You probably know you need to eat protein, but what is it? Many
foods contain protein (say: pro-teen), but the best sources are
beef, poultry, fish, eggs, dairy products, nuts, seeds, and
legumes like black beans and lentils. Protein builds, maintains,
and replaces the tissues in your body. (Not the tissues you blow
your nose in! We mean the stuff your body's made up of.) Your
muscles, your organs, and your immune system are made up mostly
of protein. Your body uses the protein you eat to make lots of
specialized protein molecules that have specific jobs. For
instance, your body uses protein to make hemoglobin (say: hee-
muh-glow-bin), the part of red blood cells that carries oxygen
to every part of your body. Other proteins are used to build
cardiac muscle. What's that? Your heart! In fact, whether you're
running or just hanging out, protein is doing important work
like moving your legs, moving your lungs, and protecting you
from disease. All About Amino Acids When you eat foods that
contain protein, the dige