Thursday, 25 June 2015

What about soy-based formula?

There are many articles out on the web that talk about soy milk and babies. I'll try to explain a bit behind the science of it all. 

We are told that soy-based formula is unsuitable for most infants, but why?

If your baby has been prescribed a soy based formula, please do not discontinue it, and discuss any concerns with your doctor

What is soy milk?

Soy milk is made by soaking dried soybeans in water and grinding them. Soy is one of the complete sources of dietary protein (meaning it contains all the essential amino acids), and soy milk has comparable amounts of protein to cow's milk. 

The need for soy based formula?

Soy-based formula (SBF) has been around for many years. In fact, the first soy-formula appeared on the markets in the 1920s. Its presence came about due to the need for alternatives to cows milk formula.  Modern soy formula is formulated to meet the nutritional requirements of babies, and research supports this. Little difference has been found, for example, between the growth of infants fed on cow's milk based and soy-based formulas. SBFs subsequently were preferred by some parents, due to being vegetarian, but they also have a role in the management of many diseases:

"[Soy-based formula is] commonly used in infants with immunoglobulin E–mediated cow’s milk allergy (at least 86% effective), lactose intolerance, galactosemia, and as a vegetarian human milk substitute." [1]

For some time, SBFs were the only suitable substitute in the management of CMA, as a result, millions of babies have been fed soy-based formula over the years with few problems into adulthood. 

What is different about soy?

Soy contains compounds called isoflavones. Some isoflavinoids are referred to as phytoestrogens as they have effects via oestrogen receptors. Though isoflavones have weak activity at oestrogen receptors, they can be present in relatively high concentrations in infant SBFs [2]. 

Concerns have been raised about the safety of phytoestrogens on the developing reproductive system, and other hormone sensitive tissues. Theoretically, there are potential adverse effects on puberty onset, the development of hormonally sensitive cancers, and bone development. The risks of excess oestrogens on the development of boy's gonadal tissue is a concern as well. However, there is very limited data, and the data that does exist shows similar outcomes with babies fed cow's milk based formula [3]. Despite the lack of evidence, many countries have recommending restricting the use of SBF based on animal and cell studies [4].

What about lifetime risk? Soy-based foods (milk, tofu etc) have a long, safe, track record in human history, especially in Asian countries. So, lifetime exposure to soy is not a new concept. However, the introduction of SBFs is a relatively new phenomenon, and little is known about the long term health consequences on infants fed on it from an early age, combined with a Western lifestyle and diet. 

Soy allergy

Soy milk in itself can cause allergies. Overall, the incidence on its own is low, probably at, or around 1%. Let's look at what one research paper said:

"The incidence of soy allergy in soy formula-fed infants is comparable to that of CMPA in cow’s milk formula-fed babies. Adverse reactions to soy have been reported in 10–35% of infants with CMPA, regardless of whether or not they were positive or negative for specific IgE antibodies for CMP." [6]

There appears to be  degree of cross-reactivity between CMA and soy allergy, rendering SBF an unviable alternative to many children with CMA. Because of this high cross-over rate, infants with CMA are now advised to have hydrolysed formula instead. 


Admittedly, there are circumstances where soy milk may be the preferred option for some babies, such as in the case of some hereditary diseases [5], or infants who refuse the hydrolysed or amino acid formula preparations, where the risk-benefit dynamic may alter. In the meantime, with hydrolysed formulas easily available nowadays, the theoretical risks associated with SBFs can be avoided. 

Some links for articles on soy milk:

British Dietetic Association factsheet on suitable milks.

References:[1] Safety of soy-based infant formulas containing Isoflavones: The clinical evidence. Merrit RJ & Jenks BH. J Nutr (2004); 134(5) 1220S-1224S[2] Concerns for the use of soy-based formulas in infant nutrition. Canadian Paediatric Society Paediatr Child Health. 2009 Feb; 14(2): 109–113.[3] Soy-based formulae and infant growth and development: A Review. Mendez et al (2002) J Nutr; 132(8) 2127-213[4] The health implications of soy formula. Badger TM et al (2009) Am J Clin Nutr; 89(5) 1668S-1672S[5] Use of Soy Protein-Based Formulas in Infant Feeding. American Academy of Paediatrics. Pediatrics (2008); 121(5) 1062-1068[6] Guidelines for the diagnosis and management of cow's milk allergy in infants. Vandenplas Y et al, Arch Dis Child 2007; 92:902–908

No comments:

Post a Comment