So now we know that the protein part of milk consists of two types: casein and whey. Let’s look at breastmilk to see the ratios of these two proteins. At the start, breastmilk is whey-dominant, with the ratio of whey to casein changing over the stages of lactation. In colostrum (day 1) the whey to casein ratio is 90:10, in mature milk from day 2-3 onwards the ratio is closer to 60:40 (whey:casein) and after eight months the ratio is balanced equally at 50:50. It is these ratios that are used in some infant formula makeup, with the aim to get formula as close to breastmilk as humanly possible.
Whey-dominant formulas are primarily based on whey protein in milk. Whey-dominant formulas have the bonus of being easier for infants under four months to digest than casein-dominant formulas.
Casein-dominant formulas use, largely, curd from dairy milk. While often less expensive, casein-dominant formulas are generally better suited to older infants due to the difficulty younger babies have in digesting casein. Casein is the protein in milk that has also been linked to dairy-based allergies in such babies.
Soy differs from the usual cow’s milk-based infant formulas in two ways: firstly, it doesn’t contain cows’ milk proteins and secondly – being a plant – it doesn’t contain lactose (milk sugar). In some circumstances soy-based formula may be recommended, for example for infants with galactosemia.
While soy-based formulas do not contain lactose, much of the research on lactose intolerances suggests that using a partially hydrolysed cows’ milk-based formula has better outcomes. More on this to follow?
The basis of soy formulas is soybean extracts, and they can be used from birth onwards. Harvested soybeans are processed, removing the outer layer (hull) to create a pulp. In turn, this is further processed to oil and flakes. The flakes of soybeans can be made into soy flour or soy protein isolate and it’s the latter that both formula and some soy milks are made from. Because plant forms of protein are generally considered ‘incomplete’ in that they are missing an essential amino acid (one that the body can’t make), the soy-protein isolate is supplemented with additional amino acids to ensure nutritional bases are covered.
The Australian College of Paediatrics has raised concern over contaminants in soy such as aluminium (used in the extraction process) and also phyto-estrogens (plant estrogens found naturally in soy beans) in formula. Many agencies, when reviewing the available literature on soy-based formulas, suggest that while there don’t appear to be any adverse effects from using soy, there are greater benefits from the use of modified cows’ milk-based formula.
There has been concern raised over the use of soy formula for babies, specifically in relation to phyto-estrogens. Phyto-estrogens have been shown to have a weak estrogenic (estrogen-like) affect. Debate has raised the issue of how this may affect a baby’s reproductive organs. However, current evidence suggests that there is no issue for babies who are fed on soy formula in terms of the plant estrogens found in soy beans. In fact there doesn’t appear to be any effect of soy formula at all on the reproductive organs of babies.
While soy-based formulas provide nutrition for normal growth and development, there are some important factors to consider when deciding on their use. Firstly, if the choice to use soy over dairy is due to a family history of allergies it must be noted that up to 50 per cent of babies who are allergic to cows’ milk protein will also react to soy protein. In fact, if a child is allergic to dairy they are highly likely to also be allergic to soy and/or goats’ milk. Soy-based formulas don’t prevent allergies; in fact there may be concerns that babies fed on soy may have slightly lower immunity. Soy protein can cause intolerance reactions, with up to 40 per cent of infants intolerant to cows’ milk also developing soy protein intolerance. Generally it’s better to use a special low-allergy infant formula such as hydrolysed infant formula. Hence using soy to protect against the development of allergies isn’t generally recommended. Keep in mind before you make any judgment call about allergies or reactions you should gain a medical diagnosis and advice.
NOTE: Soy-based formulas are not suitable for preterm infants due to the difficulty in digesting the components of soy (NHMRC, 2003).
Interestingly, goats’ milk straight from the goat is said to be the closest in composition to human breastmilk, though ‘closest’ doesn’t mean it is in fact similar. Many people use this to suggest that goat’s milk therefore has superior nutritional qualities to other types of milk but this is not true. Once again, goats’ milk-based formulas, like soy, have been used for infants who don’t respond well on dairy or soy-based formula or who have a family history of lactose intolerance. Special mention must be made that fresh goats’ milk is not recommended for infant feeding as it is low in essential nutrients including vitamins A, D, C, B1, B6, B12 and B9 (the latter two being integral to neural development). As a drink it may be offered from 12 months onwards.
Yes, you should follow the guidelines that manufacturers provide and use an age-appropriate formula. As babies grow, their nutrient requirements change and so too does their energy requirement as they get more mobile. Many nutrient needs increase with age, though iodine is one exception. So the move to the appropriate stage (follow-on formula) at the right age helps to ensure your baby gets the range of nutrients for their age at the most ideal level for growth and development.