There is a general understanding that the current protein content in infant formulas exceeds infant requirements, but the optimal protein content of infant formulas is still controversial. Several guide lines and experts have made recommendations for the protein level in infant formulas, which generally agree on a minimum value.
- The European Society of Pediatric Gastroenterology, Hepatology and Nutrition (ESPG HAN) recommend a range of 1.8-2.8 g/100 kcal.
- The committee on nutrition of the American Academy of pediatrics and the United States Food and Drug Administration (FDA) recommend a range of 1.8 –4.5 g/100 kcal.
- The upper limit of 4.5 g/100 kcal has been criticized as being much too high (3).
- Fomon has recommended a minimal amount of protein in infant formulas of 2.2 g/100 kcal for infants younger than three months and 1.6 g/100 kcal for infants older than three months. No precise recommendation is given for the whey/casein ratio (2).
In order to meet the demands for a low protein infant formula when formulating a low protein formula from cow’s milk protein, the protein ingredients used must be of high nutritional value. This requires protein ingredients with good digestibility, which closely mimics the amino acid profile of human milk.
Effects of an Early High Protein Intake
Protein intake of formula-fed infants has been reported to be 55-80 percent higher compared to the intake of breast-fed infants, correspondingly the energy intake is 10-18 percent higher (4). Evidence is accumulating that an early high protein intake confers several adverse health effects in later life.
Several studies have looked at the different effects of protein intake on growth and development in breast-fed and formula-fed infants. These studies have shown that the growth of human milk-fed infants is different from the growth of formula-fed infants particularly for weight. Growth is fastest in the first few weeks after birth. This period may therefore be a key window for adverse programming (5). Early postnatal over nutrition has been shown to program adiposity in animal models. For instance, it has been shown that mice given a high-protein diet during the suckling period were more obese and had a lower life span than mice given a low-protein diet (6). Furthermore, epidemiological studies show that high postnatal weight gain might be a risk factor for later metabolic syndrome diseases such as hypertension, diabetes and coronary heart disease. It has been shown that the risk of overweight and obesity for formula-fed infants was increased in proportion to weight changes during the first week of life (7).
Currently, the EU Childhood Obesity Programme which has 1000 infants enrolled in five European countries is studying the effect of protein intake the first year of life on growth effects and obesity. It is the hypothesis that a high early protein intake may enhance weight gain in infancy and the risk of later obesity (the “early protein hypothesis”). Preliminary results from the EU Childhood Obesity Programme indicate that low-protein content in infant formulas may have metabolic, endocrinal and developmental benefits for infants (4). The mechanism may be that concentrations of hormones, metabolites and neurotransmitter s during critical periods of early development will program disease risk in adulthood.
Benefits and Composition of Low Protein Formulas
Typical infant formulas contain less than half the α-lactalbumin of human milk and significant amounts of β-lactoglobulin. Cow’s milk α-lactalbumin has an amino acid composition that is closer to the essential amino acid requirements of infants than other milk fractions. Bovine α-lactalbumin has the highest level of tryptophan and cysteine of all bovine casein and whey fractions.
An α-lactalbumin enriched and β-lactoglobulin reduced infant formula therefore allows for a lower total protein content due to higher levels of essential amino acids. In vivo studies show that formulas rich in a-lactalbumin have high protein quality and are well utilized by infants (8).
In addition to being an excellent source of amino acids, α-lactalbumin is positively related to several physiological effects, such as antimicrobial activity, enhanced immune function, prebiotic function and increased trace element absorption (9).
Furthermore, a low protein modified formula will give a better balance between tryptophan and other large neutral amino acids which is important for neurotransmitter synthesis, brain development and sleep.
Other benefits of a reduced protein-load and the following changed amino acid composition can be improved digestion and thereby less adverse events such as colic, irritability and constipation.
The digestive capacity may be somewhat reduced in early life due to a less acidic gastric environment and a not fully developed enzymatic activity. α-lactalbumin enriched formulas have shown to be associated with better tolerance than typical whey dominant formulas (1).
1. E.L. Lien, A.M. Davis et al., J of Pediatr Gastroenterol Nutr., 38(2), pp. 170-176 (2004).
2. N.C.R. Räihä, A. Fazzolari-Nesci et al., J Pediatr Gastroenterol Nutr., 35(3), pp. 275-281 (2002).
5. A. Singhal, “Does Breastfeeding Protect from Growth Acceleration and later Obesity?, Issues in Complamentary Feeding”, Karger, 60, pp. 15-29 (2007).
6. S.P. Garnett, C.T. Cowell et al., Int J Obes Relat Metab Disord., 25, pp. 1667-1673 (2001).
7. E.E. Ziegler, “Growth of Breast-Fed and Formula-Fed Infants, Protein and Energy Requirements in infacy and childhood”, Karger, 58, pp. 51-63 (2006).
8. B. Lönnerdal, E.L. Lien, Nutr Rev., 61(9), pp. 295-303 (2003).
9. O. Sandstöm, B. Lönnerdal et al., Am J Clin Nutr., 87, pp. 921-928 (2008).