In 1838 Jens Jakob Berzelius first described protein as protein. From the Greek word proteuo, “I take first place”, from photos, “first place”. The word “most important”, derived from photos, is intended to underline the importance of proteins for life.
Proteins (colloquially called proteins) belong to the basic building blocks of all cells. In humans, they consist of 21 different amino acids to so-called macromolecules.
These can have a length of up to several thousand amino acids, whereby chains with a length of less than approx. 100 amino acids are called peptides and are only referred to as polypeptides and then as proteins from a larger chain length. Besides carbohydrates and fat, protein is one of our most important foods.
Very protein foods are:
- Milk products (cheese and curd)
- Dried pulses (soy: 41.6 %)
Studies of the American biochemist Thomas Osborne and Lafayette Mendel, Professor of Physiological Chemistry at Yale, from 1914 showed that rats receiving animal protein gained weight faster than rats receiving only vegetable protein. This led to the premature conclusion that animal protein was “higher quality” than vegetable protein.
In fact, however, an equivalent diet can be achieved with a few high-quality plant proteins (potato, soya). In the case of protein as food, it depends solely on the proportion of its building blocks, the amino acids.
Protein – Importance for our organism
Proteins have the following very different functions in our organism:
- They determine the structure of the cell and thus ultimately the nature of our body tissue and our entire body structure.
- They transport substances, pump ions, catalyze chemical reactions and recognize signalling substances.
- As keratin they form our hair and nails.
- As collagens, they form up to 1/3 of the total body protein as skin, connective tissue and bone, among other things.
- In the muscles, myosins and actins change their shape, causing muscle contraction and thus movement.
- As enzymes, proteins enable and control very specific (bio)chemical reactions in living organisms.
- They are responsible for the transport of substances important to the body, such as haemoglobin, which is responsible for the transport of oxygen in the blood.
- As antibodies they serve the defense against infection.
- As blood coagulation factors, the proteins prevent on the one hand too much blood loss when a blood vessel is injured and on the other hand too much coagulation reaction with blockage of the vessel.
- In case of famine, the proteins serve the body as a reserve substance for energy production.
Protein in our diet
People cook (denature) their food to make it easier to digest. Cooking changes the physical and physiological properties of proteins, such as in fried eggs, which are denatured by the heat in the pan.
High fever can therefore be life-threatening for humans. Because the body temperature is too high, the body’s own proteins are denatured in fever and can therefore no longer fulfil their vital functions in the organism.
Some proteins of the red blood cells, for example, already denature at 42°C. However, fever actually has a protective function, not a destructive one. The high temperature of fever is supposed to destroy and render harmless intruders and foreign bodies, so-called antigens. These antigens usually denature at lower temperatures than the body’s own proteins.
protein has a large number of functions in our body. It is necessary to build up and maintain the body cells and helps to heal wounds and diseases. The minimum requirement for proteins per day is 0.5 grams/kg body weight.
For normal performance, an adult should consume about 0.9 to 1.1 grams of protein per kilogram of body weight with food every day, while pregnant and breastfeeding women need more.
However, the need for protein does not increase during physical activity. The above-mentioned reference values for protein intake are based on the nutrition report of the DGE (= German Nutrition Society) of 25.03.2009.
A protein deficiency can cause the following symptoms:
- hair loss (97-100 % of hair consists of proteins – keratin)
- In the worst case, the disease Kwashiorkor is caused by protein deficiency. People (mostly children) who suffer from Kwashiorkor can be recognized by their so-called hunger belly, which is caused by an excessive storage of water (edema).
- Other symptoms are muscle weakness, growth disorders and fatty liver.
- Prolonged protein deficiency leads to marasmus (severe disease with massive underweight, partial organ loss, etc.) and death.
However, protein deficiency is extremely rare in industrialised countries and only occurs in extremely low-protein diets.
Protein in sports
In the relevant Internet forums, the demand for protein is being pushed up in an almost inflationary manner. Here the phenomenon is confirmed, which – if they are repeated only often enough – also untruths become the “truth” sometime. Partially fabulous 4 to 5 gram protein per day, per kg body weight are recommended! An athlete with 75 kg body weight would then have to consume approx. 1.2 kg meat per day. Converted that is approx. 1500 kcal only at proteins.
Nevertheless, there are still simple minds (or bona fide people) who believe in such recommendations. You can find a detailed article about protein in sport at Protein – the key to success?
The average German mixed diet contains about 100 grams of protein per day, more than enough protein. Although protein powder is often advertised as essential for amateur athletes, covers “Our usual diet also covers the protein needs of athletes”, according to a report by the Ministry of Food and Rural Areas of Baden-Württemberg.
Reference values for daily protein requirements
|g/kg body weight/day||g/daya|
|0 to less than 1 month||2,7||14||14|
|1 to less than 2 months||2,0||11||11|
|2 to less than 4 months||1,5||8||8|
|4 to under 6 months||1,3||11||11|
|6 to less than 12 months||1,1||9||9|
|1 up to under 4 years||1,0||14||13|
|4 to under 7 years||0,9||18||18|
|7 to under 10 years||0,9||26||26|
|10 to under 13 years||0,9||37||38|
|13 to under 15 years||0,9||50||49|
|Youth and adults|
|15 to under 19 years||0.9||0.8||62||48|
|19 to under 25 years||0,8||57||48|
|25 to under 51 years||0,8||57||48|
|51 to under 65 years||0,8||55||47|
|65 years and older||0,8||53||46|
|Pregnancy from 4th month||58|
|aThese values have been updated based on the new DGE reference weights.
bca. 2 g protein supplement per 100 g secreted milk
What happens to excess protein?
- One too much protein is broken down by the body. Energy, glucose and uric acid are the main waste products. The glucose obtained from the protein is used directly for energy production if required.
- If the supply of glucose to the tissues is greater than their consumption, the excess is first stored in the liver and skeletal muscles. This means that about 200 grams of glucose can be stored in the liver and about 300 grams in the skeletal muscles.
- When these glucose stores are full, the remaining glucose is converted into fat and stored in the body as fat.
- The resulting uric acid is excreted via the kidneys. The higher the protein intake, the higher the uric acid level in the blood. In a large epidemiological study conducted by the Journal of the American Society Nephrology, elevated uric acid levels in the normal population were a risk factor for developing chronic kidney disease.
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