page_title: Protein (nutrient)
section_title: Sources
hierarchical_section_title: Protein (nutrient) / Sources
caption_attribution_description: English: A chocolate-flavored multi-protein nutritional supplement milkshake (right), consisting of circa 25g protein powder (center) and 300ml milk (left).
context_page_description: Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram; in contrast, lipids provide 9 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.
  Proteins are polymer chains made of amino acids linked together by peptide bonds. During human digestion, proteins are broken down in the stomach to smaller polypeptide chains via hydrochloric acid and protease actions. This is crucial for the absorption of the essential amino acids that cannot be biosynthesized by the body.
  There are nine essential amino acids which humans must obtain from their diet in order to prevent protein–energy malnutrition and resulting death. They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. There has been debate as to whether there are 8 or 9 essential amino acids. The consensus seems to lean towards 9 since histidine is not synthesized in adults.
context_section_description: Protein occurs in a wide range of food. On a worldwide basis, plant protein foods contribute over 60% of the per capita supply of protein. In North America, animal-derived foods contribute about 70% of protein sources. Insects are a source of protein in many parts of the world. In parts of Africa, up to 50% of dietary protein derives from insects. It is estimated that more than 2 billion people eat insects daily.
  Meat, dairy, eggs, soy, fish, whole grains, and cereals are sources of protein. Examples of food staples and cereal sources of protein, each with a concentration greater than 7%, are (in no particular order) buckwheat, oats, rye, millet, maize (corn), rice, wheat, sorghum, amaranth, and quinoa. Some research highlights game meat as a protein source.
  Vegetarian sources of proteins include legumes, nuts, seeds and fruits. Vegetarian foods with protein concentrations greater than 7% 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.
  People eating a balanced diet do not need protein supplements.
  The table below presents food groups as protein sources.
  Colour key:
   Protein source with highest density of respective amino acid.
   Protein source with lowest density of respective amino acid.
  Protein powders – such as casein, whey, egg, rice, soy and cricket flour– are processed and manufactured sources of protein.
caption: Protein milkshakes, made from protein powder (center) and milk (left), are a common bodybuilding supplement
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