A collection of consumer, health and other groups is urging the Dietary Guidelines Advisory Committee to use non-USDA systematic reviews and meta-analyses as it develops its latest version of nutrition recommendations for Americans.

Unlike previous reports, the 2020-2025 Dietary Guidelines for Americans will only use systematic reviews conducted by USDA’s Nutrition Evidence Systematic Review (NESR), formerly the Nutrition Evidence Library.

The Food and Nutrition Service said in response to questions about the matter that the DGAC “will rely on three types of evidence to answer the topics and questions: data analysis, food pattern modeling, and [NESR] systematic reviews — both existing and new.”

External reviews “and reports conducted by outside entities may be used for context and/or when designing the protocols for answering the scientific questions,” FNS said.

The reason for the exclusion is that non-NESR reviews “likely will not address the direct questions the committee seeks to answer and likely do not follow the same criteria outlined by the committee,” FNS said.

Ultimately, the DGAC will be allowed to consider outside research findings, but only those analyzed by an NESR review.

That’s a mistake, according to three dozen groups led by the American Institute for Cancer Research. In a letter to DGAC, submitted in response to a request for comments on proposed protocols to be used by the committee, the groups said they agreed that any updates to the DGAC “should reflect the latest scientific evidence.

“However, we believe that a determination to explicitly exclude the use of high-quality, scientifically sound external systematic reviews and meta-analyses will reduce the efficiency and effectiveness of the DGAC process,” they said.

Systematic reviews take a research question and attempt to answer it by analyzing and synthesizing “all relevant research studies,” according to NESR’s website. In a discussion of how NESR will conduct reviews for the DGA, NESR says, “It is important to note that all NESR reviews – existing and original – will consider all relevant research studies to answer the scientific question.”

Meta-analyses take the data from individual studies and pool them to come up with a new statistical conclusion.

The groups, which include the Center for Science in the Public Interest, Union of Concerned Scientists, and United Fresh Produce Association, said excluding outside reviews and meta-analyses “would be an unnecessary and inefficient departure from the evidence review process used by the 2015 DGAC.”

Margo Wootan

Margo Wootan, CSPI

In addition, since NESR does not conduct meta-analyses, "that will mean no meta-analyses," says Margo Wootan, vice president for nutrition at the Center for Science in the Public Interest.

The 2015 committee used outside reviews, meta-analyses or reports to answer 45% of its research questions, the groups said, and Nutrition Evidence Library reviews to answer only 27% of the questions.

A 2017 National Academy of Sciences, Engineering and Medicine report that examined the DGA process found “use of existing systematic reviews, meta-analyses, and authoritative reports from leading organizations is generally appropriate.” The NASEM committee encouraged external reviews, “with the understanding that they ought to be relevant, timely, and of high quality.”

“We acknowledge the expertise and support the methodology of the NESR team used to conduct systematic reviews,” the groups said. But the committee has a big job to do, they said, and a limited amount of time to do it — its recommendations are due by next May, with the report scheduled to become final in December. With 80 different research questions to answer, “NESR should utilize the full body of existing science and focus its time and resources most efficiently — on updates to existing high-quality systematic reviews and development of new ones on topics for which they do not already exist.”

An example of research the committee could use, the groups said, are meta-analyses on the relationship between alcohol consumption and cancer risk, which “show that alcohol increases the risk of six different types of cancer,” but the level of consumption associated with significantly increased risk differs significantly between cancer types.

“While only heavy drinking increases the risk of a number of cancers, any alcohol consumption significantly raises the risk of both breast and esophageal cancers,” the groups said. “Because the [NESR] does not conduct meta-analyses, these dose-response patterns may not be apparent if the evidence is only assessed using systematic literature reviews conducted by NESR.”

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