Association of lower protein infant formula with lower weight at age 2 years

Protein intakes during infancy may impact on overweight and obesity in later life, with lower protein breast milk   being more protective than higher protein infant formulas. This issue was discussed in a previous newswire report Does infant feeding choice affect later obesity? The results of a large randomized clinical study investigating whether higher protein intakes in infancy lead to more rapid gain in weight  and length at age 2 years, has now been published (1).

1138 healthy formula fed infants from 5 European countries ( Belgium, Germany, Italy, Poland and Spain) were randomly assigned to receive either a low protein or high protein infant formula during their first 12 months of life.  619 exclusively breast fed infants were also included in the study for comparison.The lower protein starter formula contained 1.77g protein/100kcals (0.42g/100kJ) and 1.25g protein /100mls while the higher protein starter formula contained 2.9g protein/100kcal (0.69g/100kJ) and 2.05g protein/100mls. Follow-on formula replaced starter after complementary foods were introduced, but not before the start of the 5th month. The low protein follow-on formula contained 2.2g protein/100kcal (0.52g/100kJ) and 1.6g protein/100ml while the higher protein follow-on formula contained contained 4.4g protein/100kcals (1.04g/100kJ) and  3.2g protein/100mls. Breast milk had a variable protein content of 1.2+/-0.2g/100mls. Weight, length, weight for length and BMI were recorded at 3,6,12 and 24 months. Growth was assessed using the 2006 World Health Organisations (WHO) International Growth Standards ( z scores), with the  main outcome being weight and length at 24 months.

58% of infants in the lower protein group, 59% in the high protein group and 51% in the breast fed group were followed to 24 months.  Infants in both the low protein and high protein formula groups consumed the same amount of energy at ages 3,12 and 24 months while at 6 months the lower protein groups had a slightly higher energy intake. The higher protein group consistently consumed more protein than the lower protein group but only until the end of 12 months. The fat intake was lower in the higher protein group while carbohydrate intake did not vary between the groups. 

At 6 months there were differences in weight, weight for length and BMI  between the 2 formula groups with the biggest difference being at 12 months. The higher protein infant formula was associated with higher growth (higher weight, weight for length and BMI) which persisted  after the 12 month formula intervention period. There was no difference in length between the formula groups. As length is associated with lean body mass,  the difference in weight for length and BMI is most likely due to a difference in body fat composition or adiposity. Compared to breast fed infants at 24 months  those fed the higher protein formula had higher z scores for weight, length, weight for length and BMI.  Those infants fed the lower protein formula had similar weight for length and BMI to the breast fed infants but slightly higher weight and length z scores. The protein intake of infants in the lower protein formula group was still higher than those in the breast fed group.

The study shows that  a higher protein infant formula is associated with higher weight, but not length at 2 years of age.  The lower protein infant formula  resulted in lower weight, with growth similarities to that of the breast fed infant. Lowering the protein content of infant formula may be one way to prevent overweight and obesity in children.

Reference:

1. Koletzko B, von Kries et al. Lower protein in infant formula is associated with lower weight up to age 2 y: a randomized clinical trial. Am J Clin Nutr 2009;89:1836-45

Comment.

The Australian New Zealand Food Standards Code regulates the amount of protein allowable in infant formula in Standard 2.9.1(2). For starter formula,the range of protein permitted is 0.45-0.7g/100kJ while for follow on formula it is 0.45-1.3g/100kJ. The low protein starter formula in this study at 0.42g/100kJ would not comply with the current Standard. Protein is higher in infant formula compared to breast milk as it is of a lower biological value and the increased amount is designed to ensure all the  essential amino acids are met. It is now timely to take a closer look at permitted protein levels in infant formula.

Reference:

2. FSANZ. Australia New Zealand Food Standards Code,  Standard 2.9.1 Infant Formula Products www.foodstandards.gov.au