Background  Shared decision making (SDM) represents an interesting approach to optimize the impact of dietary treatment, but there is no evidence that SDM is commonly integrated into diet‐related health care.Objective  To assess the extent to which dietitians involve patients in decisions about dietary treatment.Methods  We audiotaped dietitians conducting nutritional consultations with their patients, and we transcribed the tapes verbatim. Three trained raters independently evaluated the content of the nutritional consultations using a coding frame based on the 12 items of the French‐language version of the OPTION scale, a validated and reliable third‐observer instrument designed to assess patients’ involvement by examining specific health professionals’ behaviours. Coding was facilitated by the qualitative research software NVivo 8. We assessed internal consistency with Cronbach’s alpha and inter‐rater reliability with the intraclass correlation coefficient (ICC).Results  Of the 40 dietitians eligible to participate in the study, 19 took part. We recruited one patient per participating dietitian. The overall mean OPTION score was 29 ± 8% [range, 0% (no patient involvement in the decision] to 100% [high patient involvement)]. The mean duration of consultations was 50 ± 26 min. The OPTION score was positively correlated with the duration of the consultation (r = 0.65, P < 0.01). Internal consistency and inter‐rater reliability were both good (Cronbach’s alpha = 0.72; ICC = 0.65).Conclusion  This study is the first to use a framework based on the OPTION scale to report on dietitians’ involvement of patients in decisions about patients’ dietary treatment. The results suggest that involvement is suboptimal. Interventions to increase patients’ involvement in diet‐related decision making are indicated.