Let’s Try This

The 2025-2030 Dietary Guidelines Advisory Committee (DGAC)1 is well into their evaluation of the scientific underpinnings to support the next iteration of the Dietary Guidelines for Americans. The guidelines inform a variety of federal nutrition assistance programs including the National School Lunch Program and the food packages for Women, Infants and Children, among others, and provide guidance across sectors for messaging, food innovation, and public policy. The DGAC, which is comprised of academic experts in fields critical to the guidelines, spends several years following a transparent process that will eventually deliver a report to the secretaries of the US Department of Agriculture and Department of Health & Human Services for their use in updating the Dietary Guidelines for Americans policy document. For those who have attended the meetings, it is clear that the 2025-2030 advisory process is adhering to transparency about decision-making, is substantially advancing methods for dietary pattern analysis, and continues to incorporate diversity, equity, and inclusion across the 3 streams of work.2 Yet, for a few of the topics at hand, the committee is not reaching conclusions—limited, moderate, or strong—either for lack of peer-reviewed evidence or variability in published research methods across the literature base. Those areas include the relationship between the number of eating occasions and weight, and consumption during pregnancy of low- and no-calorie sweetened beverages and gestational weight gain, among others. In several previous and the current round of evidence review, the DGAC turned to an evidence synthesis approach called “systematic review” to address the relationship between dietary patterns and cognitive outcomes. For these reviews, the DGAC crafts very specific questions that are addressed through a literature search, using the using the PICO (population, intervention, comparator, outcome) approach. In 2020, one of the DGAC questions was: “What is the relationship between dietary patterns consumed and neurocognitive health?”3 The query focused on the outcomes of cognitive decline, mild cognitive impairment, dementia, and Alzheimer’s disease. In the 2020 final report,4 the DGAC noted that in addressing this question, it faced a literature having “considerable variation in testing methods, inconsistent validity and reliability of cognitive testing methods, and differences between dietary patterns and cognitive outcomes examined.” All of this constrained their ability to draw conclusions. Interestingly, the 2025-2030 DGAC has decided to pursue a similar topic, rephrasing the question slightly: “What is the relationship between dietary patterns and risk of cognitive decline, dementia, and Alzheimer’s disease?”5 The challenge faced since 2020 is a long-standing complication. With nutrition and cognition research, the variability identified due to cognitive performance test selection and administration hinders progress—a challenge revisited about every 5 years in the literature in some form of review. It is likely that the 2020 obstacles related to dietary patterns and neurocognitive outcomes will persist as the current DGAC tackles this question. In 2023, the Institute for the Advancement of Food and Nutrition Sciences (IAFNS) organized a careful, salient review6 to understand where to go next. What do experts agree are the challenges? How can they be addressed? This may allow the field to move past this obstacle to offering the public dietary guidance for cognitive support. The reality is that one cannot ask the psychology research community to reduce variability by aligning their methods—particularly test selection—when there are many good cognitive performance tests from which to choose. However, the variety of cognitive tests available poses challenges to looking across studies and synthesizing evidence to support the development of science-based nutrition guidance. In response to this challenge, an International Expert Group7 was formed by IAFNS to innovate ways around this conundrum. The IAFNS Expert Group proposed that Retrospective Harmonization, an approach spearheaded by the Maelstrom Research Institute at McGill University,8 could be a way to leverage data from long-term prospective cohort studies that measure dietary intake and cognitive performance. It would align dietary patterns across the studies and evaluate cognitive outcomes based on aligned metrics. The idea is that by pooling individual-level data, the strength or weakness of the association becomes clearer. This Expert Group spent about a year developing the innovative methodology, now published,9 and over the course of 2024 will perform the analysis. Throughout this process, the Expert Group is also gaining a deep understanding of the nuanced differences in large study implementation (for example, various ways of collecting and reporting dietary information) that make it challenging to compare results—and usually we make comparisons based on the published literature, which can gloss over these details. Will this resolve the challenge? Will all questions about dietary patterns and cognitive outcomes be addressed and produce conclusive evidence as to which pattern is best? That is probably ambitious, but the IAFNS Expert Group has produced a pivotal building block with the potential to make progress against this apparent impasse. By trying a new approach with existing data, IAFNS and its collaborators are evaluating an innovative way around the barriers posed by the variability in available cognitive measures. Once the analysis is complete, IAFNS hopes to see new patterns of evidence that shed light on dietary guidance and cognitive support. As a scientific community, the more energy directed toward innovation and collaboration, the better the field can address today’s nutrition science challenges to advance public health.

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