Meat is rich in protein. Milk soup, especially with clams, is a good source of protein. Legume dishes such as baked beans and pea soup are rich in protein, even if they have little or no meat. Even lemon and vinegar pies are made with protein-rich eggs.
Someone with strong opinions, but who has never studied any biochemistry, told me that plant protein is much healthier than animal protein. This is nonsense. To live we need protein, or more specifically the amino acids it is made from. Proteins are chains of amino acids and we need several types of amino acids.
Meat, milk and eggs are rich sources of amino acids and are high in the important ones. Plants also have proteins made with the same amino acids, but usually are not as much nor containing the same rich amino acid balance.
People, who do not eat meat, need to eat a greater variety of plants to get all of their amino acids. There are other real reasons to avoid eating too much meat, such as too much fat. However animal and plant proteins (amino acids) are not different chemicals. A particular amino acid has the same chemical properties, and the same structure, whether it came from a plant, animal or even a laboratory.
Biochemistry, by Stryer, Berg and Tymoczko
Nutrition : Concepts and Controversies, by Hamilton, Whitney and Sizer