Protein

Protein is one of the main building blocks of every living thing. It is one of three main types of food your body needs in large amounts, along with carbohydrates and fats. Your muscles, skin, hair, nails, and most parts of your cells are made mostly of protein. You also need protein in your food to keep your body running.

Proteins are made of smaller pieces called amino acids. There are 20 different amino acids in the human body. Think of them as letters in an alphabet. Just like letters can spell millions of different words, amino acids can be linked in different orders to make millions of different proteins. Each protein has its own job.

Some proteins build body parts. Keratin, the protein in your hair and nails, is one example. Other proteins do work inside cells. Hemoglobin, found in your red blood cells, carries oxygen from your lungs to the rest of your body. Antibodies are proteins your immune system makes to fight germs. Enzymes are proteins that help break down food and run chemical reactions in your cells.

Your body can make most amino acids on its own. But there are nine it cannot make. These are called essential amino acids, and you have to get them from food. That is why eating protein matters.

Protein-rich foods include meat, fish, eggs, milk, cheese, and yogurt. Plants have protein too. Beans, lentils, nuts, seeds, tofu, and whole grains are all good sources. Animal foods usually have all nine essential amino acids in one package. Most plant foods are missing one or two, so people who eat only plants mix different foods, like rice and beans, to get all nine.

Kids need a fair amount of protein because their bodies are still growing. A 10-year-old needs about 35 grams a day. That is roughly the protein in one egg, one glass of milk, and a small piece of chicken combined. Adults who lift heavy things or play sports often need more.

When you eat protein, your stomach and intestines break it apart into amino acids. Your body then takes those pieces and builds them back into the exact proteins it needs. Right now, as you read this, your cells are taking apart proteins from your last meal and using the pieces to build new parts of you.