We wanted to find out how Finnish university students (n = 210) assess their ability to adopt vegetarianism and their dietary behaviour. Participants assessed 36 aspects of sustainable development with an eight-step scale. They were also invited to write free comments about their assessments. We applied Triandis’ Theory of Interpersonal Behaviour (1977). The importance of vegetarian diets was rated lower than that of any other of the 36 items assessed. However, the feasibility of vegetarian diets was considered to be relatively good. We identified two types of barriers to a vegetarian diet: social groups and habits. However, the participants were 6 percent more likely to favour a vegetarian diet than predicted by the calculated Rational Behaviour Expectancy (RBE) based on the rated importance and feasibility of vegetarian diets. The RBE of vegetarian diets was the second highest of all of the 36 items of sustainability rated. The gap between importance and behaviour was also narrowest in the case of vegetarian diets. Our study showed that Finnish university students are in the process of adopting a more sustainable way of food consumption. They need, however, supporting information about the beneficial effects of vegetarian diets on health, environment, global food security and animal welfare to overcome barriers raised by social groups and their own habits.