What are proteins

Man needs a wide range of nutrients to stay healthy and perform various functions. One such important nutrient is protein which is present in the food we eat daily. Proteins are defined as “the basic chemicals that make up the structure of the cells and are essential for growth and repair of tissues”. Proteins are present in every cell and are essential to plant and animal life. They make up about 15% of the mass of an average person.

What do proteins do?

 Proteins are an important constituent of tissues and cells of the body.  They are an important component of muscle.  They are the basic building blocks of the body.  They control vital biochemical reactions in the body.  Proteins supply body building material and hence are important for growth and tissue repair.  Proteins are essential to body’s structure and proper functioning.  Proteins as enzymes promote chemical reactions in the body.  Proteins as antibodies help the body to defend against infection.

Thus, proteins are vital to the living process and carry out a range of bodily functions.

What are proteins made up of?

Proteins are large, complex molecules made up of smaller units called “amino acids”. Though there are thousands of different proteins required by the body, only 20 amino acids are assembled into these varied proteins. These different types of amino acids can be combined in various ways to form long chains called polypeptides. A few polypeptides are straight, but most are bent into complex three dimensional shapes. The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.

Amino acids are of two kinds:

 Essential amino acids which cannot be produced by the body.  Non essential amino acids that can be manufactured by the body itself.

Proteins in the diet

The best sources of proteins are:

 Cheese  Fish  Eggs  Milk  Meat

The proteins in these foods are called “complete proteins” as they contain adequate amounts of all the essential amino acids. However, proteins can be obtained from a variety of other sources, for example,

 Grains  Cereal grains  Legumes  Nuts  Seeds  Pulses  Vegetables These proteins from plant sources are called “incomplete proteins” because they do not contain all the amino acids needed by the body. However, a combination of incomplete proteins can provide all the amino acids when used judiciously. For example, a cereal grain can be combined with a legume to complement the amino acids lacking in each. However, the two foods must be eaten together to provide the correct balance of amino acids.

Protein requirement

The adult requirement of egg protein is 0.7grams per kilogram body weight, while requirement in terms of mixed vegetable protein is 1.0 gram per kilogram body weight. Children require more protein per unit body weight than adults, because new tissues are being laid down during growth. Likewise, pregnant women and nursing mothers also have increased protein requirements.

Insufficient protein in the diet may cause lack of energy, stunted growth and lowered resistance to infections giving rise to a condition called Kwashiorkor. If the diet is very low in calories, the body starts using protein as an energy source and the protein in the muscles is converted into calories. Important muscle mass is lost in this way and leads to weakness.

On the other hand, too much protein can also cause problems in people already having liver and kidney problems. Also, if the main source of protein in the diet is from red meats and dairy products high in saturated fats, it can lead to increase in blood cholesterol levels.

Thus, to sum up, the diet should include a variety of foods to ensure the supply of all amino acids, a healthy balance between calories and proteins should be maintained and healthier choices of protein foods should be made. For example, skim or low fat dairy products should be substituted in place of high fat versions and leaner cuts of meat in place of those containing high saturated fats.

Useful websites

www.bupa.co.uk/health_information/html/healthy_living/lifestyle/diet/nutrition4.html

www.kidshealth.org/kid/nutrition/food/protein.html