Proteins, Classification and Functions of Proteins

Proteins are organic compounds that contain carbon, hydrogen, oxygen, and nitrogen atoms; some proteins also contain sulfur.

Energy from Proteins

•      1 gram of protein supplies 4 kcal (the same as CHO).

•      Proteins should supply 10-15% of your total daily kcals.

Classification of Proteins

Complete proteins (High-biological-value proteins) contain all of the essential amino acids. Complete proteins are primarily animal proteins, such as those in meats, poultry, fish, dairy products, and eggs.

Incomplete proteins (Low-biological-value proteins) lack one or more of the essential amino acids, usually lysine, methionine, and tryptophan. Most vegetables are incomplete proteins. 

Essential amino acids

•      The body cannot make essential amino acids. As a result, they must come from food.

•      The nine essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

Nonessential amino acids

•      "Nonessential" means that our bodies produce an amino acid, even if we don't get it from the food we eat.

•      They include: alanine, asparagine, aspartic acid, and glutamic acid.

Functions of Proteins

Growth and replacement: clotting factor production, collagen synthesis, epithelial  cell proliferation, fibroblast proliferation.

Immunity: antibodies, white blood cell production and migration, cell-mediated phagocytosis.

Fluid balance: intracellular osmotic pressure, albumin, maintenance of blood volume

Sodium and potassium balance.

Energy source