Integrating dietitians' perspectives and behavioral efficacy into food-based dietary guidelines implementation

Diet-related non-communicable diseases remain a major public health burden and diet quality is socially patterned. Food-based dietary guidelines are a core policy tool, yet they often have limited behavioral impact because recommendations can be hard to translate into everyday eating, especially in low-involvement contexts. We examined how dietitians operationalize dietary guidelines in portion-size counselling and whether guideline formats influence food intake in a real-world food environment. Study 1 surveyed 441 French dietitians about how they and their patients express portion sizes and consumption timeframes. Portion advice was most often anchored in concrete, meal-level cues (e.g., bowls, unit counts) rather than grams, and short timeframes (per meal/per day) were preferred for most foods; weekly frames were used mainly for foods to be limited and more often by less experienced practitioners. Study 2a, a randomized cafeteria field experiment (n = 336), compared three guideline graphic designs varying in processing fluency with a control message, using objective measures of calories selected and consumed (served energy and weighed leftovers). A food-group design using clear imagery and concise daily guidance reduced energy selection and intake compared with other conditions. An online post-test experiment (Study 2b, n = 201) showed that this format hits a "sweet spot" of moderated fluency: it is enriched yet easy to process. Food-based dietary guidelines may be more actionable when they mirror dietitians' meal-based language and balance visual richness with processing ease. Policy implications include involving dietitians early in guidelines' development, tailoring graphics to context-specific dietary priorities, and conducting real-world trials measuring actual food choices.