PROTEINS - What they are and what they do

Proteins are one of the three macronutrients – the other two being carbohydrates and fats – that provide the body with building blocks and energy for all bodily functions. Proteins are made up of a series of building blocks known as amino acids. Some of these amino acids are called ‘essential’ amino acids, as they cannot be formed in the body and therefore must come from the food we eat. This is one of the reasons why it is important to eat protein every day.

Compared to carbohydrates and fats, proteins have the greatest variety of roles in the body, with the main one being the building and repairing of tissues. Other functions of protein include being a major component of enzymes and being used in the production of hormones, brain chemicals and antibodies (which play a role in immunity). Unlike carbohydrates, providing energy is not a significant role for proteins.

There are two main types of protein:  complete and incomplete. Complete proteins contain all of the essential amino acids in quantities sufficient enough to meet the body’s requirements.  Most proteins from animal sources (e.g. dairy, eggs, meat, poultry and fish) are complete proteins. Incomplete proteins are deficient in at least one of the essential amino acids. 

Plant proteins tend to be limited in one or more essential amino acids. For example, beans are low in the amino acid lysine, while rice is high; therefore by combining rice and beans in a meal it ensures that the body is getting sufficient levels of this essential amino acid. These types of food pairings are called "complementary proteins". Examples include grains and legumes or legumes and seeds and nuts. People following a vegetarian diet must eat protein foods that have complementary proteins so that the essential amino acids missing from one protein food can be supplied by another.

The quality of a protein can also be measured by how well the body can absorb and utilize it. This measurement is referred to as the ‘Biological Value’ (BV) of a protein. The higher a protein’s BV is, the more it promotes tissue repair and growth – including lean muscle.  Animal sources of protein have higher BVs compared to vegetable sources of protein. The natural, whole food source with the highest BV is eggs, against which all other protein containing foods are rated in comparison.

In general, 10% to 12% of dietary calories should come from protein.  Adults typically need 1 gram (0.035 oz) of protein per 1 kilogram (2.2 lbs) of body weight.  Infants need 3 times this amount, while children and adolescents need approximately 2.5 times this amount. Note that 1 gram of protein equals 4 calories.

Food sources of protein include meat, poultry, fish, dairy, eggs, legumes, nuts and seeds. When buying animal sources of protein, choose those from organically raised and pasture-fed animals.

Strive to include some healthy sources of protein in your meals and snacks every day.


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