BACKGROUND: The aim of the study was to identify and compare components of the COM-B (capability, opportunity, motivation and behaviour) model, that influences behaviour to modify dietary patterns in 40-55-year olds living in Northern Ireland (NI) and Italy, in order to reduce the risk of cognitive decline in later life. METHODS: This was a qualitative study examining factors influencing Mediterranean-DASH (Dietary Approaches to Stop Hypertension) Intervention for Neurodegenerative Delay (MIND) diet behaviour. This study further elaborated the COM-B components into the 14 domains of the Theoretical Domains Framework to further understand behaviour. Twenty-five Northern Irish and Italian participants were recruited onto the study, to take part in either a focus group or an interview. Participants were both male and female aged between 40 and 55 years. RESULTS: Thematic analysis revealed that the main barriers to the uptake of the MIND diet were; time, work environment (opportunity), taste preference and convenience (motivation). Culture (motivation), seasonal foods and lack of family support (opportunity) to be a barrier to the Italian sample only. The main facilitators reported were; improved health, memory, planning and organisation (motivation) and access to good quality food (opportunity). Cooking skills, knowledge (capability) and heathy work lunch (opportunity) reported as a facilitator to the Italian sample only. CONCLUSIONS: Cross-cultural differences in relation to psychosocial barriers and facilitators were found in both samples. More barriers than facilitators towards uptake of the MIND diet were found. There is a need for interventions that increase capability, opportunity, and motivation to aid behaviour change. The findings from this study will be used to design a behaviour change intervention using the subsequent steps from the Behaviour Change Wheel.