Redesigning the Process for Establishing the Dietary Guidelines for Americans (2017) / Chapter Skim
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4 Strengthening Analyses and Advancing Methods Used
4 Strengthening Analyses and Advancing Methods Used
Pages 73-100
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From page 73... ...
These aggregate data, analyzed with the most current methodology, provide complementary information to answer different inferential questions and inform various parts of the evidence base. Properly evaluat 1 Refer to Chapter 1, Box 1-1, for an explanation of how the term DGA is used throughout this National Academies report.
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From page 74... ...
systematic reviews; (2) existing systematic reviews, meta-analyses, and reports in the literature; (3)
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From page 75... ...
committee envisions the work of the Dietary Guidelines Scientific Advisory Committee (DGSAC) to be focused on integrating results derived from multiple types of analyses (e.g., original system atic reviews; existing systematic reviews, meta- nalyses, and reports; food a pattern modeling; and descriptive data analyses)
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From page 76... ...
. As proposed in the process redesign model in Chapter 3, the NEL ought to focus on the following: • Planning and conducting systematic reviews; • Adhering to the specified protocol, including assisting in the development of systematic review questions; • Conducting the literature search and screening and selecting articles; • Abstracting data; and • Conducting a risk of bias assessment4 in individual studies.
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From page 77... ...
These steps include the systematic review protocol, a rationale for each question being asked, inclusion and exclusion criteria, and reasons for why an article was or was not included in the review.
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From page 78... ...
. Integration in this report is used to mean combining the results of systematic reviews, food pattern modeling, descriptive data analysis, and any other types of evidence to develop the DGSAC's conclusions on the total body of evidence for the DGA.
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From page 79... ...
Several best practices for systematic reviews have evolved and continue to be improved since the NEL systematic review protocol was developed. For the NEL to remain current and to continue to produce systematic reviews of the highest quality, this National Academies committee offers recommendations for the NEL to maintain state-of-the-art systematic review methods.
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by the NEL in accordance with the Federal Advisory Committee Act. In contrast, in the non-DGAC NEL process, the NEL makes key decisions relating to systematic review methodology and relies on a technical expert collaborative for domain expertise.
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From page 81... ...
In assessing the overall evidence review process, this National Academies committee explored the options for conducting systematic reviews within the NEL, as well as options outside the NEL, such as contracting out a limited number of systematic reviews to be performed by external groups. However, there are advantages of a dedicated team conducting systematic reviews like the NEL, rather than contracting to outside groups.
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From page 82... ...
Overall, this National Academies committee believes that using existing high-quality systematic reviews whenever possible maximizes limited time and resources and reduces duplication of efforts. However, it is important to recognize that existing systematic reviews may not use the same inclusion and exclusion criteria, may be out of date, or may have different outcomes (Smith et al., 2011; Whitlock et al., 2008)
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From page 83... ...
These improvements in systematic review methods will likely affect the analyses underlying the DGA. Food Pattern Modeling Food pattern modeling serves the important function of showing examples of ways individual diets can both meet energy (caloric)
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From page 84... ...
In addition to translating nutrient requirements into food combinations, the models were also used to estimate how well various combinations of foods eaten on a daily or a weekly basis, called "eating patterns," met Dietary Reference Intakes and recommendations in the DGA to promote health and prevent disease. Overall, this National Academies committee found food pattern modeling to be a useful exercise to elucidate relationships among food group nutrient profiles, nutrient goals, and energy constraints that helped inform decision making by the DGAC and the federal DGA writing team.
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From page 85... ...
Even using the relatively limited deterministic approach, food pattern modeling reveals the very small allowance for discretionary calories relative to population intakes of energy from added sugars, solid fats, and alcohol. This revelation is critically important, and yet understanding by the public of how the resulting patterns should be interpreted and followed seems to be lacking, as evidenced by the discordance between recommendations and usual intakes (Krebs-Smith et al., 2010; NCI, 2015)
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From page 86... ...
Advancing the methods used in food pattern modeling to account for the complex systems and associated pathways and variability in American diets would strengthen the accuracy of outcomes and better account for the variability in food patterns and their resulting impact to support health and prevent disease. These advancements would offer important insights into the range of nutrients and the varying combinations of "allowable" foods to stay within dietary guidelines, providing flexibility in food and taste preferences, cultural norms, and other individual factors.
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From page 87... ...
It would be helpful for data analyses to be standardized to the extent possible to allow for direct comparisons of results over time. This National Academies committee also found that the availability of data can limit the scope of the data analyses, and the expansion of data collection efforts and advancement of methods could lead to improvements in the understanding of population health and disease prevalence and trends, particularly for population subgroups.
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From page 88... ...
It would be valuable, as a first step, to document all the descriptive data analyses commonly used across previous DGACs. Quality of Dietary Data Across All Evidence Types It is important that the data informing the DGSAC Scientific Report are generated using validated and appropriate methods.
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From page 89... ...
The identification of additional biomarkers and prediction equations could improve the accuracy of dietary data. Even if biomarkers could be identified for every food and nutrient of interest, they could not replace self-reported dietary intake data, especially dietary re calls and records because dietary intake data provide complementary, contextual informaion about timing and place of meals, foods eaten in combination, and even t the fo ds themselves that biomarkers cannot differentiate.
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From page 90... ...
sideration of the quality of food intake data, future data analyses could be made more efficient by identifying questions earlier and having available data sooner, allowing for select data analyses to be performed before the first meeting of the DGSAC. It would also be helpful for selection of data and data analyses to be standardized using best practices to the extent possible to allow for direct comparisons of results over time.
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From page 91... ...
Previous DGACs have recognized the potential value and discussed the need to move toward use of systems approaches. The 2015 DGAC integrated a theoretical model that accounted for the multidimensional relationship and multiple factors influencing both dietary intake and health (see Figure 7-1 for the 2015 DGAC conceptual map)
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From page 92... ...
The model shows that, together, local context; utilization of services; and nutrition, physical activity, and stress all affect cardiovascular disease risk factor cidate and represent the actual mechanisms involved. Examples include traditional epidemiological studies that can reveal patterns and associations and attempt to control for confounding factors, such as selection and observation biases.
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Figure in Box 4-5 NOTE: CHD = coronary heart disease; CHF = congestive heart failure; CVD = cardio vascular disease; MI = myocardial infarction; PAD = peripheral arterial disease. SOURCE: Homer et al., 2008.
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It may require a few years for systems approaches to be optimally incorporated into the DGA process. Although full acceptance, understanding, and integration of systems science will require a sustained, long-term effort, some steps can be taken immediately.
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Research has suggested that excessive saturated fat intake can lead to lipid deposition within blood vessel walls, initiating a cascade of inflammatory and immune reactions resulting in coronary artery disease. However, there are multiple intermediate steps and potential modifying factors.
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Current methods need to be strengthened to better support the development of credible and trustworthy DGA. Strengthening the NEL process for conducting systematic reviews will require a multipronged approach.
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From page 97... ...
For example, ongoing collaboration with other organizations and training of NEL staff, combined with the technological infrastructure to support new systematic review methods, will need to be supported. The usefulness of food pattern modeling analyses can also be enhanced by accounting for complexity and variability in diets.
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2011. Finding what works in health care: Standards for systematic reviews.
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From page 99... ...
2008. Using existing system atic reviews in complex systematic reviews.
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