The level of dietary protein is expected to be crucial for food preference because of its essential role in maintaining homeostasis. Here, we used Feeding Experimentation Devices (FED3s) to assess food preference and foraging behaviour of protein-restricted vs. control mice. Details are shown in graphical methodology; briefly, adult C57BL/6NRj mice were maintained either on protein-restricted (5% casein: PR) or non-restricted diet (20% casein: NR). Food-preference was tested in four 3-days-apart choice sessions each lasting 24h during which mice were individually placed in a cage with access to two independent FEDs delivering nutritionally distinct pellets (varying choices between 20% casein, 5% casein or sucrose) under fixed or progressive ratio. All mice, regardless of diet history, preferred pellets with relatively higher protein content (HP). However, under fixed-ratio, male PR mice consumed more HP pellets compared to male NR mice. Under progressive ratio when workload per pellet was increased for 5% casein or sucrose pellets from FED3s, male PR mice made more nose pokes than control mice but did not reach a higher breakpoint, while female PR mice did not take as many 5% casein pellets as female NR mice. Interestingly, in the light phase of all sessions, increased feeding activity was logged for male PR mice than mice in other groups. Current work is assessing patterns of switching between the two food types in each choice session that will delineate how mice prioritise choices based on their metabolic status.schematic view of the experiment design