Proteins, Peptides and Amino Acids: Role in Infant Nutrition
Proteins are the main building blocks of the body. They are polymers, composed of 30 or more amino acids. Twenty different standard amino acids combine to form the proteins. Some amino acids are essential diet components, since they are not synthetized by human metabolic processes.
Proteins are present in and vital to every living cell. They are essential for healthy growth and development and also influence major functions of the body (Figure 1). They can influence metabolic parameters (weight gain and adipogenic activity), presence of beneficial bacteria in the gut, risk of developing atopic dermatitis, digestive functions and renal system.
The infant’s first year is a critical time of rapid growth and development; this rapid growth must be supported by a high rate of protein synthesis. Infant nutrition requirements are primarily satisfied by a single and highly specific food source: breast milk. The composition of breast milk is the gold standard for estimated total protein and essential amino acid requirements during infancy .
Both total protein content and concentrations of individual proteins in human milk change throughout the first year of lactation to fulfill the needs of the infant. Milk proteins are also a source of biologically active peptides, released by gastrointestinal digestion and having a positive impact on body functions and ultimately promoting health benefits .
Infant formulas have been designed for infants who cannot be breastfed. These infant formulas need to be similar to breast milk in their composition but also in functional outcomes, to insure appropriate growth, optimal development, maturation of immune system, programming of the metabolic system… . They have been evolving throughout decades along with the scientific knowledge. Protein sources and processes have been optimized to provide very similar amino acid profiles as found in breast milk. More recently, clinical data showed that lower protein content in infant formula has a long-term preventive impact on BMI and obesity risk .
In addition to guaranteeing healthy growth and development of bottle-fed infants, specific infant formulas have also been designed for specific needs, by modifying their protein component.
As an example, three different types of infant formulas have been designed for management of cow’s milk allergy (affecting around 5% of infants): partially hydrolyzed, extensively hydrolyzed or amino acid based infant formulas (Figure 2). Allergy is triggered by protein components; one way to decrease allergenicity of proteins is to modify their conformation and/or structure responsible for the allergy, by cutting protein into peptides which are not able anymore to trigger an allergic reaction.
Some partially hydrolyzed whey based infant formulas have been clinically proven to prevent atopic dermatitis in infants  and a first ever FDA claim has been granted for their use in infants at risk of allergy. The specific process leading to partially hydrolyzed infant formulas leads to a reduction in allergenicity of the milk proteins and generates specific immunomodulatory peptides allowing the beneficial effect.
Extensively hydrolyzed infant formula are resulting from a different production process leading to very short peptides, having almost no allergenic properties anymore. These infant formulas have been designed for therapeutic application, offering a solution to reduce allergy symptoms in infants allergic to cow’s milk proteins.
Finally, in case of severe allergic reaction to cow’s milk proteins, only amino acid based infant formula are able to decrease symptoms because they are totally devoid of allergens.
In conclusion, proteins provided via breast milk or infant formula are essential components of infant’s diet and therefore the specific quality, quantity and conformation of these proteins are essential for a safe growth and development.