The food eaten by mammals varies based on the type of mammal, the season and the environment. Mammals can be classified as carnivores, herbivores and omnivores. Carnivores primarily eat meat, herbivores primarily eat plants and omnivores eat both.
Carnivores are designed to eat animal tissue. They are either hunters that kill and consume other animals or scavengers that find and consume carcasses. Although carnivores can eat plants, they cannot digest it easily. They have jaws that open wide and limited facial muscles. They swallow chunks of food without chewing, and their stomach breaks down the food.
Herbivores are designed to eat and digest plants. They have complex facial muscles, with jaws that can't open wide. Herbivores that eat a high amount of indigestible fiber, which are called ruminants, have complex stomachs to extract nutrients from their food. Herbivores that eat mostly digestible fiber, which are called non-ruminants, have simple stomachs with one chamber.
Omnivores combine the design of a carnivore or herbivore with a physical adaptation that allows them to consume other types of food. Bears and raccoons have the anatomies of carnivores, but they can survive on a plant-based diet. Humans have the anatomy of a herbivore but evolved the ability to eat meat.