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The USDA’s Nutrition Evidence Library

What is the Nutrition Evidence Library?

The Nutrition Evidence Library (NEL) is a systematic review entity within the USDA’s Center for Nutrition Policy and Promotion (CNPP) that uses state-of-the-art methodology to search, evaluate, and synthesize food and nutrition-related research. The NEL is staffed by Federal nutritionists and librarians with expertise in systematic review methodology. CNPP’s mission is to improve the health of Americans by developing and promoting dietary guidance that links scientific research to the nutrition needs of consumers. The NEL supports CNPP’s mission by conducting systematic reviews to inform Federal nutrition policy and programs. It is important to note that the NEL is not a repository of all food and nutrition research, nor is it a search engine or database.

What is a systematic review?

A systematic review is a research project that answers a clearly formulated question. It uses systematic and explicit methods to identify, select, and critically assess all relevant research studies, and to collect and analyze data from the studies that are included in the review.

Graphic depicting systematic review components and explained below in text.

Question mark graphic depicting a systematic review question. A systematic review question is very precise. It has a clearly defined population, intervention or exposure, comparison, and outcome. It is answerable.
X and check mark graphic depicting inclusion and exclusion of literature.
Specific criteria are defined for including and excluding literature. This helps minimize bias and ensure that the optimal literature is identified to answer the question.
Body of evidence graphic A body of evidence is carefully built by systematically and objectively extracting relevant data from all literature meeting the inclusion criteria.
A: graphic The body of evidence is synthesized and interpreted to answer the research question. Objective criteria are used to evaluate the strength or level of confidence in the evidence.

How are NEL systematic reviews conducted?

The NEL uses a six-step systematic review methodology. Its development was informed by the Agency for Healthcare Research and Quality [1], the Cochrane Collaboration [2], the Academy of Nutrition and Dietetics [3], and the 2011 Institute of Medicine systematic review standards [4]. The NEL’s state-of-the-art methodology is rigorous and protocol-driven. It is designed to maximize transparency, minimize bias, and ensure that systematic reviews are relevant, timely, and high quality. This complies with the Consolidated Appropriations Act of 2001 (Data Quality Act), which mandates that Federal agencies ensure the quality, objectivity, utility, and integrity of the information used to form Federal guidance.

Graphic depicting the NEL 6 step systematic review process.

NEL systematic reviews are completed in a collaborative manner. The NEL works with expert groups, who are convened to review the state of the science on nutrition and health. These groups include domain experts, nutrition scientists, clinicians, epidemiologists, methodologists, communicators, and/or end users of a review.

How are NEL systematic reviews used?

NEL systematic reviews help inform Federal dietary guidance. For example, a series of systematic review questions were answered by the 2010 and 2015 Dietary Guidelines Advisory Committees. These systematic reviews, along with other sources of evidence, are examined by the advisory committee and inform the advice the advisory committee provides to the Federal government on the next edition of the Dietary Guidelines. The Dietary Guidelines are the cornerstone of U.S. governmental efforts to promote health and help prevent disease through diet.

Where can I find more information about NEL systematic reviews?

NEL systematic reviews are transparent and accessible to the public. Documentation from each step of the systematic review process for all reviews completed by the NEL are published at This includes research questions, literature selection criteria (inclusion/ exclusion criteria), search strategies, lists of included and excluded studies (with rationale), assessment of the risk of bias of included studies, evidence summaries and tables, key findings, graded conclusion statements, and research recommendations.

[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: 09/27/2016