifying topics and questions for review, and then waiting for the scientific assessments to be completed. This National Academies committee believes having to finalize all these component tasks in 2 years, while also synthesizing and interpreting the evidence, challenges the quality of the DGA updates and constrains opportunities for greater stakeholder participation. The current process would benefit from a redesign that increases time available for stakeholder engagement, evidence assessment, and deliberations, while being responsive to change.

Opportunities for Increased Transparency

Transparency is an important attribute of trustworthy guidelines. The current process to update the DGA can be made more transparent. The entire process has not been clearly described, particularly steps related to decision making. For example, how DGAC members and consultants are selected has not been made clear. How federal DGA writing team members are selected or what standards it uses when developing the DGA recommendations is not thoroughly documented. Additionally, how the writing team interpreted the DGAC Scientific Report and why some conclusions were modified or omitted when developing the DGA Policy Report has also not been clearly described. This lack of transparency

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³ Per the Federal Advisory Committee Act, discretionary federal advisory committees are limited to 2-year terms, but may be permitted to disband sooner if the work of the committee is complete.

resulted in suggestions that the process is being inappropriately influenced by the food sector, lobbyists, faddism, and the federal government (see Chapter 1). Standards for guideline development now include high levels of transparency and are increasingly being adopted, for example, by the U.S. Preventive Services Task Force and the World Health Organization (Brouwers, 2010; Guyatt et al., 2008; HHS, 2014; IOM, 2011; Schünemann et al., 2013, 2014; WHO, 2017). The current process also does not clearly separate the roles of selecting topics, conducting analyses, interpreting the evidence, and drawing conclusions. This confluence of roles adds to the appearance that decisions may not be made independently throughout the DGA process.

Additionally, the secretaries have directed each new cycle of the DGA to begin with a DGAC to evaluate the previous version of the DGAC Scientific Report and DGA Policy Report to determine whether updates of previous conclusions are required. Thereby, each successive DGAC appears to have determined its own direction of inquiry and review in the absence of an explicit, overarching strategic plan that spans multiple cycles of the DGA. As a result, the transparency of the process to evaluate and translate the science is suboptimized. The priorities for the scope and shape of future DGA have also not been consistent or predictable. The lack of clear documentation and disclosure has led to concerns about the impartiality of the decisions being made.

Opportunities for Increased Participation

Timely, proactive stakeholder engagement is another attribute of effective guidelines. The current process offers several opportunities for stakeholder engagement such as the requests for nominations for DGAC members and comments regarding the DGAC Scientific Report (see Chapter 5). USDA and HHS have invited written comments throughout the duration of the DGAC’s deliberative process. The public also has had opportunities to make suggestions orally to the DGAC and the federal staff developing the DGA. However, more opportunities for public participation exist that may add value and credibility to the process. For example, the public can be provided venues or mechanisms to participate at key steps in the process, such as topic identification and question development.

These findings suggest that a number of opportunities for improvement exist and need to be acted upon to help enhance the integrity of the process to update the DGA, suggesting the need for the process to be redesigned.

VALUES TO ENHANCE THE INTEGRITY OF THE PROCESS OF DEVELOPING THE DGA

In response to its charge, this National Academies committee envisions an updated, redesigned DGA process. The redesigned process would clarify the audiences and purposes of the various reports that result from the DGA process, improve efficiencies, and introduce advances in scientific methods used. Together, these changes are expected to improve the integrity of the process for updating the DGA.

In its first report, this National Academies committee identified five values for improving the integrity of the process used to select the members of the DGAC:

1. Enhance transparency.
2. Manage biases and conflicts of interest.
3. Promote diversity of expertise and experience.
4. Support a deliberative process.
5. Adopt state-of-the-art processes and methods (NASEM, 2017).

This National Academies committee believes these same values remain applicable to the full process used to update the DGA. If operationalized, the values can collectively address the aforementioned opportunities for improvement. The five values have been adapted to apply to the redesign of the DGA process and are described in the following sections.

Emanating from these values and the proposed redesign is the concept that a more flexible process can result in more efficient use of resources and a minimization of duplication of efforts, particularly as the needs and topics of the DGA evolve (see Box 2-2).

Enhancing Transparency

To produce trustworthy DGA and provide assurances that decisions are not tainted by bias or undue influence, the process to produce the DGA must be transparent. A fundamental value of the DGA process redesign is to enhance transparency of the process. It is a multilayered process that needs to be transparent at each level, requiring each step of the process be documented and updated, and that such documentation be readily available to the public. Documentation of the steps used to evaluate the scientific evidence and to reach consensus on the DGA would help the public to more thoroughly understand the complexities of the processes needed to update the DGA and potentially lead to greater credibility in the decisions made.

Managing Biases and Conflicts of Interest to Promote Independence in Decision Making

An effective process redesign needs to ensure independence in decision making. The different steps of the process—topic identification, scientific review, development of DGA recommendations—are unique and necessarily involve multiple actors representing different areas of expertise and experience. The process redesign will need to align

the roles and responsibilities needed at each step of the process with appropriate experts involved in decision making. As discussed in this National Academies committee’s first report, the biases of called-upon experts should be balanced among a broad representation of perspectives. Actual and/or perceived conflicts of interest—both financial and nonfinancial—will need to be eliminated to the extent possible or their effects be minimized and managed (see Box 2-3).

Promoting Diversity of Participation, Expertise, and Experience

Trustworthiness of the process can also be enhanced by increasing participation. This National Academies committee believes a diversity of perspectives (i.e., from a broad range of expertise and experience) needs to be represented and considered at appropriate times throughout the process by which the DGA are produced. Opportunities for meaningful public participation and engagement at each step of the process (i.e., topic selection, scientific review, development of DGA recommendations) are essential. In the steps of the process where public participation would be inappropriate, such as decision making for the DGA recommendations themselves, it will be critical for the agencies responsible for the DGA to explain to the public why key decisions were made.

Encouraging participation from stakeholders who represent a wide variety of perspectives, including the public, is also critical to fostering diversity. However, it is important to recognize that not every possible viewpoint has to be or can be represented. In this report, the term stakeholder is used to mean active partners in the process to update the DGA, including the general public, academia and researchers, advocacy groups, professional organizations, the food sector,⁴ and federal agencies. Different stakeholders have unique roles in advancing the goals of the DGA. For example, health professionals and federal agencies can help review the utility of resources developed to disseminate the DGA prior to their publication. The food sector can help highlight the implications of specific DGA recommendations on the food supply or production.

The transfer of knowledge from science-based recommendations into actionable guidance that may be adopted by the general public can be challenging. An intentional effort to do so is warranted and should be guided by models that deploy proven processes. In the case of the Ottawa Model, the process to transfer research recommendations into practical guidance follows six steps: (1) setting the stage; (2) specifying the innovation; (3) assessing the innovation, potential adopters, and the environment

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⁴ In this report, the term food sector is used to refer to food manufacturers, retailers, food service, and restaurants.

for barriers and facilitators; (4) selecting and monitoring the knowledge translation strategies; (5) monitoring innovation adoption; and (6) evaluating outcomes of the innovation (NCCMT, 2010). Although a more in-depth discussion of knowledge transfer is beyond the scope of this report, this National Academies committee believes there is significant value in considering a formal approach to translate and transfer knowledge into practical guidance for the public.

Encouraging adoption of the DGA could be facilitated by including topics of importance to the general public through established methods such as trend analysis of Internet searches and social media (e.g., Google trends, Twitter analytics, news media sources) and surveys. Once true trends are identified, analytical techniques such as data mining and geospatial information mapping can be used to determine what topics are of interest to the general public, as well as to subpopulations. Surveys could also be conducted to identify what nutrition topics are of public interest. To develop guidelines that people can follow, it will be important to turn the DGA recommendations into practical advice to help consumers make decisions in the marketplace.

While broad participation in the process should be proactively sought, participation needs to be incorporated thoughtfully. For example, in addition to specific calls for comments regarding DGAC membership, participation also ought to be incorporated in other steps of the process, such as topic identification. The use of technical experts throughout the process is another way to engage with interested parties. Invited experts could be members of or called upon by a federal advisory committee to share ideas or respond to concepts, or serve as peer reviewers. As discussed in this National Academies committee’s first report, care will need to be taken to account for potential biases and conflicts of interest. All stakeholders could provide input into the process; however, only experts as appointed by the secretaries of USDA and HHS ought to be involved in decision-making processes throughout the development of the DGA, including the DGA Policy Report.

Supporting a More Deliberative Process

Another value of the process redesign is to support a more deliberative approach that is adaptive to dynamic shifts in the system in which it operates. Characteristics of a deliberative process include supporting adaptability, continuity, and continuous learning. The redesign seeks to adopt a more deliberative process by obtaining input from multiple stakeholders, as discussed above, and by adopting a process that is adaptable to changing circumstances. Although the present process for establishing the DGA results in a report once in every 5-year cycle, the committee

believes that a more continuous model, with deliberations by different constituent committees during the cycle, would be advantageous. This redesign would increase continuity from cycle to cycle and would incorporate continuous quality improvement into the process. Deliberations would go on at various stages of the process, assuring greater input from experts, generalists, stakeholders, and the public at large.

Increasing Adaptability and Flexibility

One characteristic of a deliberative process to update the DGA is responsiveness to the needs of stakeholders, including the nutrition community, technical experts, and the public. To that end, the process needs to be flexible enough to recognize the rapidly changing environment of diet and health, and the process needs to progressively move closer to elucidating the complex systems involved. As a result, the DGA process could shift from operating as a deterministic structure to one that has the agility to adapt to change and address high-priority topics in detail.

After review and discussion, this National Academies committee believes that the secretaries of USDA and HHS have flexibility in interpreting the National Nutrition Monitoring and Related Research Act and are able to adopt a more flexible process for reviewing, updating, and publishing the DGA. Given how the purpose and audience of the DGA have changed over time, the breadth and content of each required report ought to be interpreted such that not all topics require a detailed review every 5 years. Brief updates of evidence may be conducted, or a particular DGA recommendation could be extended and continued without a new in-depth review, unless ongoing surveillance (as described in Chapters 4 and 6) suggests that specific topics need to be restudied. Continually updating the DGA recommendations will necessarily be a time-intensive, difficult process to conduct, but precedent has been set for guidelines having an “expiration date” or sunset clause (APA, 2015; Graham and Harrison, 2005; IOM, 2011). For DGA recommendations for which the strength of evidence is very strong, the expiration date could be longer than those for which the evidence is rated as moderate. Resulting changes would be made with consideration of the full set of DGA recommendations.

In a redesigned process where only portions of the DGA are updated in each cycle, only those topics with enough data to generate a full review would be considered for inclusion in the next DGA cycle, which would also allow for a broader range of topics to be considered. Topics for review could include those that (1) have been reviewed previously and a body of new evidence now exists; (2) have met their expiration date; or (3) are new and being considered for inclusion in the DGA for the first time. The

resulting process would likely be more resource efficient than the current process. Additionally, for end users, a more flexible process might produce a DGA that is easier to implement, by virtue of limiting the recommendations to changes from the previous edition.

Improving Continuity

To facilitate a deliberative process, the DGA cycles need to be considered as a continuous activity to foster learning across cycles. In this way, the body of evidence describing the relationship between diet and health can progressively grow, instead of providing static recommendations that are relevant only for a given 5-year cycle or leaving the impression with the general public that recommendations change frequently. By building on identified gaps in knowledge between DGA cycles to develop and prioritize questions for consideration, the effectiveness, efficiency, and transparency of the process can be improved.

Explicitly integrating a process linkage between DGA cycles entails making large structural changes, and must be approached deliberately to minimize unintended consequences. To guide a restructuring effort, this National Academies committee believes continuity needs to be integral to the DGA process to develop a more strategic approach to accomplish the goals and vision of the DGA. Development of such an approach can help provide additional opportunities for stakeholder participation and increase transparency of what is included in the DGAC Scientific Report and the DGA Policy Report, and can shape the scope of future DGA in more predictable ways.

Assuring Continuous Learning

The DGA process itself needs to evolve and improve dynamically in order to achieve its goals. This is a consequence of the speed of change in science and evidence generation, as well as continuous introduction of new information and communication technologies. A continuous quality improvement system needs to be developed and implemented to meet this requirement, and was recommended previously in Chapter 5 of this National Academies committee’s first report in the context of improving the subprocess for selecting the DGAC committee: “Recommendation 4. The secretaries of USDA and HHS should adopt a system for continuous process improvement to enhance outcomes and performance of the Dietary Guidelines Advisory Committee selection process” (NASEM, 2017, p. 92). That recommendation also applies to the process to update the DGA.

Continuous quality improvement requires a long-term commitment and the resources to appropriately collect and evaluate data, report back

to relevant stakeholders, and engage with them in iterative cycles of improvement. Data for evaluating the overall process could be collected to measure the level and nature of stakeholder participation, as well as levels of satisfaction among experts involved with developing the DGA after implementation of the process redesign. Transparent and participatory continuous quality improvement can also help improve the integrity of the DGA process.

To best assess the growth and the adequacy of the process to update the DGA, the secretaries of USDA and HHS will need to implement a monitoring and evaluation plan as soon as possible. The term monitor as used here generally refers to a set of activities to systematically track progress of the implementation of a process. Ongoing monitoring of the short- and long-term adoption and effect of the DGA can help inform future updates. For example, knowing the rates of adherence to the DGA, the reasons for nonadherence, and related trends by populations could be helpful in being able to target how messages are crafted and disseminated in future cycles. Data from market trends databases and consumer behavior and values surveys could also be considered. Progress in filling research gaps through federal research initiatives such as the validation of chronic disease biomarkers, among others, also could be monitored to help advance the state of the evidence.

Evaluations build on monitoring activities and focus on analyzing the overall process and its effect. Understanding the effect of the DGA on federal food assistance and nutrition education and outreach programs will be important for assessing the overall effectiveness and relevance of the DGA. For example, have changes in adherence been observed in those enrolled in the WIC program and children in the school foods program? Other ways to measure adherence to the DGA include reviewing food intakes. The National Health and Nutrition Examination Survey estimates usual dietary distribution intakes of individual nutrients, foods, and food groups included in the DGA; these analyses are routinely conducted and have been provided to the DGAC in the past as described in Chapter 6. One way to assess adherence to the entire set of DGA recommendations is through the Healthy Eating Index, which is designed to measure conformance to the DGA through survey data and has been updated after each of the past three DGA cycles. Healthy Eating Index scores and component scores can be used to identify different patterns of eating. These scores could be applied not only at the level of individual diets but also to foods consumed in the marketplace or restaurants, or even the national food supply.

In the long term, the effectiveness and efficiency of the process will need to be assessed. For example, it was hypothesized that introducing strategic planning and flexibility into the process would simplify each successive DGA cycle. Determining whether the costs and time associated

with implementing the process are appropriate will also be a valuable indicator of the success of the process.

Adopting State-of-the-Art Processes and Methods to Maximize Scientific Rigor

Scientific disciplines evolve and adapt with the emergence of new evidence. To maximize scientific rigor, the process by which the science is reviewed needs to be strengthened by using (1) validated, standardized processes and methods, as available; and (2) the most up-to-date data from nutrition monitoring surveys, food databases, and disease surveillance systems. Processes and actions ought to be based on the best available evidence, requiring that the quality of the current types of evidence (i.e., systematic reviews, food pattern modeling, and data analysis) be continuously improved. In situations where data are owned by the food sector, the companies could be sourced for inclusion. Chapter 4 offers specific suggestions for strengthening these analyses.

An emerging scientific discipline and suite of methods that can be applied in nutrition is systems science (Lee et al., 2017). Systems approaches and methods aim at elucidating the interactions and pathways (e.g., biological, behavioral, social, and environmental) involved in complex relationships, such as the relationship between diet and health. Systems methods can elucidate the dynamic behavior of a system and can help generate hypotheses to explain why a system acts in certain ways. Systems science has been successfully used in other fields such as weather and transportation, and there have been calls to use systems science to address nutrition-related problems such as obesity (Maglio et al., 2014). Although the integration of systems approaches in the field of nutrition is still in its infancy, these approaches hold a lot of promise. With respect to the DGA, establishing and modeling the multisectoral relationships and pathways between diet and health has the potential to strengthen the science base of the DGA recommendations and can identify important gaps that require further investigation. Systems methods can also help identify and explain the probable limitations of the DGA and illustrate what effect can be expected from dietary changes in alternative scenarios.

The DGA can play a key role in advancing the understanding of the role of diet within the larger system of factors that affect health. However, understanding the precise role of each DGA recommendation in improving health and reducing chronic disease risk is a long-term iterative process that will take multiple DGA cycles to complete, but over time will lead to increasing clarity. When systems approaches are fully integrated into the DGA process, systems maps and models can continue to evolve to reflect new evidence and move toward better representing the mecha-

nisms and pathways involved. Integrating systems approaches into the evidence review process will be useful to advance the understanding of the potential contribution and limits of the DGA to improving health and reducing the risk of chronic disease. Additionally, supporting and conducting studies to evaluate and test the nature of the DGA’s contribution is an important component of an effective continually improving process. It is the belief of this National Academies committee that systems approaches could develop into an essential tool for understanding the many dynamic interactions and mechanisms by which diet affects health. These tools could be applied with a goal of improving health. Further discussion regarding the actual methods of systems science can be found in Chapter 4.

BROADENING THE SCOPE OF THE DGA

A fundamental change is required such that future cycles of the DGA focus on the general public across the entire life span, and not just healthy Americans ages 2 years and older. The Agricultural Act of 2014 mandates that the 2020–2025 DGA include considerations for pregnant women and children from birth to 24 months (see Chapter 5 for more details). Given the prevalence of chronic disease and risk for chronic disease in the population, this National Academies committee believes it will also be essential for the DGA Policy Report to include all Americans whose health can benefit by improving their diet based on the scientific evidence. Without these changes, present and future dietary guidance will not be applicable to a large majority of the general population.

Numerous organizations including the National Institutes of Health and professional societies have developed and endorsed their own population- or disease-specific dietary guidelines. The DGA are not designed to adjudicate among the various dietary guidelines, but confusion regarding these multiple sets of guidelines could be reduced. One way to help the public understand which set of dietary guidelines to follow would be to identify areas of consistency among the various guidelines that are developed in a manner consistent with the methods used in the DGA; these other guidelines could be referred to in the DGA Policy Report.

Specific to those who have an established disease, making good dietary choices is part of managing disease and controlling chronic disease risk factors. In some cases, disease prevention or treatment is primarily dietary, while in others diet is part of a more complex plan of management. Whereas a movement toward encompassing persons with chronic disease as the intended audience for the DGA is at present aspirational, one example with strong evidence is the Dietary Approaches to Stop Hypertension (DASH) dietary pattern. The DASH dietary pattern is

prominently recommended as part of a healthful eating pattern for those with hypertension and prehypertension (NIH, 2015) and is consistent with the DGA recommendations. Such high standards of evidence are needed to be able to address disease management. As the evidence base increases, opportunities need to be capitalized on to provide dietary recommendations that address management of other diseases.

If the focus of the DGA is shifted to include the general public, such a shift will likely have many implications for the process of establishing the DGA, the DGA themselves, as well as associated eating patterns. For example, an eating pattern for weight loss might need to emphasize where calories could be reduced without compromising the nutritional quality of the diet. A diet for secondary prevention of heart disease might be based on an eating pattern recommended for the general public, but include specific modifications known to decrease the risk of cardiac events in those individuals with heart disease. Providing more information on eating patterns could help enable health care providers in their use of the DGA. Additionally, broadening the scope of the DGA will bring challenges and likely require new approaches to evaluate the evidence. For instance, research on the effect of diet exposures in pregnancy and early life on long-term disease risk is a relatively new field predominated by observational studies. New approaches to evaluation of such data need to be developed. The DGA always needs to be based on the best available evidence using a variety of methods (see Chapter 4 for further discussion). The process redesign will provide opportunities to expand the methodological approaches to develop the DGA to include broader groups of people with a range of physiological needs, metabolic health, and chronic disease states.

CONCLUSION

The DGA can play a role in improving health and reducing the risk of chronic disease in America, and can greatly affect the foods and combinations of foods that people consume. However, the effect of the DGA will be limited if they do not apply to the general population and if the public questions the credibility of the process and the ultimate DGA recommendations. To develop a trustworthy DGA, the process needs to be redesigned. USDA and HHS have the opportunity to adopt a more flexible, continuous process that engages a broad stakeholder community in the DGA process. It will be imperative for the process to enhance transparency, manage biases and conflicts of interest to promote independent decision making, promote diversity of expertise and experience, support a deliberative process, and adopt state-of-the-art processes and methods to maximize scientific rigor. A process redesign model is proposed in Chapter 3.

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