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A Series of Systematic Reviews on the Relationship Between
Dietary Patterns and Health Outcomes

 

Full Report


Executive Summary

Full Report

Background and Methodology

Systematic Review Questions

Consuming a healthy diet can help individuals achieve and maintain a healthy weight, reduce the risk of developing chronic diseases, and promote good health. Research in the field of nutrition often focuses on single nutrients, foods, and/or food groups. While looking at components of the diet individually is important to examine the effects of various aspects of the diet on health, foods and nutrients are eaten in a variety of combinations and can have interactive and potentially cumulative or confounding relationships. Thus, when developing guidance on the types of foods, beverages, and nutrients to consume, it is important to consider research on individual components of the diet, as well as research that examines dietary patterns. For the purpose of this systematic review project, a dietary pattern is defined as the quantities, proportions, variety, or combination of different foods, drinks, and nutrients (when available) in diets, and the frequency with which they are habitually consumed. As noted in the 2010 Dietary Guidelines for Americans,[1] there are several ways that a healthy diet can be achieved. The purpose of this project was to examine the relationship between dietary patterns and outcomes of public health concern.

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Background and Methodology

USDA’s Nutrition Evidence Library (NEL) conducted these systematic reviews. The NEL uses a rigorous, transparent, and reproducible methodology to conduct systematic reviews on food- and nutrition-related topics to support Federal nutrition policies and programs. The six-step process includes:
  1. Systematic review question development
  2. Literature search, screening, and selection
  3. Data extraction and quality assessment
  4. Describing the evidence and evidence synthesis
  5. Developing conclusion statements and grading the evidence
  6. Identifying research recommendations.
This NEL systematic review project was planned, organized, and guided by a NEL Systematic Review Management Team composed of Federal nutritionists trained in systematic review methodology. The NEL Systematic Review Management Team worked with a Technical Expert Collaborative (TEC) that consisted of seven national nutrition experts with knowledge in various aspects of dietary patterns. A broad range of expertise was needed to address specific issues related to the topic of dietary patterns and to guide synthesis of the body of evidence to answer the systematic review questions posed. A Stakeholder Group, which included Federal employees who represented end-users of the review and possessed varying perspectives and expertise related to dietary patterns, provided input throughout the process.

For additional information on methodology, see Chapter 3 of the full report or go to Dietary Patterns Systematic Review Project: Methodology 
 
Systematic Review Questions

At the initiation of the project, the NEL held a workshop with the TEC members, Stakeholder Group, and invited speakers to discuss the various methodologies used to assess dietary patterns and to help inform the approach for the project. Following the workshop, the TEC identified and prioritized specific systematic review questions addressing dietary patterns and outcomes of public health concern. The NEL Systematic Review Management Team helped to focus the questions on outcomes of public health importance that could potentially inform Federal nutrition policies and programs. The questions were also reviewed by the Stakeholder Group to ensure that they were relevant to policy needs.
 
The systematic review questions included in this project were organized based on (1) dietary pattern methodology and (2) health outcomes:
  • Dietary pattern methodology: Dietary patterns can be assessed in a number of ways, including numerical indices designed to gauge adherence to a particular pattern (e.g., Healthy Eating Index [HEI]) or data-driven approaches that use mathematics to empirically derive food intake patterns inherent among the study population (e.g., factor or cluster analysis) (appendix A). Dietary patterns can also be tested in trials or observed in observational studies. Because each methodology provides information about dietary patterns from a different perspective, the systematic review questions included in this project were organized based on dietary pattern assessment: (1) index analysis, (2) factor/cluster analysis, (3) reduced rank regression, and (4) other methods.
  • Health outcomes: The TEC identified three top priority outcomes for consideration: (1) body weight and obesity, (2) cardiovascular disease, and (3) type 2 diabetes. For each outcome, specific intermediate and clinical outcomes were defined (appendix B). A fourth outcome, cancer, was also identified but was not completed.
In total, 12 systematic review questions were completed in this project:

Body Weight or Risk of Obesity
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using an index or score, and body weight or risk of obesity?
  1. Are prevailing patterns of diet behavior in a population, assessed using factor or cluster analysis, related to body weight or risk of obesity?
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using reduced rank regression analysis, and measures of body weight or obesity?
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns (assessed using methods other than index/score, cluster or factor, or reduced rank regression analyses) and body weight status?
Risk of Cardiovascular Disease
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using an index or score, and risk of cardiovascular disease?
  1. Are prevailing patterns of diet behavior in a population, assessed using factor or cluster analysis, related to risk of cardiovascular disease?
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using reduced rank regression analysis, and cardiovascular disease?
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns (assessed using methods other than index/score, cluster or factor, or reduced rank regression analyses) and risk of cardiovascular disease?
Risk of Type 2 Diabetes
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using an index or score, and risk of type 2 diabetes?
  1. Are prevailing patterns of diet behavior in a population, assessed using factor or cluster analysis, related to risk of type 2 diabetes?
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using reduced rank regression analysis, and risk of type 2 diabetes?
  1. What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns (assessed using methods other than index/score, cluster or factor, or reduced rank regression analyses) and risk of type 2 diabetes?
 
[1] U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th Edition, Washington, DC: U.S. Government Printing Office, December 2010.


Last Updated: 02/04/2014