Climate change is altering habitat, particularly in the Arctic, where current trends of sea ice loss are accelerating. The apex predators of the ice, polar bears (Ursus maritimus ), have exhibited declines in body condition and abundance in some regions, thought to be consequences of increased nutritional stress during summer, when ice loss is greatest. Bears hunt on the ice surface, most successfully during April-July when seals use it for parturition and molting. During August-October, hunting is poor and in ~2/3 of the polar bear range, ice retreats from preferred seal habitat over the continental shelf. Some bears spend this period on shore, where foraging is also usually poor. It has been hypothesized that to cope with reduced feeding during summer, polar bears enter "walking hibernation", similar to winter hibernation. However, this theory has not been confirmed. Thus, I sampled bears in the Beaufort Sea during summer and compared their data to expectations for feeding, fasting (but not hibernating), and hibernating. Polar bears reduced activity during late summer on shore and sea ice, contributing to a gradual decline in body temperature. However, these attributes remained well above winter hibernation values. Summer fasting by polar bears on sea ice included low ratios of serum urea to creatinine as in winter hibernation, but otherwise appeared similar to typical fasting. I also sampled bears with unusual access to an alternative food source in summer on shore (whale carcasses, scavenged after human harvest) and found they mostly avoided fasting and maintained body condition, but still exhibited nutritional stress in a year with less sea ice. These bears also demonstrated little skeletal muscle atrophy, likely because of scavenging on whale carcasses and increases in activity during October. Bears on sea ice exhibited moderate atrophy, suggesting that polar bears in summer cannot mitigate atrophy as other bear species do during winter. In conclusion, summer fasting by polar bears in the Beaufort region is largely consistent with typical mammalian fasting, rather than the adaptive fasting suggested by the phrase "walking hibernation".