Protein, called Eiweiß in German, is one of the three macronutrients in the diet, alongside carbohydrates and fat. It consists of amino acids that link into long chains and, depending on how they fold, form very different structures. In the body, protein performs numerous tasks: it is a building material for muscle, skin and connective tissue, it forms the basis for enzymes and hormones, and it is involved in transporting many substances.
In practice, protein occurs in both animal and plant foods. Meat, fish, eggs and dairy products traditionally supply a lot of protein, as do pulses, tofu, nuts and some cereals. For healthy adults, the German Nutrition Society (DGE) gives about 0.8 g of protein per kilogram of body weight per day as a reference value, and from about age 65 a figure of about 1.0 g is often cited. People who do strength training or are on a diet often follow a range of 1.2 to 2.0 g per kilogram in sports science.
People with kidney disease should generally discuss their protein intake with a doctor. For an overview of different protein sources, see the page Protein types, and for how to estimate your individual requirement, see the page Protein requirement.