Proteins – types and functions

Protein is essential for growth and repair of the body – tissue, hair and nails. It forms the structural and functional elements of body cells.

So, what is protein?
Protein is a macronutrient made up of amino acids. Protein contains carbon (C), hydrogen (H) and oxygen (O) like carbs do, but unlike carbs and fat, protein also contain nitrogen (N).


As soon as you become vegetarian you’ll get the question “Do you eat enough protein?”. Well, it’s not only which protein you eat that is important, but also the quality of the protein. Adults need around 0.75 g of protein per kg of body weight. So if you weigh 60 kg you need to eat around 45 g of protein.

Amino acids

There are 20 amino acids. Our body use them to synthesize proteins. There are 3 classes of amino acids; essential, non-essential and conditionally essential.
The 9 essential amino acids cannot be made in the body, so it’s essential that they are part of the diet.
Non-essential, or dispensable amino acids can be made in our body, so we don’t need to include them in the diet. Conditionally essential amino acids are essential for some people in certain situations when people have certain diseases, such as PKU. People with PKU can’t synthesize tyrosine, so it’s essential to them.

Essential amino acids – can’t be made by the body

  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

Conditionally essential amino acids – some people need to include them in the diet

  • Arginine
  • Cysteine
  • Glutamine
  • Glycine
  • Proline
  • Tyrosine

Non essential amino acids – can be made in our body

  • Alanine
  • Asparagine
  • Aspartic acid or Aspartate
  • Glutamic acid or Glutamate
  • Serine

The function of protein
Protein helps us with a number of things such as:

Structural: Protein such as collagen are important for the structure of tissues.

Enzymes: The majority of enzymes are proteins. Enzymes starts and speed up (catalyze) a chemical reaction. Enzymes names usually ends in -ase such as “amylase”.

Hormones: Many hormones are proteins. A hormone is a compound produced in one tissue, released into circulation and then has an effect on an organ. Most hormones are produced from several organs, known as endocrine organs. Insulin is an example of a hormone that is a protein.

Fluid balance: Proteins help maintain the balance between fluids in the plasma (which is a fluid part of the blood) and the interstitial fluid (which is a fluid surrounding cells).

Acid-base balance: Proteins serve as buffers preventing the pH of the body getting too high or too low.

Transport: Transport proteins move molecules though circulation or across cell membranes. Hemoglobin transports oxygen through the body.

Immune function: Antibodies are proteins that recognize antigens and bind to inactivate them.

The quality of protein
Protein can be either “complete” or “incomplete”. Complete protein provides all the nine essential amino acids. Animal protein such as meat, fish, dairy and egg are usually complete. Incompleate protein is too low or is lacking essential amino acids. Most plant foods (soy is an exception) are incomplete proteins, which is not good news for vegans.

For example:
Beans and legumes – limited in methionine and tryptophan
Nuts and seeds – limited in methionine and lysine
Grains – limited in lysine
Vegetables – limited in methionine and lysine.

The good news is that this can be solve by combining different protein sources, such as milk and cereal, beans and rice, kidney bean chili served with tortillas, bread with cheese, lentil soup with bread, hummus and pita bread and so on.

How well does the body digest a protein?

Denaturation of protein is the breakdown of protein. The breakdown is important for the uptake of vitamins contained in the food. When a macronutrient – like protein – binds a micronutrient – like a vitamin – the digestibility is important for the uptake of the vitamin. If we can’t digest the protein, we can’t free the vitamin and the body can’t absorb the vitamin. For example, a steak contains more vitamin B12 than chicken, but chicken is more easily digested, thus easier for the body to take up B12 from chicken than from steak.

Lack of protein
In the western world lack of protein is rare, but it is a 3rd world disease. PEM or Protein Energy Malnutrition can cause Kwashiorkor with symptoms like swollen belly and edema. It can affect children who are weaned away because of the birth of a second child.
Marasmus is another disease, which is basically a total lack of nutrition in the diet, often caused by starvation.

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