Why? Protein is a key macro-nutrient for developing and maintaining a healthy body. It provides the body with: energy in the form of calories, building materials for muscles, and essential amino acids needed for the body's processes. The basis of the body is protein, right down to DNA, the building blocks of life itself!
Sounds great? Why not have a diet that contains A LOT of it, right? Diets have come out involving huge amounts of protein and virtually no carbohydrates. The theory is to build lean muscle making the body look good. But there are consequences. The body cannot process large amounts of protein so the left overs have to go somewhere. That place is the kidneys. Too much protein can damage them. This is why certain chronic disease states like early onset kidney failure require reduction in protein intake.
How much? Like other macro-nutrients, there is not one size fits all daily requirement for protein. Certain individuals will require more, some less.
Seafood
Red Meats
Legumes
Poultry