Proteins provide the building material for the growth, maintenance and repair of all body tissues. They function as enzymes, hormones, antibodies and hemoglobin to carry oxygen. Maintenance of water and acid-base balance in the body are other important functions.

Proteins give shape and strength to living things. Hair and nails are made of protein, and within our cells, protein strands provide shape and structure.

Proteins even help hold us upright! Bones are composed of calcium and phosphorus embedded in a protein lattice work, while a special protein called collagen makes up most of our connective tissues – it keeps our complexions, tendons and ligaments strong and supple.

Proteins are instrumental in the growth, maintenance, and repair of all tissues. When you cut your finger, the proteins fibrin and thrombin help your blood clot to stop the bleeding. If bacteria enter the wound, then antibodies – special proteins formed by the immune system – attack these invaders. Then, to speed healing, new skin cells are formed under the scab.

Perhaps the cut looks quite deep, and you have to head to the emergency room for stitches. While waiting, you grab a candy bar from the vending machine. The refined sugar in the candy bar causes a rapid rise in your blood glucose, triggering a release of insulin from your pancreas.

Insulin, a protein hormone, “unlocks” the doors to the cells and lets in the glucose, where it can be used for energy. How fast your body is able to break down food is decided by yet other protein hormones made in the thyroid gland!

There are many more proteins with specialized functions. Muscle fibres can contract because of unique proteins that respond to electrical impulses. Some proteins control the balance of water, acidity and salt levels in the blood. And most of us are familiar with hemoglobin, a red protein that makes up most of red blood cells and carries oxygen to every cell in the body.

Proteins can be used for energy when carbohydrates or fats are scarce, but produce byproducts that the body must detoxify and eliminate.

Carbohydrates and fats are composed only of carbon, hydrogen and oxygen, and are used to provide energy. Proteins contain nitrogen as well, and can be “burned” for energy when carbohydrates and fats are scarce. One gram of protein provides the same amount of heat energy as one gram of carbohydrates – 4 calories.

When proteins are burned for energy, the nitrogen forms ammonia, a toxic by-product that must be converted to urea by the liver. Urea must then be eliminated from the body by the kidneys.

You can see why the body prefers to use carbohydrates or fats for energy–they are clean-burning fuels!

Proteins are extremely large, complex molecules whose shape is essential to biological function.

Proteins are able to perform so many varied functions because of their unique composition and structure. Just as large starch molecules are made up of many single sugars joined together, proteins are made up of many small organic molecules called amino acids linked together in chains.

Many proteins have thousands of amino acids in their sequence. With even one amino acid out of sequence, the protein cannot properly perform its job.

Essential Amino Acids
Humans use about 20 different amino acids, combined in a vast variety of ways, to construct all the different proteins required by our bodies. The body is able to formulate 12 of the 20 amino acids used to make proteins, but eight of them (10 in infants) cannot be manufactured and must be obtained in food. These are called essential amino acids because they are essential for health.

The basic unit of protein structure is the amino acid. All amino acids contain carbon, hydrogen, oxygen and nitrogen. Human proteins are manufactured using 20 different amino acids, eight of which adults must obtain from our food supply. Both plant and animal foods can supply all the essential amino acids.

Dietary Sources
The body is only able to store excess carbohydrates and fats – not protein. Fortunately, plant and animal foods are able to supply us with a steady source of the essential amino acids that make up protein. This is very important because there is constant protein destruction in the body, so we must continually replenish the supply of essential amino acids.

Foods containing all the essential amino acids are labeled “complete proteins,” while foods providing only some of the essential amino acids are called “incomplete proteins.”

COMPLETE PROTEINS: Eggs, fish, dairy products, meat, and poultry provide complete, good quality protein. However, they are high in saturated fats and cholesterol, and completely lacking in carbohydrates and fibre.

INCOMPLETE PROTEINS: Grains and legumes are incomplete proteins. Generally, grains lack the essential amino acid lysine, and legumes lack methionine.

Complementary Proteins
Alone, grains and legumes are incomplete proteins, but eaten together their amino-acid profiles complement each other to provide complete protein. Grains supply the methionine that legumes lack, and legumes can supply the lysine that’s missing in grains.

Grains such as brown rice, corn, whole wheat, millet, quinoa and legumes such as peas, beans and lentils are excellent sources of protein when eaten together. Depending on the method of preparation, these foods are very low in saturated fats and cholesterol.

There are many benefits to the traditional pairings of beans and rice, tortillas and beans, and pitas with hummus. These complementary proteins provide both carbohydrates and protein, a wide variety of vitamins and minerals, and fibre.