Background: This study aimed to investigate the effectiveness of mindfulness-based cognitive therapy (MBCT) as a complementary approach in patients with bulimia nervosa (BN) or binge eating disorder (BED), and to assess how the reduction of the cognitive load of words related to eating disorders (ED) could constitute an intermediate factor explaining its global efficacy. Methods: Eighty-eight women and men participated in clinical assessments upon inscription, prior to and following 8-week group MBCT. Mindfulness skills were assessed using the Five Facet Mindfulness Questionnaire (FFMQ); eating behaviours were assessed using the Three Factor Eating Questionnaire (TFEQ); comorbid pathologies were assessed using the Beck Depression Index (BDI) and the State-Trait Anxiety Inventory (STAI). The cognitive load of words associated with ED was assessed through a modified version of the Stroop colour naming task. Results: Mindfulness skills improved significantly (p<.05) after group MBCT. The improvement of TFEQ scores was accompanied by reduced levels of depressive mood and trait anxiety. The positive impact of MBCT on TFEQ score was directly related to an improvement of the performance in the Stroop task. Conclusions: MBCT represents an interesting complementary therapy for patients with either BN or BED, at least when cognitive and behavioural domains are concerned. Such efficacy seems to be mediated by the reduction of the cognitive load associated with ED stimuli, which offers a possible explanation of how MBCT could reduce binge-eating behaviours. Other studies are needed, in independent centres, to focus more directly on core symptoms and long-term outcome.