The Dietary Guidelines for Americans (DGA) provides federally developed food-based recommendations for Americans two years of age and older, designed to promote health and prevent disease. As mandated by the 1990 National Nutrition Monitoring and Related Research Act ( P.L. 101-445 ), the guidelines are to be reviewed and updated at least every five years by the Secretaries of the Department of Health and Human Services (HHS) and Agriculture (USDA). The statute requires that the DGA be based on a preponderance of scientific and medical knowledge. This report provides responses to frequently asked questions about the DGA, including the DGA development process, as well as specific recommendations contained in the 2015-2020 DGA. In accord with its statute ( P.L. 101-445 ), the DGA is based on "the preponderance of the scientific and medical knowledge which is current at the time the report is prepared." It is an evidence-based and authoritative policy document that serves as the basis for nutrition policies and programs in the United States, including the National School Lunch Program, the Supplemental Nutrition Assistance Program (SNAP), and the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). All federal dietary guidance must be consistent with the DGA. One example of how the DGA has affected public policy is through nutrition labeling. In March 2014, FDA issued two proposed rules to update the Nutrition Facts label based on recommendations contained in the 2010 DGA. More specifically, a key recommendation of the 2010 DGA was to reduce the intake of calories from added sugars, although no quantitative limit was established. In accord with the DGA recommendation, FDA issued a proposed rule that if finalized would, among other things, mandate an "added sugars" line on the Nutrition Facts label, requiring manufacturers to distinguish between added sugars and naturally occurring sugars in food. In July 2015, FDA issued a supplemental proposed rule that would require, in addition to mandatory added sugars labeling, a percent daily value (%DV) declaration for added sugars. In the initial iteration of the proposed rule, FDA proposed mandatory declaration of the amount of added sugars in a food item but not a percent daily value, citing lack of scientific evidence to substantiate such a recommendation. However, the Scientific Report of the 2015 DGAC (2015 DGAC's report) provided new evidence to support establishing a reference amount for added sugar intake. In light of this new evidence, FDA determined that establishing a percent daily value for added sugars was warranted. FDA thereby proposed that the percent daily value should be based on the recommendation that the daily intake of calories from added sugars not exceed 10% of total calories. Over the years, the DGA has evolved from an educational brochure for consumers to a policy document for policy officials, nutritionists, and nutrition educators (see Table 1 ). The eight editions of the DGA have generally contained similar recommendations regarding what constitutes a healthy diet; however, the recommendations have evolved over time to reflect the latest scientific evidence. Although the earlier editions of the DGA contained just seven guidelines, by 2005, that number had increased to 41 (23 for the general public and 18 for specific populations); despite the increase in the number of guidelines, the overarching recommendations have remained largely the same. Beginning in 2020, the DGA is expected to add recommendations for another age cohort (birth to 24 months of age), as directed by a provision in the Agricultural Act of 2014 ( P.L. 113-79 , the "Farm Bill"). The methods used for reviewing evidence to inform the DGA have also changed. In 1980, scientists from HHS (then called the Department of Health, Education, and Welfare) and USDA, along with expertise from the scientific community, were responsible for reviewing the scientific evidence and drafting the DGA. However, following the 1980 DGA's publication, various industry and scientific groups expressed concern regarding the science used to develop the recommendations. To help the departments develop the DGA policy document, a Senate Committee on Appropriations report directed that an external committee be established to review scientific evidence and recommend revisions to the 1980 DGA. In 1983, an external federal advisory committee of nine nutrition scientists was convened to review and make recommendations in a report to the Secretaries of USDA and HHS about the 1980 DGA. Following those recommendations, USDA and HHS released the 1985 DGA (the second edition), which contained almost the same recommendations as the first edition, but was more widely accepted. In 1987, a House Committee on Appropriations conference report directed HHS and USDA to "reestablish a Dietary Guidelines Advisory Group on a periodic basis. This Advisory Group will review the scientific data relevant to nutritional guidance and make recommendations on appropriate changes to the Secretaries of the Departments of Agriculture and Health and Human Services." A Dietary Guidelines Advisory Committee (DGAC) was used in developing the DGA thereafter. The 1995 DGA was the first statutorily mandated ( P.L. 101-445 ) edition of the DGA; the 1980, 1985, and 1990 editions were issued voluntarily by HHS and USDA. Another major change occurred following the 2005 DGA, when the USDA Center for Nutrition Policy and Promotion (CNPP) developed the Nutrition Evidence Library (NEL), which was then used by the 2010 DGAC to systematically review the scientific evidence to inform the development of the 2010 DGA (the NEL is discussed in greater detail in the section " What Is the Nutrition Evidence Library's Role in DGA Development? "). In the first stage of DGA development (see Figure 1 ), a DGAC is chartered following Federal Advisory Committee Act (FACA) guidelines. Within those guidelines, FACA requires that all advisory committees be strictly advisory and prohibits them from creating policy or issuing regulations. The committee is generally composed of nationally recognized experts in the fields of human nutrition, food science, and chronic disease prevention. The experts' work is solely advisory and time-limited. The DGAC provides an advisory scientific report to the Secretaries of HHS and USDA, who consider the report when writing the final DGA policy document. The 2015 DGAC was charged with examining the 2010 DGA, determining topics for which there was new scientific evidence and developing food-based recommendations that are of public health importance for Americans two years of age and older. Through the development process, the DGAC held seven public meetings to review and discuss the scientific evidence supporting the recommendations. To inform the revision of existing recommendations and suggest new guidance, the 2015 DGAC used systematic reviews, data analyses, and/or food pattern modeling analyses, as well as scientific evidence-based reports, input from guest speakers, and public comments. In addition, DGAC relied on the NEL to objectively review, evaluate, and synthesize research to answer nutrition and health questions. In 2008, CNPP established the NEL within its Evidence Analysis Library division to conduct food- and nutrition-related systematic reviews. The "state-of-the-art" systematic review (SR) methodology was developed in consultation with the Agency for Healthcare Research and Quality (AHRQ)—an agency within HHS, and the Academy of Nutrition and Dietetics (AND), and informed by the U.S. Cochrane Collaboration. NEL uses a six-step process to conduct specialized systematic reviews that inform federal nutrition policy and programs. The DGAC uses the NEL process to evaluate the evidence, which the DGAC then uses to inform the development of its Advisory Report. Where needed, NEL staff helped the DGAC carry out some steps of the NEL process. The NEL was created to ensure compliance with the Consolidated Appropriations Act of 2001 ( P.L. 106-554 , the Data Quality Act), which directed the Office of Management of Budget (OMB) to issue government-wide guidelines that "provide policy and procedural guidance to Federal agencies for ensuring and maximizing the quality, objectivity, utility, and integrity of information (including statistical information) disseminated by Federal agencies." In accordance with the first step of the NEL process (see text box), the DGAC identified research questions to be addressed through systematic reviews and developed analytic frameworks to help answer those questions. The DGAC worked with NEL staff to conduct multiple systematic reviews. Once the literature search was completed, two CNPP professionals screened the resulting articles for inclusion criteria to determine whether those articles should be included for review by the DGAC. Throughout this process, the DGAC provided oversight to ensure that studies were being appropriately included or excluded from the review and that the final list of included articles was complete and captured all research available to answer the SR questions. Key information from each study was extracted, and a risk of bias assessment (an assessment of objectivity) was performed by an NEL abstractor. NEL staff reviewed the work of abstractors, resolved inconsistencies, and generated a summary draft of the body of evidence. The DGAC reviewed this work and used it to inform its synthesis of the evidence. Although NEL staff provided oversight and assistance throughout the NEL process, the DGAC made the substantive decisions. One of the final steps in the DGAC's systematic review process was writing and grading a conclusion statement for each question, based on the body of scientific evidence evaluated. The strength of the evidence supporting each conclusion statement was graded using predetermined criteria, which assessed the quality and quantity of studies, the consistency of findings across studies, the generalizability to the population of interest, and the magnitude of the effect or public health impact. On February 15, 2015, the 2015 DGAC submitted its recommendations, as well as the scientific rationale for those recommendations, in a 571-page advisory report to the Secretaries of HHS and USDA. The Secretaries used that report, along with input from other federal agencies and public comments, to develop the final policy document, which was released on January 7, 2016.