And is undenatured protein really better for muscle growth in sports?

Scientific review of available literature from December 2018

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This question is regularly raised on many popular bodybuilding resources. A number of sources attribute to undenatured protein anticancer, immunomodulatory, antioxidant activity, improvement of blood sugar levels and a positive effect on protein synthesis in athlete's muscles [1,2,3], and of course, according to all these indicators, "normal" denatured protein shown in a worse light. It is not surprising that such information is actively discussed on forums [4,5], and manufacturers produce special series of protein with the appropriate mark on the package [6].

How justified are such statements? Let's understand each other.

Protein and its structure

A protein, also known as a protein or a polypeptide, is a chain of amino acids connected by peptide bonds [7]. This is called the primary structure of the protein.

Fig. 1 The primary structure of the protein

Apolipoprotein C1, which is involved in cholesterol metabolism, consists of 57 amino acids [8], while titin, one of the important proteins of human muscles, has a length of about 35,000 amino acids [9].

p align="justify"> The next level of protein molecule organization is the secondary structure, which is stabilized by another type of bonds - hydrogen bonds [7]. Within the framework of the secondary structure, connections between adjacent amino acids are considered.

Fig. 2 Transition from primary to secondary protein structure [10]

When it is necessary to consider the method of assembly of the entire protein molecule, including the connection between relatively distant amino acids, we are talking about the tertiary structure. Several types of chemical bonds are involved in maintaining such a structure - hydrophobic, hydrogen, electrostatic, etc. [11].

Fig. 3 Tertiary structure of the protein. Ovalbumin, one of the chicken egg proteins [12]

Some proteins are a complex of several protein chains (in the case of so-called subunits), which are united together in such a way that they perform their functions. To describe such complexes, the term "protein quaternary structure" is used. An example of such a complex is hemoglobin, which carries oxygen in the blood and consists of 4 subunits of 2 types, 2 subunits of each type.

Fig. 4 Quaternary structure of hemoglobin. 4 subunits are highlighted in different colors [7]

Proteins become functional only after the formation of the three-dimensional structure is completed, when all the necessary chemical bonds are established and the protein acquires its characteristic appearance.

Protein denaturation

In the strict biochemical sense, denaturation refers to the loss of a protein's functional properties due to a violation of its three-dimensional structure. Denaturation does not necessarily mean fully unfolding into a chain and adopting a disordered structure, there are many intermediate states. Sometimes a critical violation of literally several connections.

Fig. 5 Protein denaturation [14 with changes]

However, it is important to note that during denaturation, the primary structure of the protein does not change, that is, the peptide bonds remain intact and the protein is not split into fragments. The length of the molecule, amino acid composition, etc. are preserved.

Denaturation can occur under the influence of high temperatures, acids, alkalis, etc. [7]. A classic example of denaturation is the change in the appearance of the protein part of a chicken egg after cooking, and it is obvious that such denaturation is irreversible at home [13].

However, in some cases, the restoration of the three-dimensional structure of the protein is still possible, and this process is called renaturation. The property of renaturation is used in many laboratory methods of working with proteins.

If the primary structure of the protein is still broken, then the so-called destruction has occurred [15].

Thus, denaturation means only a change in the arrangement of the protein molecule in space.

Proteins and digestion

Ok, the athlete drank a protein shake or ate a piece of meat. Now consider what happens to proteins from similar products in the gastrointestinal tract. The entry of food into the stomach stimulates the secretion of the hormone gastrin, which, in turn, increases the secretion of hydrochloric acid (HCl) and pepsinogen, the precursor of the enzyme pepsin, which will break down proteins from food [7]. As you can see, an acidic environment has formed in the stomach (pH 1.0-2.5, such values correspond to very high acidity), and this environment is a factor that contributes to the denaturation of the protein molecule.

Are there proteins that are able to withstand such an acid effect? Yes, there is. For example, some proteins of cells of the stomach itself [16]. However, lactalbumin, casein, ovalbumin and other common proteins from food are not acid-resistant and are subject to denaturation. Actually, after denaturation, the peptide bonds, which are primarily hidden in the depths of the three-dimensional structure, become available for attack by various enzymes, which will bind these bonds. Among such enzymes, pepsin from gastric juice has already been mentioned. After such processing, the food enters the small intestine, where other enzymes - trypsin, chymotrypsin, carboxypeptidases, and aminopeptidases - carry out digestion. The difference between these enzymes lies in the combinations of amino acids, the bond between which these enzymes destroy.

Here, in the small intestine, digestion products are absorbed. These are single amino acids or short peptides (usually 2-4 amino acids long) [17,18,7].

As you can see, the absorption of a complete large protein molecule, which could perform immunomodulatory and other functions mentioned at the beginning of the article, does not occur - the protein is split into short fragments.

Some proteins, for example, keratin (one of the proteins of hair and nails) are still not completely digested [7], pass through the intestines further and leave the body. There is no special absorption of them either.

However, there is some difference between digestion of denatured and undenatured protein. Thus, it was shown on laboratory animals [19] that digestion of raw meat, compared to heat-treated meat, took more time and required more body resources. This difference is explained by protein denaturation under the influence of high temperature, for example, during cooking.

Proteins from the lines of sports nutrition, such as casein, whey, egg protein and others, are more quickly absorbed by the human body after processing by hydrolysis [20, 21, 22]. Hydrolysis includes both denaturation and destruction, that is, splitting the protein into shorter fragments, but destruction is beyond the scope of this article.

Thus, there is a relationship between the degree of protein processing and the speed of its assimilation [23]. Undenatured protein will take longer to digest. However, it is much easier to achieve the gradual absorption of amino acids and short peptides - by choosing the appropriate type of sports nutrition. Thus, whey protein is absorbed relatively quickly, and casein is absorbed slowly [24]. At the same time, the body will not have to spend energy on additional processing of the food product. The same resources can be directed to the most important goals - building the athlete's muscles.

Some reasonable advantages of undenatured protein for a bodybuilder are not mentioned in modern scientific literature.

At the same time, protein denaturation occurs within the technological processes of sports nutrition production [25, 26] and, as we can see, is beneficial for further assimilation of such proteins by the athlete.

Conclusion of the comparison of denatured and undenatured protein

Summing up, protein denaturation increases the rate of its breakdown and saves the body's energy. Based on this, in bodybuilding it is clearly more profitable to use denatured protein, which is included in the usual sports nutrition products. The range of such products is very wide, and the cost is lower compared to specific products with undenatured protein.

Literary sources

https://lifespa.com/benefits-undenatured-whey-protein-powder/
https://renewingallthings.com/lifestyle/diet/protein-powder-causing-inflammation/
https://dailyfit.ru/pitanie-i-dieta/syvorotochnyj-protein-vsya-pravda-o-nem/
https://forum.bodybuilding.com/showthread.php?t=116059&page=1
https://forum.bodybuilding.com/showthread.php?t=140124283&page=1
https://medium.com/@wheyproteinpowderreviews/best-non-denatured-whey-protein-powders-from-grass-fed-cows-28168a04a655
Nelson D, Cox M. Lehninger principles of biochemistry. 7th ed. New York: WH Freeman; 2017.
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http://oasys2.confex.com/acs/228nm/techprogram/P773650.HTM
Syvolob A. Molecular biology. Kyiv: Publishing and Printing Center "Kyiv University"; 2008.
http://www.rcsb.org/structure/1OVA
https://onlinelibrary.wiley.com/doi/abs/10.1002/cbic.201402427
http://www.biosciencenotes.com/denaturation-of-protein/
Berg J, Tymoczko J, Stryer L. Biochemistry. Basingstoke: WH Freeman & Co Ltd; 2006.
Thangarajah H, Wong A, Chow D. Gastric HK-ATPase and acid-resistant surface proteins. American Journal of Physiology-Gastrointestinal and Liver Physiology. 2002; 282 (6): G953-G961.
Digate Muth N. Sports Nutrition for Health Professionals. 1st ed. FA Davis Company; of 2014.
Spano M, Kruskall L, Thomas D. Nutrition for sport, exercise, and health. 1st ed. Human Kinetics; 2017.
Boback S, Cox C, Ott B. and others. Cooking and grinding reduces the cost of meat digestion. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. 2007; 148 (3): 651-656.
Calbet J, Holst J. Gastric emptying, gastric secretion and enterogastrone response to administration of small proteins or their peptide hydrolysates in humans. European Journal of Nutrition. 2004; 43 (3): 127-139.
Manninen A. Protein hydrolysates in sports nutrition. Nutrition & Metabolism. 2009; 6 (1): 38.
Lockwood C, Roberts M, Dalbo V. et al. Activity of Hydrolyzed Whey versus Other Whey Protein Supplements on Physiological Response to 8 Weeks of Resistance Exercise in College-Aged Males. Journal of the American College of Nutrition. 2016; 36 (1): 16-27.
Jager R, Kerksick C, Campbell B. et al. International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition. 2017; 14 (20).
Driskell J. Sports Nutrition: Fats and Proteins. CRC Press; 2007.
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https://patents.google.com/patent/US4421770A/en

Scientific review of available literature from December 2018