Any physically active individual will know the importance of protein in their diet.
As a key structural element of muscle tissue, protein is essential to help develop bigger, stronger muscles and aid recovery and repair after exercise.
However, thanks to our modern lifestyles that focus on convenience more so than anything else, our diets are often deficient in a number of important macro- and micronutrients, including protein. While we may get our daily recommended dose of protein, many of us seldom give the concept of protein variety a second thought. As such our main sources of protein are animal-derived, in the form of dairy, meat and eggs.
However, protein is essential for more than just muscle development. Proteins play a vital role in many biological processes, including enzyme production and function, metabolism regulation, immune response, as well as cell development and function.
Each protein within the body has a specific function and varies in structure. They are constructed from a set of 21 amino acids, eight of which are essential as they cannot be produced by the human body and therefore need to be supplied through the diet. There are several types of proteins, which all have distinct functions.
The two main classes of proteins include:
Fibrous proteins – These fibre-like proteins play a protective and structural role in the functioning of the body as they are constituents of connective tissue, muscle fibre and tendons. An example is the cell wall of myosin in skeletal muscle.
Globular proteins – The polypeptide (amino acid) chains in globular proteins are folded together into a knot-like shape. Globular proteins usually change faster than fibrous proteins and play a variety of roles.
Minimum recommended daily protein intake guidelines:
- Endurance athlete: 1.2-1.6 grams per kilogram of lean bodyweight per day
- Strength and power athlete: 1.6-1.8 grams per kilogram of lean bodyweight per day
- Bodybuilders and physique conscious individuals: 1.8-2.0 grams per kilogram of lean bodyweight per day
The structure of a protein will determine what role it has to play in your body:
- Enzymes – Biological catalysts that are responsible for initiating and controlling (speeding up) important biochemical reactions in the body. An example is pepsin, which works in the stomach to break down proteins in food.
- Hormones – Chemical messengers responsible for initialising a response in the body. Some hormones have a regulatory effect. Examples include insulin and somatotropin.
- Antibodies – Specialised proteins involved in defending the body against antigens (foreign invaders) such as bacteria, fungi and viruses.
- Transport/conjugated proteins – Carrier proteins that move molecules from one place to another around the body. Examples include haemoglobin and cytochromes.
- Storage proteins – Store amino acids.
- Contractile proteins – Responsible for movement through muscle contraction. Examples include actin and myosin.
- Membrane proteins – Globular proteins that play a role in transporting ions in and out of the cell.
Proteins are synthesized in the body through a process called translation. Translation occurs in the cytoplasm – the fluid that fills a cell – and involves the translation of genetic codes, assembled during DNA transcription, into proteins. Cell structures called ribosomes help translate these genetic codes into the amino acid (polypeptide) chains, which undergo several modifications before becoming fully functioning proteins.
To ensure we have all the amino acids required to effectively fulfill these functions it is essential that we consume a broad spectrum of protein sources. The reason for this is that, while some protein sources contain excellent amino acid profiles, they all have different amino acid profiles and combinations. The quality of protein we consume also varies in the foods we eat. For these reasons it is essential that you mix your protein sources throughout the day, especially if you mainly derive your protein from plant sources.
Animal protein sources such as beef, poultry, fish, venison, lamb, pork and eggs are considered complete proteins as they contain all eight essential amino acids. Plant-based protein sources are generally incomplete proteins as they contain some, but not all, the essential amino acids. For this reason, it is vitally important that vegans and vegetarians consume a variety of protein sources to meet their body’s needs. Incomplete protein source can be consumed together to deliver a complete amino acid profile with each meal or throughout the day. Incomplete proteins that are consumed in combination to create a complete protein source are referred to as complementary proteins.
However, there are a few plant-derived protein sources that have a complete amino acid profile. Soybeans, for instance, are a nutritionally complete protein and are a cheaper source of protein than meat and dairy. It is also low in fat and is cholesterol-free. Soy also contains important substances like saponins, phytosterols and isoflavones. Saponins support healthy immune function and help to reduce cholesterol absorption in the body. Phytosterols also help to maintain cholesterol levels, while isoflavones are powerful antioxidants.