USDA’s Nutrition Evidence Systematic Review (NESR) team is supporting the 2020 Dietary Guidelines Advisory Committee’s science-based review of specific topics and scientific questions related to nutrition and health – from birth into older adulthood.
Please visit Dietaryguidelines.gov for information about the process to update the Dietary Guidelines for Americans. You can follow along as the 2020 Dietary Guidelines Advisory Committee conducts its work by accessing the Review of the Science page. Protocols that provide details about the NESR systematic reviews that the Advisory Committee will use to answer scientific questions can be found on the topics and questions under review page.
The NESR team will be using our rigorous, protocol-driven methodology to support the 2020 Advisory Committee to conduct systematic reviews. NESR methodology for answering a systematic review question involves:
- searching for and selecting articles,
- extracting data and assessing the risk of bias of results from each included article,
- synthesizing the evidence,
- developing a conclusion statement,
- grading the evidence underlying the conclusion statement, and
- recommending future research.
NESR has previously collaborated with expert groups to conduct a number of systematic reviews on questions relevant to the 2020 Advisory Committee’s work. Therefore, when possible, NESR will identify opportunities to leverage these relevant, timely, high-quality, and transparently documented existing NESR reviews.
Our Methodology page explains more about what a systematic review is, and provides general information about the methodology we use to conduct our systematic reviews. Below is specific information about the tools we will be using to assess risk of bias and grade the evidence for systematic reviews conducted by the 2020 Advisory Committee. Additional information about NESR’s process for updating its systematic reviews is also provided.
Risk of Bias Assessment
Use of a risk of bias tool is key to ensuring that risk of bias assessments are done consistently across studies, and that the results of the assessment are transparent. NESR continuously advances its methodology to align with current best practices. For systematic reviews done to support the 2020 Dietary Guidelines Advisory Committee, the following tools will be used:
- “Cochrane risk-of-bias tool for randomized trials” (RoB 2.0) (August 2016 version) for randomized trials, including parallel group trials, cluster-randomized trials, and cross-over trials
- “Risk of Bias in Non-randomized Studies-of-Interventions” tool (ROBINS-I) for non-randomized trials
- “Risk of Bias for Nutrition Observational Studies” tool (RoB-NOS) for observational studies.
Grading the Evidence
NESR has predefined criteria that are used to evaluate and grade the strength of the evidence supporting each conclusion statement. The criteria align with best practices and are based on the following grading elements: risk of bias, consistency, directness, precision, and generalizability of the evidence, and are detailed in the NESR Grading Rubric.
Using Existing NESR Systematic Reviews
NESR will work with the 2020 Advisory Committee to identify existing NESR systematic reviews that are relevant to one or more of its systematic review questions. An existing review is determined to be relevant if it addresses a similar population, intervention and/or exposure, comparator (i.e., the alternative being compared to the intervention or exposure), and outcomes. In addition, the existing review should have used similar definitions for key terms and applied similar inclusion and exclusion criteria for selecting studies to include in the review.
If a relevant NESR systematic review is identified, NESR will work with the 2020 Advisory Committee to determine if it is timely. The Committee will consider the date range of the literature search used in the existing NESR review to determine if it is timely, or if an update is warranted. If the Committee determines that an update is warranted, NESR will conduct a literature search to identify articles published since the end of the date range used in the existing NESR review. NESR’s methodology for searching for and screening articles is described on our Methodology page. In addition, NESR will also determine whether any articles included in the existing systematic review have since been retracted.
When an existing NESR review is being used in its original form to answer a question, the Committee will carry forward the conclusion and grade from that review.
When an existing NESR review is being updated to answer a question, the Committee will consider any new evidence identified via the literature search as it relates to the conclusions of the existing review, and determine whether revisions to the original conclusion statement and/or grade are warranted.