Vegetarian or a Vegan
A person who eats a mixed diet of plants and meats is a omnivore.
What is eaten is food.
A slimming diet
That's a carnivore.
A person that eats all the time is called greedy. If you know a person that eats all the time, it's likely they will get fat. If they don't get fat and they eat all the time, then that is just the way they were born. edit- greed is where you want and keep everything for yourself where as if you eat a lot you would be called a glutton
Any person or creature that eats both meat and vegetables is considered an omnivore. A person who only eats meat is called a carnivore and a person who eats only eats vegetables is called a herbivore.
I would say food chain.
An animal who eats both plants and animals is an omnivore. An animal who eats just plants is a herbivore, and a person who eats just meat is a carnivore.