Dynamics of feeding behaviour and meal patterning in protein-restricted mice

Of the three dietary macronutrients, protein plays an especially pivotal role in physiological functions. Nevertheless, the behavioural control of protein intake is poorly understood. In this study, we used Feeding Experimentation Devices (FED3s) to examine the structure of ingestive behaviour in mice given access to diets varying in protein content. Adult C57BL/6NRj mice were contact-housed in pairs in custom-made cages with perforated dividers, each having access to an individual FED3 unit. Mice were given ad libitum access to either 20 mg control, non-restricted (NR) pellets (20% casein) or 20 mg protein-restricted (PR) pellets (5% casein) from FED3s on free-feeding mode. Each pellet retrieval event was timestamped ~24 h/day. All mice experienced both diets for 7 days with order of diet presentation counterbalanced (i.e., NR[->]PR and PR[->]NR). Analysis of dynamics of pellet intake per day revealed that mice that were initially protein-restricted first showed a decrease in pellet intake before increasing on later days and exhibiting a persistent high level of intake once non-restricted diet was available. The group that was initially non-restricted exhibited a blunted response to the same diet manipulation. In addition, we clustered pellet retrieval data into discrete clusters of feeding events and used a mathematical approach to determine the boundary of meals (2-5 pellets), separated from "snacks" (1 pellet) and "feasts" (>5 pellets). We identified alterations in meal patterning in response to diet manipulation with protein restriction increasing "snacking" and leading to increased meal number, and reduced meal size. Moreover, restored access to NR diet, elicited "feasting". These effects depended on the sequence of diets the mice experienced, such that the effects were stronger in initially protein restricted mice compared to those initially non-restricted. In summary, our findings show that manipulation of dietary protein levels affects meal patterning in adult mice.