Proteins are made up from amino acids. Proteins from the diet are broken down during digestion into amino acids and are then reassembled by the body into the proteins that it needs.
Over 20 of these amino acids are important to the body and some of them can be made by it. These are called Non-essential amino acids. They include alanine, aspargine, aspartic acid, glutamic acid, glutamine, glycine, proline, serine and tyrosine.
Those that cannot be made by the body and need to be got from food sources are called Essential amino acids. Those needed in infancy include tryptophan, cystine, arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tyrosine and valine.
Growth is particularly rapid during the first 6 months of life when infants double their birth weight and requirements for protein compared to bodyweight are at their highest. Proteins are found throughout the body and are needed both for growth and to function. Some examples are:
- · muscle growth and formation of organs and blood
- · energy provision
- · haemoglobin transport
- · digestion and metabolism
- · tissue repair
- · immune system development
Although protein is vital for development, excess protein can be a problem as it is not stored but excreted through the kidneys. This increased workload can be a problem for the developing kidneys.
Too large an intake of protein can lead to rapid weight gain1 and undesirable weight gain in early infancy is linked to obesity in childhood and young adulthood2.
Unlike adults, who can get protein from a varied diet, very young babies can only do so from either breast milk or infant formula. It is important, therefore that the milk formula they drink, like breast milk, has the right protein composition.
There are two types of protein in breast milk. Their proportions are 40% casein and 60% whey. Casein produces curds and tends to stay longer in the stomach. Whey is more soluble and is easier to digest. Alpha-lactalbumin is an alpha protein found in whey. Alpha protein makes up 27% of mature breast milk3,4. Alpha proteins contain a high proportion of essential amino acids. Breast milk contains 33% other whey proteins but no beta proteins3,4.
Many infant formulas have the same proportions of casein to whey as breast milk but tend to have more beta proteins than alpha proteins in the whey3,4. It is believed that this can contribute to cow’s milk protein intolerance5,6.
The proportion of a-lactalbumin in Ronalac is 20%. This compares well with the 28% found in breast milk and means there is only a minimal load on the developing kidney. Conventional infant formulas are around 11% while cow’s milk is 4%. This close profile with breast milk helps make Ronalac a good choice for bottle fed babies and those who are combination feeding.
1. Koletzco B, et al. Lower protein in infant formula is associated with lower weight up to age 2 years: a randomized clinical trial. Am J Clin Nutr 2009; 89: 1-10.
2. Stettler N, et al. Infant weight gain and Childhood Overweight Status in a Multicentre, Cohort Study. Pediatrics Vol 109, No 2, 2002.
3. Lien EL, et al. Growth and safety in term infants fed reduced – protein formula with added bovine alpha-lactalbumin. Journal of Pediatric Gastroenterology and Nutrition 2004; 38: 170-16.
4. Lien EL. Infant formulas with increased concentrations of alpha-lactalbumin. Am J Clin Nutr 2003; 77(6): 1555s-1558s.
5. Selo, et al. Allergy to bovine b-lactoglobulin: specificity of IgE to tryptic peptised. Clinical and Experimental Allergy, 1999, 29: 1055-1063.
6. Heine WE, et al. The importance of a-lactalbumin in infant nutrition. Journal of Nutrition 1991; 121 (3): 277-283.