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2015 Dietary Guidelines Advisory Committee Nutrition Evidence Library Methodology

Systematic Review Of The Scientific Evidence: Overview

The USDA’s Nutrition Evidence Library (NEL), housed within the Center for Nutrition Policy and Promotion, was responsible for assisting the 2015 DGAC in reviewing the science and supporting development of the 2015 DGAC Report. The NEL used state-of-the-art methodology informed by the Agency for Healthcare Research and Quality (AHRQ) [1], the Cochrane Collaboration [2], the Academy of Nutrition and Dietetics (A.N.D.) [3],  and the 2011 Institute of Medicine (IOM) systematic review (SR) standards [4] to review, evaluate, and synthesize published, peer-reviewed food and nutrition research. The NEL’s rigorous, protocol-driven methodology is designed to maximize transparency, minimize bias, and ensure SRs are relevant, timely, and high quality. Using the NEL evidence-based approach enables HHS and USDA to comply with the Data Quality Act, which states that federal agencies must ensure the quality, objectivity, utility, and integrity of the information used to form federal guidance.

DGAC members developed the SR questions and worked with NEL staff to implement the SRs. The following represents overarching principles for the NEL process:
  • The DGAC made all substantive decisions required during the process
  • NEL staff provided facilitation and support to ensure that the process was implemented consistently in accordance with NEL methodology
  • NEL used document templates, which served as a starting point and were tailored to each specific review
  • When working with the DGAC, the Science Review Subcommittee provided oversight to the DGAC’s work throughout the deliberative process, ensuring that the Subcommittees used consistent and transparent approaches when reviewing the evidence from the NEL SRs.
The NEL employed a six-step SR process, which leveraged a broad range of expert inputs:
  • Step 1: Develop systematic review questions and analytic frameworks
  • Step 2: Search, screen, and select studies to review
  • Step 3: Extract data and assess the risk of bias of the research
  • Step 4: Describe and synthesize the evidence
  • Step 5: Develop conclusion statements and grade the evidence
  • Step 6: Identify research recommendations.
Each step of the process was documented to ensure transparency and reproducibility. Specific information about each review is available at , including the research questions, the related literature search protocol, literature selection decisions, an assessment of the methodological quality of each included study, evidence summary materials, evidence tables, a description of key findings, graded conclusion statements, and identification of research limitations and gaps. These steps are described below.
Once complete, the evidence portfolio including the description of evidence, evidence synthesis, conclusion, grade, and research recommendations, is used to inform the Dietary Guidelines Advisory Committee report. Information in the report was vetted by the full committee and presented at public meetings; however, more detailed supporting information on each specific systematic review is available on


[1] Methods Guide for Comparative Effectiveness Reviews. AHRQ Publication No. 10(14)-EHC063-EF. Rockville, MD: Agency for Healthcare Research and Quality; January 2014. Available from:
[2] Higgins J, Green S, editors. Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0: The Cochrane Collaboration; 2011 [updated March 2011].  Available from:
[3] American Dietetic Association. Research and Strategic Business Development. Evidence Analysis Manual Chicago, IL: American Dietetic Association; 2012 [updated January 2012].  Available from:
[4] Institute of Medicine. Finding What Works in Health Care: Standards for Systematic Reviews. Washington, DC: The National Academies Press; 2011. Available from:

Last Updated: 01/30/2015