Due to economic prosperity and population growth, consumption levels have increased particularly in affluent regions, surpassing planetary boundaries and causing significant ecological damage. Recently, researchers have advocated for a sufficiency approach, which aims to reduce consumption to essential levels only fulfilling basic needs. One example of a sufficiency behaviour is the re-use of food leftovers. Food waste reduction behaviours, in particular eating leftovers, are very exemplary measures to take to reach a sufficient lifestyle. By eating leftovers, less new food needs to be bought, bringing down the level of consumption. This thesis explores the drivers and barriers to re-using food leftovers and defines strategies for designing effective interventions. A literature review informed the creation of a initial conceptual model based on the Theory of Planned Behavior, Norm Activation Model, and other frameworks.

To evaluate if the initial model should be adjusted, interviews were conducted. These interviews were analysed using Thematic Analysis, revealed three themes: (1) difficulties of organizing, (2) doing the right thing, and the (3) ascribed value of leftover food. After the model had a final configuration, the model was tested through PLS-SEM, confirming six out of seven hypotheses and identifying five key factors: (1) attitudes, (2) personal norms, (3) skills, (4) awareness of consequences, and (5) perceived health risks. Household organization emerged as an additional critical factor from the interviews.

Design strategies were formulated for each of these six areas, focusing on positive perceptions, ethical beliefs, food safety confidence, skill improvement, and organizational support. An ideation session with design students generated six intervention concepts, which were further developed by the researcher. By addressing these key areas, the proposed interventions aim to foster sustainable behaviors and significantly reduce food waste. This research highlights the importance of rethinking food consumption and waste, promoting a culture of sufficient consumption.