While polar bears are almost purely carnivores, adult polar bears only eat the skin and blubber from animals they kill.
Picture from Bear Life
Majority of a polar bears diet comes from hunting seals, which they swipe out of the water and onto the ice. The skin and blubber of seals and other animals like walruses, beluga whales and carrion is rich in calories and fat, providing sufficient nutrition for the older animals. However younger polar bears need the protein to grow, so they do eat meat.