Potential Language-Based Mechanisms of Action in Motivational Interviewing for Diet Change: Secondary Analysis of Clinical Trial Data

Motivational interviewing (MI) is a commonly employed approach to facilitating behavior change, including diet. While efficacious, the empirical basis for MI’s language-based mechanisms are in substance use, and not fully known when targeting diet change. The purpose of this study was to conduct a secondary analysis of clinical trial data to examine the language-based mechanisms of MI when targeting diet. Participants in an existing clinical trial (parents in a 10-week parent/child dyad-focused obesity prevention intervention) who received phone-based counseling that included MI from a registered dietitian (RD) were included in this study. Phone calls were recorded, and parent diet quality (Healthy Eating Index scores) and ambivalence (Change Questionnaire) were assessed pre-and post-intervention. The first session was coded using the Motivational Interviewing Skills Code Version 2.5 and analyzed sequentially to evaluate relationships between RD and participant language within sessions. Spearman correlations were used to evaluate relationships between session attributes and changes in diet and ambivalence. Results showed MI influenced communication within session as expected (e.g., when the RD used reflections focused on change talk, it was significantly more likely the participant would respond with more change talk OR = 7.55, 95% CI = 6.20–9.18, p < .01). However, use of MI was not associated with changes in diet or ambivalence (e.g., complex reflections were negatively correlated with changes in ambivalence ρ = −.31). In conclusion, counseling may not contribute to improvements in diet and ambivalence via MI-specific mechanisms. Careful consideration should be made when using MI versus other behavior change techniques when supporting diet-related change.