According to the National Wildlife Federation, all bears are classified as omnivores, not herbivores. Some species consume more meat, like polar bears, while others consume more vegetation, like giant pandas, but they all share similar digestive systems. This allows them to adapt effectively to many different environments around the world.
In North America, the black, brown and grizzly bear all have similar diets. Their primary source of food is normally the most abundant, which leads many of them to subsist on roots, berries and other vegetation. However, when fish are abundant, they become the primary food source of these bears instead. Even so, it's not unusual for a bear to take down a deer or elk if the opportunity presents itself.