A range of behavioural phenomena such as food consumption, smoking, alcohol use, and altruism have been shown to ‘spread’ through human social networks. In particular, the spread of obesity in this manner has been identified as a contributing factor to the obesity epidemic. While specific neural reward systems such as the orbitofrontal cortex (OFC) have been implicated in social information processing, it is not well understood how more complex social factors, such as the motivation behind a social partner’s decision, are integrated into neural valuation signals that underlie one’s own preferences. Here we address this question in a human behavioural and fMRI experiment, by investigating how a social partner’s motivation influences subjects’ food choices and related neural activities. We follow the approach of Self-Determination Theory (SDT) that the reasons for undertaking a particular behaviour can be grouped into five motivational types (e.g., external vs. introjected). Accordingly, in the present experiment, participants rate motivational type and other attributes of different social partners after studying their biographical profiles. In a subsequent social food-choice task, participants observe these partners’ choices between foods varying in nutrients and sensory attributes before making a choice themselves. Preliminary data suggest that social partners’ motivational type can affect social evaluations and own food choices. Neural data will further indicate the mechanisms by which others’ motivational type can influence one’s own food-preference decisions.