To address imminent concerns of global food security and agricultural sustainability, international research activities are increasingly focusing on ways of improving the food system's efficiency and effectiveness at providing nutritious food for all in an environmentally sustainable manner. A significant component of this will involve understanding and ultimately influencing people's dietary choices. However, for people-oriented intervention strategies to be effective, the gaps between existing behaviour and what is required for environmentally sustainable and healthy food choices must be specified. This paper identifies priority areas for behavioural change in relation to the types of food purchased, how they have been produced and the individual's food provisioning behaviour. In order to determine the most effective ways to influence people's consumption behaviour in light of these priority areas, the authors conducted a pilot study on a group of 163 Australians who would be expected to be early adopters of a sustainable diet. Results show that only around 1 in 10 are presently actively engaged in reducing the environmental impact of their diets in these priority areas. Hence, there is a significant need to engage many more people in sustainable dietary behaviours. Furthermore, it was found that areas where interventions are most likely to have the largest impact, based on high cost to the environment and likelihood of citizens changing their behaviour, are reducing the amount of food waste generated in the household and lowering the amount of junk food eaten.