What Are Proteins And What Do They Do

What are proteins?

Proteins, called proteins in the technical language, are organic compounds that, like carbohydrates and fats, contain the elements carbon (C), hydrogen (H) and oxygen (O), but additionally nitrogen (N). Besides, sulphur (S) is also present in some proteins. The proteins determine the function and structure of the human body to a decisive extent. Therefore, they are not only indispensable building material of human cells, but they are also involved in numerous metabolic processes in a variety of ways.

The building blocks of the proteins are amino acids. According to the number of amino acids that make up a protein, oligopeptides are distinguished with less than ten amino acids, polypeptides composed of 10-100 amino acids, and proteins with more than 100 amino acids. The sequence of amino acids used to make the proteins is stored in the DNA. Therefore, in theory, an infinite number of proteins can be formed since the amino acids can be combined and lined up as desired. On the other hand, humans produce “only” 30,000 proteins, which perform a variety of functions in the body.

In the human organism, 20 different amino acids are required for protein synthesis. 9 of these are essential. Essential amino acids cannot, therefore, be produced by the body itself and must, therefore, be supplied with food in sufficient quantities. These 9 also include the three so-called branched-chain amino acids valine, leucine and isoleucine. These branched-chain amino acids are also called BCAA’s. Four other amino acids are conditionally essential, i.e. they cannot be produced in sufficient quantities by the body itself under certain conditions (e.B. in infancy, with high physical stress) and thus become essential in such situations.

Essential amino acids

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

Conditionally essential amino acids

  • Tyrosine
  • Cysteine
  • Glutamine
  • Arginine


Occurrence of proteins

Meat, fish, milk, dairy products, and eggs are sources of animal origin, while cereal and soy products, legumes, and nuts are plant sources. Vegetable protein sources are lower than animal proteins in terms of biological value (see below).

Digestion, absorption and breakdown of proteins

Proteins are digested in the stomach’s acidic environment by enzymes formed by the stomach wall, which serve to split the protein chains into shorter chains. The stomach enzymes are rapidly inactivated in the small intestine, and the enzymes of the pancreas break down the already shortened protein chains into individual amino acids. At the end of digestion, the amino acids are absorbed into the intestinal cells with the help of transporters in the intestinal wall. They enter the blood and finally into the liver. The amino acids can be combined into proteins and released back into the blood to allow other organs such as the muscles.

The body’s own proteins are constantly being set up and broken down. Ammonia is produced when amino acids are broken down in the cells. This is toxic to the body and must, therefore, be removed. Therefore, the resulting ammonia is converted into urea with great energy expenditure and excreted via the kidney with the urine. In contrast to ammonia, urea is relatively non-toxic and very well water-soluble, and that is why the organism affords such a wasteful urea cycle.

If the protein intake increases, more urea is formed, which binds a lot of water to itself because of its good water solubility. Therefore, with a larger amount of urea, you also lose more fluid. If you eat a high protein and do not absorb enough fluid, the kidneys are unnecessarily stressed.


Functions of proteins in the body

Proteins occur in the human organism as a component of:

  • hormones (peptide or proteohormones)
  • Enzymes
  • Membrane proteins of the cell wall (e.B receptors or transport proteins)
  • Support and scaffolding whites (e.B. collagen, keratin or elastin)
  • Contractile proteins (e..B. actin and myosin filaments as contractile elements of the muscle)
  • Plasma egg whites (e.B. albumin)
  • Transport proteins (e.B. hemoglobin, myoglobin and certain plasma proteins)
  • Blood clotting factors
  • Antibodies
  • In the case of energy supply, only the reserve function

In the case of energy supply, protein only has an important meaning in exceptional cases (e.B. with deficient energy intake or under several hours of endurance load).

Proteins have the same energy value as carbohydrates (17 kJ/g (= 4 kcal/g)) and are significantly lower than those of fats (39 kJ/g (=9 kcal/g)).


The daily need for proteins

The need for proteins in athletes in both strength and endurance sports is higher, about 1.2-1.8 g/kg body weight daily. Once the demand is met, an even higher protein intake does not bring any benefits. However, with optimal intake timing, the protein synthesis rate can be maximized, which has a positive effect on the adaptation of training stimuli (e.B. building muscle mass).


Quality of proteins

If we believe most manufacturers of protein supplements’ recommendations, pretty much everything falls into the category of “high-quality protein”. Unfortunately, this is not the case objectively.

Regarding the value of different protein sources, there are several “scores” used in practice. In addition to the outdated (and often undefined) “biological value”, this is especially true for the “Protein Digestibility Corrected Amino Acid Score” (PDCAAS), which, however, should be consistently replaced by the “Digestible indispensable amino acid score” (DIAAS), as recommended by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO).

This is defined as DIAAS (%) = 100 x [(quantity in mg of a digestible indispensable amino acid in 1 g of the food protein) / (quantity in mg of the same digestible indispensable amino acid in 1 g of the reference protein)], wherein the digestibility refers to the digestibility in the small intestine (most accurate assessment of digestibility). Diana thus assesses the ability of a protein to meet the needs of human metabolism.

Simplified about DIAAS, the following can be stated:

  • The quality of a protein source is ultimate “the delivery” of the indispensable amino acids to the body.
  • The protein source’s quality consists of biological availability, amino acid profile (distribution), and the number of essential amino acids.
  • DIAAS can be over 100%. Milk protein (total fraction) has a DIAAS of 122%.
  • High-quality foods achieve higher DIAAS than in the unenriched state thanks to enrichment by high-quality protein sources or at most free amino acids.


So what does this mean in terms of supplements?

Well, it is clear in any case that many protein supplements touted as “high-quality” (e.B. pure plant proteins without the addition of essential amino acids, collagen hydrolysate, etc.) are not optimal in terms of human metabolism. Also, we can state that protein supplements based on milk proteins have high DIAAS and are, therefore, of high quality. However, if we go a step further with the scientific analyses and consider the direct effects of the intake of protein sources on protein synthesis and protein degradation, we can further specify the benefits of supplements.


Missupply of proteins

If the protein supply is insufficient, physical and mental performance initially decreases. Furthermore, fertility and the immune system are impaired, resulting in increased susceptibility to infectious diseases. Acceleration of aging processes in the body can also occur as part of a protein deficiency. In case of massive protein deficiency, there may be pronounced edema, i.e. fluid deposits in the tissue.

A very high protein supply (>2.0 g / kg BW per day) increases the demand for kidneys and liver through increased urea formation. However, this is not a problem for healthy organs.


Protein balance

All tissues of our body consist to a large extent of proteins (protein). This (and thus also our tissues, such as . B muscles, skin, hair, connective tissue, etc.) is constantly subject to degradation and degradation processes. Our body must be constantly supplied with fresh building materials. The building materials necessary for tissue building are called amino acids, which our body obtains during digestion from food proteins. By consuming food proteins, we essentially supply our body with the building blocks necessary for tissue building.

The relationship between the breakdown and breakdown of body proteins is called protein balance. Changes in protein breakdown and breakdown are triggered by both training and diet. These changes result in the protein balance being increased or reduced within the shortest possible time depending on the training and/or nutrition measures. You end up with net protein mass (positive protein balance) or degradation (negative protein balance). For example, strength training without food supply leads to increased protein synthesis (protein build-up). Still, the simultaneously increased protein degradation leads to a negative protein balance (i.e. net to a breakdown of body protein).


How does food protein affect protein balance?

The above example shows that even if a specific training stimulus increases protein synthesis, this does not result in an acutely positive protein balance in the absence of food proteins, leading to the build-up of muscle mass.

However, if you supplement strength training with high-quality food proteins in the necessary amount, this quickly leads to a positive protein balance. This is because the additional food protein further stimulates protein synthesis and ultimately outweighs protein degradation. The body then accumulates the smallest amounts of protein. The sum of these extremely small “protein build-up surpluses” leads to measurably more muscle mass in the long term.


What is responsible for increasing protein synthesis?

Certain (essential) amino acids are responsible for increasing protein synthesis through food proteins. Different protein sources contain these amino acids in different amounts and different compositions; different protein sources influence muscle protein synthesis to vary degrees. But more on that in another article.

In addition to the protein source, the amount of food protein supplied is central to the protein balance increase. Since muscle protein synthesis cannot be increased at will and at the same time excessive amounts of total protein stimulate protein degradation, biological limits are therefore set for effective protein intake. So it makes no sense to add small or excessively high amounts of protein to increase muscle protein synthesis.


Protein intake during the day

A supplemental protein intake during the day (e.B. with increased protein demand due to physical activity or in “unbalanced” diets) thus aims to maintain muscle mass by the increased protein synthesis compensates for the “natural” protein degradation. The central feature here is that just under 10 g of essential amino acids are sufficient for the maximum increase in muscle protein synthesis, but the protein breakdown increases in protein portions > 20-25 g/portion.

Therefore, you should be careful to increase the amount of “high-dose” protein sources with the highest possible proportion of essential amino acids. Thus, it makes little sense to consume protein supplements, which increase protein synthesis to the maximum per serving, based on the high total protein amount (e.g. 40 g per serving) and unnecessarily boost protein degradation.


Protein sources vs. protein synthesis rate

In a revealing study, Tang et al. (2009) investigated the effects of whey protein, soy protein and casein on digestive speed (shown as blood concentrations e..B of essential amino acids depending on the time after protein ingestion), plasma insulin concentration and mixed muscle protein synthesis rate. To this end, they recruited 18 young, healthy men accustomed to muscle training, who, on three different days with sufficient break in between, performed the two exercises knee stretches and leg press until muscle failure (“intense”) (the dormant leg served as an internal control). All study participants consumed either whey protein, soy protein or casein in random order immediately after muscle training, with all protein portions containing approximately 10 g of essential amino acids (EAS).

3 hours after protein intake, the researchers took a muscle tissue sample from both thighs using biopsy needles and determined the mixed muscle protein synthesis rate. Besides, they took blood samples from all study participants 30, 60, 90, 120 and 180 min after protein intake. They tested the blood for the concentration of essential amino acids, insulin L-phenylalanine and L-leucine.


Blood concentrations (“digestion speed”)

While whey protein almost doubled eAS concentration sin for 30 minutes after consumption and soy protein increased the EAS concentration in the blood to almost 1.5 times simultaneously, the EAS blood concentration in casein increased by only about 50%. After 3 hours, EAS concentrations at all protein sources returned to baseline, while casein led to a less abrupt decline than whey protein and soy protein. In terms of L-leucine concentration, whey protein resulted in a concentration increase of almost 3 times as high (measured as an area below the curve) as casein and about twice as high as soy protein. In terms of blood insulin concentration, whey protein was found to increase insulin concentration the most, closely followed by soy protein. In contrast, the blood insulin concentration after casein did not change.


Muscle protein synthesis rate

Taking whey protein and soy led to a stronger increase in muscle protein synthesis rate than casein, both at rest (untrained leg) and after exercise. Besides, the increase after training was greater for whey protein than for soy.


In summary, the following points can be recorded about proteins.

  • Whey protein leads to a stronger increase in amino acid and insulin concentration in the blood after training as soy protein and soy protein again as casein (whey > soy > casein).
  • Whey protein increases the muscle protein synthesis rate more than soy protein, which, in turn, more strongly than casein.
  • The “digestion rate” determines the increase in the rate of muscle protein synthesis (the faster and higher the increase, the higher the increase in the rate of muscle protein synthesis).
  • When the same amount of EAS is administered (approximately 10 g), the protein source with the higher L-leucine content increases muscle protein synthesis the most.


What does this mean for practice?

After the workout, drink about 20 g of whey protein.

Do not consume casein after your muscle training. So do not use milk-based (possibly massively sugared) UHT ready-made shakes. Stir your whey protein powder with water or drink a water-based whey drink. Casein is, therefore, more suitable for protein supply before bedtime.

Therefore, if you cannot or do not want to add whey protein, supplement your soy protein shake with L-leucine or BCAA’s.

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Dr. Med. Raoul Hasert is a specialist in dermatology and venereology. He is a senior physician in Praxisklinik Dr. Hasert.

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