The importance of proteins

While carbohydrates and lipids constitute the preferred energy substrate, proteins perform a structural and plastic function of paramount importance. They represent the molecular framework of the organism, essential for proteogenesis, myofibril repair, and enzymatic regulation (Phillips, 2014). In sports nutrition, their role is not limited to muscle mass: they are the catalysts of metabolic adaptation to exercise.

Molecular Architecture and Classification of Proteins

Definition and Peptide Bond

A protein is a complex macromolecule resulting from a sequence of amino acids linked by peptide bonds. This covalent bond is formed by dehydration between the carboxyl group of one amino acid and the amine group of the next. The spatial configuration of these chains (primary to quaternary structures) defines the biological function and thermal stability of the protein (Tessari et al., 2016).

Classification by Chain Length

• Oligopeptides: Less than 10 amino acids. This is the case for bioactive peptides like Carnosine.
• Polypeptides: Between 10 and 100 amino acids (e.g., insulin, a peptide hormone of 51 amino acids).
• Proteins: More than 100 organized amino acids. Their high molecular weight requires complete gastric and pancreatic proteolysis to release free amino acids and absorbable small peptides.

Amino Acids: The Building Blocks of Life

There are 20 so-called "proteinogenic" amino acids. Their biological value depends on their profile of essential amino acids (EAA), which the organism is unable to synthesize de novo from carbon or nitrogen precursors (Wolfe, 2017).

Essential Amino Acids (EAA)

They must be provided by the diet to avoid blocking protein synthesis according to Liebig's Law of the Minimum:

• BCAA (Branched-Chain Amino Acids): L-Leucine, L-Isoleucine, L-Valine. Leucine is the main allosteric modulator of the mTORC1 complex (Tang et al., 2009).
• Other EAA: L-Lysine, L-Phenylalanine, L-Threonine, L-Methionine, L-Tryptophan, L-Histidine.

Conditional and Functional Amino Acids

Certain amino acids become essential during periods of metabolic stress, growth, or pathology (e.g., L-Arginine for endothelial function, L-Glutamine for intestinal barrier integrity). Non-essential amino acids (L-Alanine, L-Glycine, etc.) complement the nitrogen pool essential for homeostasis (Wu, 2009).

Conclusion: The Impact of Proteins on Athletic Homeostasis

From Structural Role to Cell Signaling

Proteins do not just repair tissues; they act as ligands and signaling molecules. Leucine, for example, triggers the phosphorylation cascade necessary for myofibrillar hypertrophy. Without a positive nitrogen balance, the organism shifts into a catabolic state that is detrimental to performance and immunity (Morton et al., 2018).

Optimization of Protein Synthesis

For the athlete, the quality of the protein (measured by the DIAAS score) is as crucial as the raw quantity. An expert approach is to saturate the amino acid pool at key moments (peri-workout window) to transform each session into a real and lasting growth signal.

1. Phillips (2014) - A brief review of critical processes in exercising human skeletal muscle.
2. Tang et al. (2009) - Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis.
3. Wolfe (2017) - Branched-chain amino acids and muscle protein synthesis in humans: myth or reality?
4. Wu (2009) - Amino acids: metabolism, functions, and nutrition.
5. Morton et al. (2018) - A systematic review of the effect of protein supplementation on resistance training-induced gains in muscle mass.