Protein is critical for development—virtually every structure in the human body contains protein as its core building block. If protein levels it a baby's diet are too low, growth and development may be hindered. On the other hand, infants can be given too much protein during development.
Excessive protein can cause a number of unwanted effects, but the greatest risk appears to be obesity later in life. We review the literature on safe and effective protein levels for infants.
The risks of too little protein are obvious; the body needs sufficient protein to build itself and function properly. However, the medical community has only recently begun to identify the risks of too much protein in the infant diet. Over the past decade, physicians and researchers identified that breast-feeding leads to lower rates of obesity later in life than formula diets.
Human breast milk contains less protein than most commercial formula preparations.
Breast-feeding infants receive about 9 to 10 g of protein per day between the ages of 3 to 6 months while those consuming formula received 14 to 18 g of protein per day.
Not surprisingly, formula fed babies gain more weight during the first year of life; however, weight gain during the first year of life is one of the strongest predictors of obesity later in life.
Increased protein intake does not simply provide the structural building blocks for larger babies, but also seems to stimulate growth hormones in infancy, later childhood, and early adulthood.
Taken together, high-protein diets during the first year of life appear to be strongly linked to lifelong obesity. Moreover, infants fed high-protein formula were 2.4 times as likely to be obese by the time they reached school age than those fed a low protein formula.
In these studies, babies received cow milk-based infant formula and then follow-on formula. Low protein cow milk-based infant formula (IF) contained 1.77 g of protein per 100 kcal and follow-on formula (FOF) containing 2.2 g of protein per 100 kcal. Higher protein formula contained 2.9 and 4.4 g of protein per 100 kcal, respectively. Aside from protein content, the rest of the nutrients were the same in both groups. Children fed breast milk or low protein formula appear to have very similar risks of obesity, while the risk of obesity among children fed a high protein formula is considerably higher.
Based on these results and related studies, the European Food Safety Authority (EFSA) recommends the following nutritional content for full term babies.In practical terms, the EFSA recommends that milk protein content in both infant and follow-on formula should be limited to a maximum of 2.5 g/100 kcal.For isolated soy protein and hydrolyzed protein, the maximum protein recommended content is 2.8 g/100 kcal.
Protein requirements for preterm infants or infants who are acutely ill at the time of birth, are higher than they are for healthy, full-term infants. This is understandable since the body requires additional energy when dealing with critical illness and/or the stresses of prematurity. Research in this area is somewhat scarce and this prevents firm recommendations.
Suggestions are premature infants who are born with body weights less than 2.5 kg should probably consume diets between 3 to 4 g of protein per kilogram of infant body weight per day to achieve a healthy body weight and to overcome prematurity. This level of protein intake accelerates weight gain.
Often preterm infants are given "post-discharge formula" or nutrient-enriched formula when they leave the hospital; however, there is limited evidence to suggest that this actually results in improved growth rates. This increased protein could conceivably result in obesity later in life.
Breast-feeding is still the best option for both full term and preterm infants since it provides suitable amounts of protein along with many other nutritional benefits. When breast-feeding is not an option, infant and follow-on milk protein formula should contain between 1.8 and 2.5 g of protein per 100 kcal. Isolated soy protein and hydrolyzed protein formula, should contain no more than 2.8 g/100 kcal of protein. These formulations provide sufficient, but not excessive amounts of protein for developing infants.
Premature, low birth weight infants may require additional protein during hospitalisation. While it is too early to determine if premature infants need nutrient-enriched formula at discharge from the hospital, current evidence suggests that non-fortified breast milk is sufficient and formula with low protein amounts may be acceptable.