To describe scales that measure motivations for changing dietary behaviour, and to examine associations of these scales with current diet and dietary change.

A secondary analysis of a randomised trial of a self-help intervention to promote lower fat and higher fruit and vegetable consumption.

Participants and setting: Participants were 1205 adults selected at random from enrolees of a large Health Maintenance Organization. At baseline, data were collected on motives for changing diet, fruit and vegetable intake, fat-related dietary habits, and demographic characteristics. Participants were then randomised to receive the intervention or to receive no materials. A follow-up survey was administered at 12 months.

A majority of participants reported that it was very important to make dietary changes to feel better (72%) and to control an existing medical problem (57%), but very few (4%) were motivated by pressure from others. Factor analysis of the diet motivation items yielded two intrinsic (‘self-image’ and ‘personal health’) and one extrinsic (‘social pressure’) scales with fair internal consistency reliabilities (Cronbach's α = 0.59 to 0.68). Motivation scales were statistically significantly associated with demographic characteristics and baseline diet. For example, desire for a better self-image was a stronger motivator for changing diet among females, while personal health was more important to older persons and men (P < 0.001). Social pressure to change diet was statistically significantly associated with higher fat intake (r = 0.11) and self-image was associated with lower fat intake (r = −0.14, both P < 0.001). Motivation by social pressure and self-image were both significantly associated with greater fat reduction at 12 months post-intervention (P < 0.05).

The intrinsic and extrinsic motivation scales were weakly associated with current diet and predicted response to dietary intervention. More research is needed to better characterise and measure motives for dietary change, and to test whether tailoring interventions based on individuals' motives for dietary change would improve intervention effectiveness.