Lumping vs. Splitting Nutrients, Foods and Diet Patterns in Nutrition Research: Science Dialogue Mapping of Origins, Uses and Knowledge Gaps

The practices of lumping together and splitting apart foods, nutrients, and diet patterns shape the interpretation of nutritional evidence and guidance. To discuss the inherent complexity of ‘lumping’ and ‘splitting’ decisions, we held an in-person colloquium in December 2024, where we utilized dialogue mapping to summarize the discussion in real-time. Knowledgeable early-career researchers explored the contexts for lumping and splitting with the goal of beginning a conversation among the scientific community on the topic. Six key themes emerged when discussing when to lump and when to split foods, nutrients, and diet patterns: definitions and history, population heterogeneity, consumer behavior, policy and public health messaging, frameworks and categorization, and measurements and methods. The overall discussion illustrated how the rationale for lumping or splitting often diverges based on the purpose of the categorization (e.g., mechanisms, health effects, public health messaging, and food labeling), as well as data availability and the intended audience. Panelists emphasized that lumping and splitting are not inherently right or wrong, nor are they inherently a binary approach; rather, the appropriateness to lump or split depends on the purpose of the analysis, public health message, or decision. Future work is needed to operationalize lumping and splitting decisions in the field of nutrition science, and to enhance transparency in the rationale of lumping and splitting decisions.