Fasting-induced increases in food hoarding are dependent on the foraging-effort level.

Two strategies that have evolved to help animals meet energy demands are increases in body fat and in hoarded food. Reliance on each varies, but both are characterized by energy stored in excess of current demands for future use. Fasted Siberian hamsters decrease their lipid stores and, upon refeeding, food hoarding rather than food intake increases. Here, we tested the effect of foraging-effort level on fasting-induced increases in food hoarding and whether decreases in total body fat or individual fat pad masses were associated with the hoarding increases. This was accomplished by housing female Siberian hamsters in a foraging/hoarding system where they earned food pellets upon completion of a programmed number of wheel revolutions (10, 75 or 200 per 75-mg pellet), or had no foraging requirement (free food and an active or blocked running wheel). After baseline, half the hamsters in each group were food deprived for 32 h and then refed (control hamsters were killed after the fast without refeeding). Fasted-refed hamsters increased foraging and food hoarding, especially at the lowest foraging effort, but not food intake, with few exceptions. These responses became progressively smaller as foraging effort increased. Fasting induced similar losses in carcass lipid across foraging efforts, but the lipid loss was not uniform across the fat pads and was not clearly related to hoard size. Collectively, the fasting-induced, increased food hoarding may be triggered by an overall change in energy metabolism rather than by a general or fat-pad-specific decrease in lipid stores.