The short answer is enough protein, but not too much.
The long answer is as follows. Protein is of special nutritional importance during infancy, as protein is present in all living cells and it contributes to an structural development during infancy (e.g. laying down new tissues and strengthening them), as well as having important functional roles (e.g. proteins are incorporated into enzymes, hormones, neurotransmitters and a whole range of other important functional compounds).
All mammals produce milk to feed their little ones, but there are differences in the nutrient compositions between various mammalian milk types. For example, human milk has around 1 gram of protein per 100 mL milk. Compare this to cow’s milk, which has more than three times this amount, at around 3.4 grams protein per 100 mL.
Currently, infant formula are formulated to contain much less protein than ordinary cow’s milk, to approximate the lower protein levels seen in human breast milk, but there remain differences in protein levels, even between infant formula.
This is important, because recent research highlights that higher protein intakes during infancy may increase the risk of overweight and obesity in a child when they reach school age and beyond.
This is different in adults, where higher protein diets have been shown to have benefits, such as keeping us fuller for longer and reducing hunger pangs between meals so that we eat less, which may help us to lose body fat and gain muscle when combined with exercise… but not for babies and little ones.
The evidence for this starts with early observational studies, which identified that babies and toddlers (up to 2 years of age) with rapid weight gain had an increased risk of obesity later in life. Furthermore, those babies who were breastfed – and the longer the better – were far less likely to have such rapid weight gain and consequently had a lower risk of being overweight or obese years later. The magnitude of difference was in the range of a 15-25% lower rate of obesity in breastfed children, so the reason for the difference was one worth exploring.
While infant formula protein levels are much lower than dairy milk protein levels per 100 mL (in order to approximate breast milk protein levels), they still have higher protein levels than breast milk, just to make sure babies get enough of all the good proteins needed for growth. However, the net result of this is that exclusively formula fed babies typically consume more protein than breastfed babies during their first two years.
This observation lead researchers to hypothesise that the higher protein intakes could be driving the rapid weight gain observed in formula fed infants. The next step was to test this hypothesis, which is exactly what researchers from the European Childhood Obesity Project did…
Researchers compared three groups of infants. One was a group of infants who were breastfed exclusively for at least 3 months (the observational reference group). The other two groups were made up of formula fed babies, who were randomly allocated to receive either: 1) a conventional higher protein formula; or 2) a lower protein formula that was closer to that found in breast milk (although still slightly higher).
So, here’s what they found. From 6 months of age, the higher protein formula group had significantly higher weight, weight-for-length and body mass index (commonly known as BMI) compared to the lower protein formula group, but there were no differences in the length of babies by 12 months (so, babies were heavier, but not shorter). By 6 years of age, the differences between the groups were marked, with the higher protein group showing far higher BMI values and rates of overweight compared to the breastfed group.
The lower protein formula fed children were far closer to the breastfed group, such that by 6 years of age there was no significant difference between the groups. Thus, a lower protein formula normalised this risk in line with breastfeeding.
This research adds to our knowledge that “breast is best”. We have a fantastic uptake of breastfeeding in Australia, with 96% of mums choosing to do so from birth. However, there is a rapid drop off in rates, such that by 3 months only 39% of babies are exclusively breastfed and by 5 months, only 15%. Greater support from lactation consultants and other health professionals (as well as societal shifts in attitudes to breastfeeding) could significantly boost these rates, as well as the knowledge that breastfeeding is a skill which takes time for both mums and bubs to learn.
However, breastfeeding is not always possible or for a myriad of reasons, is not the choice made by a family. Modern formulas are improving all of the time and offer a safe alternative.
For now, parents can compare the protein content of currently available formulas and choose those at the lower end of the protein range. At the same time, regulation change is required, to allow even lower protein formulations to be produced.
Finally, we need more research to understand the implications of a higher protein intake beyond infancy and into the first few years of life. Until we understand more, it seems prudent to avoid excessively high protein intakes and instead focus on a broad range of whole foods and cutting back on the amounts of discretionary foods with a high energy-density and low nutrient-density.
See our Toddler section for healthy nutrition tips for toddlers.