Mindless eating is at the core of many ecological and social problems associated with modern nutritional behavior. Mindfulness training has been proven to be an efficient means for improving healthy nutrition. First, it enables reconnection with internal hunger and satiety cues, instead of external cues. Second, it supports making deliberate choices against unconscious eating patterns. It is less clear whether training in mindfulness can be similarly effective for sustainable nutritional habits, defined here as socially and ecologically responsible consumption behaviors over the whole consumption cycle. A controlled mixed method intervention study employed an adapted mindfulness-based intervention (MBI) to investigate such potential effects in a healthy, adult student population (n = 76/n = 11). Results from both qualitative and quantitative data indicate that the MBI exerts strong effects on mindful eating, whereas effects on sustainable nutritional behaviors are limited and only appear in the qualitative data as content concerning pre-behavioral stages of consumption, such as attitudes and intentions. First follow-up results suggest a slower process for changing nutritional behaviors toward more sustainable food choices. Based on the integrated mixed method results, we conclude that MBIs are an effective way to change unhealthy, mindless eating habits. To obtain stronger effects on sustainable nutritional behaviors, we suggest MBIs with a specific focus on sustainable nutritional behaviors and openly advertising the aim of the intervention in order to create a common intention in target groups who are looking for ways to put their altruistic intentions into practice, e.g. in sustainable consumption education programs.