Protein (nutrient)

Protein is a special part of your body.

It is in every cell you have. It helps make your skin, hair, and bones.

Protein also gives you energy to move. You can find it in many foods. You might eat meat, fish, or eggs. You can also eat beans, nuts, and seeds. Some people even eat insects for protein. Eating these foods helps your body stay strong.

Protein is a vital part of your body.

It is found in every single cell. Protein makes up your skin, hair, and bones. It is also found in your blood and muscles.

Proteins are made of tiny building blocks. We call these building blocks amino acids.

Some amino acids are essential. This means your body cannot make them. You must get them from the food you eat. There are nine essential amino acids for humans.

Your body uses a set of steps to use protein. This is called digestion. First, your stomach uses acid to break protein down. Then, your small intestine breaks it into even smaller parts. Finally, your body absorbs the amino acids.

You can find protein in many foods. Meat, fish, and eggs are good sources. You can also eat beans, nuts, and seeds.

Many people around the world eat insects for protein. Some people use protein powders to get more. But a balanced diet is usually enough for most people.

Proteins are vital building blocks for every living thing. After water, proteins make up more mass in an organism than any other molecule. They are found in every single cell in your body. Proteins help build your skin, hair, blood, and bone. They are also very abundant in your muscles. Beyond building tissue, proteins act as fuel for your body. They provide the same amount of energy as carbohydrates.

To understand how protein works, you must look at amino acids. Proteins are long chains made of these small parts. These chains are held together by peptide bonds. When you eat protein, your body must break these chains apart. This process is called digestion. In your stomach, hydrochloric acid and an enzyme called protease begin the work. They break the proteins into smaller polypeptide chains. Eventually, these are broken down into single amino acids in the small intestine.

Not all amino acids are the same. Your body can make five of them on its own. However, there are nine essential amino acids that you cannot make. You must get these from the food you eat to stay healthy. These nine are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. If you do not get enough, it can lead to protein-energy malnutrition. Scientists have even debated if there are eight or nine essential types.

People find protein in many different types of food. In North America, about 70% of protein comes from animal sources. In many parts of Africa, insects provide up to 50% of dietary protein. More than 2 billion people eat insects every day. Plant foods provide over 60% of the world's protein supply. You can find protein in grains, legumes, nuts, and seeds. Some foods like oats, rice, and wheat have more than 7% protein.

Scientists use special tests to see how much protein is in food. One common way is to measure nitrogen. Since nitrogen is a part of amino acids, it helps find the protein. This is often called "crude protein" content. Some places now use "true protein" measurements to be more exact. This helps make sure the nitrogen comes from real protein and not other things. Some industries even use solar power to grow microbial protein in large vats.

Proteins are essential nutrients that serve as fundamental building blocks for life. After water, proteins account for more mass in an organism than any other type of molecule. They are present in every single cell and act as structural components for tissues like skin, hair, blood, and bone. Proteins are especially abundant in muscle tissue. Beyond structure, they serve as a vital fuel source for the body. They provide an energy density of 17 kJ (4 kcal) per gram, which is the same as carbohydrates.

To understand protein, one must look at its molecular structure. Proteins are polymer chains composed of individual units called amino acids. These amino acids are linked together by chemical connections known as peptide bonds. The specific sequence and types of amino acids determine the unique three-dimensional structure of each protein. This shape is critical because it dictates the protein's specific function. Proteins also act as cellular messengers, such as hormones, and as transport molecules like enzymes and antibodies.

Digestion is the process of breaking these complex chains back down into usable parts. This process begins in the stomach, where hydrochloric acid and the enzyme protease work together. They break proteins into smaller polypeptide chains. As the food moves into the small intestine, other enzymes like trypsin and chymotrypsin continue the work. Most proteins are eventually reduced to single amino acids or very small peptides. Before they can be absorbed by the intestinal cells, most peptides longer than four amino acids must be broken down into single amino acids.

Amino acids are categorized based on whether the body can produce them. There are five amino acids that the human body can synthesize on its own: alanine, aspartic acid, asparagine, glutamic acid, and serine. There are also six conditionally essential amino acids. These are arginine, cysteine, glycine, glutamine, proline, and tyrosine. Their synthesis may be limited during specific medical conditions, such as prematurity in infants or severe catabolic distress.

Most importantly, there are nine essential amino acids that humans must obtain through their diet. These include phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. While there has been debate about whether there are eight or nine, the consensus leans toward nine because adults do not synthesize histidine. A lack of these amino acids can lead to protein-energy malnutrition, which can be fatal.

Dietary sources of protein vary greatly across the globe. Plant-based foods contribute over 60% of the per capita protein supply worldwide. In North America, however, animal-derived foods contribute about 70% of protein sources. In some parts of Africa, insects provide up to 50% of dietary protein, and more than 2 billion people eat insects daily.

Many grains and legumes are excellent sources. Staples like buckwheat, oats, rye, millet, maize, rice, wheat, sorghum, amaranth, and quinoa all contain protein concentrations greater than 7%.

Scientists use specific methods to measure the protein content in food. A common technique is measuring nitrogen content, as nitrogen is a fundamental component of amino acids. This is often called "crude protein" content. Using the Kjeldahl method or the Dumas method, scientists multiply the nitrogen level by a factor to estimate total protein. On food labels, this is often calculated by multiplying nitrogen by 6.25. However, this method cannot distinguish between true protein and non-protein nitrogen (NPN). To ensure quality, some industries now use "true protein" measurements, which specifically measure peptide bonds to ensure the nitrogen comes from actual protein.