In this study, we tested the effectiveness of a computer-based persuasive dialogue system designed to promote a plant-based diet. The production and consumption of meat and dairy has been shown to be a major cause of climate change and a threat to public health, bio-diversity, animal rights and human rights. A system promoting plant-based diets was developed, comprising conversational, motivational and argumentational elements. 280 participants were randomly assigned to one of four conditions, each representing a particular combination of motivational and argumentational modules. Male participants showed higher intention scores in the motivational conditions compared to the argumentation-only or control condition. Female participants scored higher overall, unaffected by condition. These results suggest that men and women are differentially sensitive to persuasive strategies regarding the adoption of a plant-based diet. It seems to be particularly worthwhile to use motivational - as opposed to merely argumentational - elements in a persuasive conversation.