<P> Protein can be found in a wide range of food . The best combination of protein sources depends on the region of the world, access, cost, amino acid types and nutrition balance, as well as acquired tastes . Some foods are high in certain amino acids, but their digestibility and the anti-nutritional factors present in these foods make them of limited value in human nutrition . Therefore, one must consider digestibility and secondary nutrition profile such as calories, cholesterol, vitamins and essential mineral density of the protein source . On a worldwide basis, plant protein foods contribute over 60 percent of the per capita supply of protein, on average . In North America, animal - derived foods contribute about 70 percent of protein sources . </P> <P> Meat, products from milk, eggs, soy, and fish are sources of complete protein . </P> <P> Whole grains and cereals are another source of proteins . However, these tend to be limiting in the amino acid lysine or threonine, which are available in other vegetarian sources and meats . Examples of food staples and cereal sources of protein, each with a concentration greater than 7 percent, are (in no particular order) buckwheat, oats, rye, millet, maize (corn), rice, wheat, sorghum, amaranth, and quinoa . </P> <P> Vegetarian sources of proteins include legumes, nuts, seeds and fruits . Legumes, some of which are called pulses in certain parts of the world, have higher concentrations of amino acids and are more complete sources of protein than whole grains and cereals . Examples of vegetarian foods with protein concentrations greater than 7 percent include soybeans, lentils, kidney beans, white beans, mung beans, chickpeas, cowpeas, lima beans, pigeon peas, lupines, wing beans, almonds, Brazil nuts, cashews, pecans, walnuts, cotton seeds, pumpkin seeds, hemp seeds, sesame seeds, and sunflower seeds . </P>

Importance of nitrogen in the formation of protein