5 common concerns about soy and your child’s health

5 common concerns about soy and your child’s health

Soy and soy food products have been gaining increasing popularity, thanks to the promotion of plant-based diets, veganism or just as a part of an overall healthy lifestyle. Every day, it’s easier to find soy foods like milk and yogurt, or fermented products, such as miso, tempeh, and tofu in the supermarket.

Soybeans have been part of traditional Asian diets for centuries, undergoing minimal processing. In Western societies, soybeans have been used increasingly more and more in livestock feed as a source of protein and in wide applications within the food industry in the form of soy flours and protein concentrates – from breads, bakery products, fillers within meat products, vegetarian meat substitutes, and oils/margarines.

Photo credit: https://examine.com/nutrition/is-soy-good-or-bad/

However, despite all the potential and/or claimed health benefits like cholesterol reduction, prevention of heart disease, and cancer, soy has also received a lot of negative press. There are still many concerns about soy safety in children, particularly the reproductive organs during their growth and development. Parents often ask questions like “is my male child going to have reduced testosterone or his sexual organs be affected by soy consumption?” “And what about a soy-based infant formula, if the parents follow a vegan lifestyle, is it good for the baby?”

In this blog, I’m going to explore the evidence behind some of the most common nutrition myths and questions about whether soy is healthy for babies and children, based on  scientific literature. I must stress here that the gold standard are randomised controlled trials that have large enough sample sizes to be statistically significant. When a number of these types of trials are analysed together, into a meta-analysis, solid evidence based information and conclusions can be drawn on.


Not only is soy an excellent source of protein, which makes them great for vegetarians, or those looking for meat and milk substitutes, it also provides many other beneficial nutrients, like unsaturated fatty acids, B vitamins, fibre, iron, calcium, zinc and other bioactive compounds. Flavonoids exert an anti-oxidative effect which may protect against cancer and cardiovascular disease.

Soy, however, is also known to have very high “anti-nutrient” content, containing tannins, phytates, trypsin inhibitors and goitrogens which can interfere with the digestion and absorption of various vitamins/minerals and proteins. Many of these anti-nutrients, however, are vulnerable to processing, such as soaking, boiling, roasting, and heat, so in this way, can be reduced by various cooking and processing methods. Phytic acid can be significantly reduced by consuming traditionally fermented soy products like miso, natto, soy sauce and tempeh. Isoflavones can also be reduced if a high isoflavone containing product such as a soy protein powder has been made using an alcohol wash.

Photo credit: https://examine.com/nutrition/is-soy-good-or-bad/

Interestingly, there is some evidence that suggests that gut bacterial flora may determine soy’s health effects on the body. Soy contains two primary isoflavones – genistein and daidzein. The body’s intestinal bacteria will metabolise a potent estrogenic compound called equol from the daidzein, and depending on how much equol is produced, will determine the health effect of soy on the body.


The biggest worries parents usually have regarding soy consumption for their children center primarily around isoflavones. These are a class of phytoestrogens, which are compounds that could act like estrogen in the body – the primary female sex hormone. For example, many authors or internet blog posts claim soy lowers serum testosterone levels in boys and increases breast cancer risk for girls.

The effects of isoflavones on estrogen receptors are apparently weak, meaning that soy intake may have minimal impact on hormononal levels in the human body. For example, in population studies, people who used to consume large amounts of soy products throughout life, have no apparent adverse effects. In fact, there’s a strong suggestion that soy intake protects against breast cancer later in life and, particularly, when consumed at an early age, such as the adolescent years. In the same way, research on humans haven’t shown that isoflavones have an impact on testosterone.

Another concern with soy is that much of the global production of soy is from genetically modified soy that is modified to resist high levels of pesticide residue such as glyphosate (ie. RoundUp). Also, GMO’s have not been tested on pregnant women and their unborn babies.


Other concerns raised are that soy components can affect the development of the reproductive organs or alter the reproductive system of children.

According to published data, there is no evidence so far that soy exerts any estrogenic effects on reproductive organs or alters reproductive development, volumes or structural characteristics. For example, a study published in the Journal of Nutrition in 2015, compared 50 boys and 51 girls who were breastfed or fed with cows-milk formula or soy formula, and researchers didn’t find any difference among those groups in regards to reproductive organ volumes and structural characteristics, from birth to five years of age.

When researchers evaluated other characteristics such as growth, weight, head circumference, they didn’t find any differences. However, breast-fed infants had a slight advantage on cognitive development compared with formula-fed babies, whether it was a cows milk formula or soy-based.

However, there is fairly extensive research on animals where female fertility is affected during pregnancy or neonatal

Photo credit: https://examine.com/nutrition/is-soy-good-or-bad/

exposure to isoflavones and life long exposure to phytoestrogens affected sperm production and animal litter sizes. Of note, different results occur between different animal species, which makes it difficult to generalize the conclusions and apply it to humans. This may be due to the large variability in the amount of isoflavones present in soybeans and soy products depending on how/where the soybean is grown, storage, how the product is processed and how isoflavones are metabolized in the body. For this reason, it is difficult to have an isoflavone database to show standard levels in all foods.

The European Food Safety Authority has recently stated that in post-menopausal women, isoflavones do not adversely affect the breast, thyroid or uterus. However, to date, soy consumption and thyroid status has not been directly investigated on humans. A reduced risk of developing breast cancer and reduced risk of dying from diagnosed breast cancer, has been found by consuming soy foods and isoflavones.

Men at risk of developing prostate cancer may reduce their risk by eating soy foods but not if they already have prostate cancer. Extremely high intakes of soy (approximately 360 mg of isoflavones per day) and over a long period (greater than 6-12 months), have shown adverse effects in some case studies of men, however, reasonable intakes have not been shown to affect testosterone levels, estrogen levels or fertility.

In Japan and China, average daily intake of isoflavones is reported to be 25-50 mg, while in Europe, consumption is estimated to be at approximately 1 mg per day.


Breastfeeding is the first and always the best choice for feeding newborns. However, there are some cases when infants can’t be fed with human milk, such as milk protein allergies. In these particular cases, soy-based formulas can be an alternative source of nutrition for babies who can’t tolerate cow’s milk proteins.

The limited human studies on healthy, full-term infants, suggests that soy-based formulas have no adverse health effects on growth, bone health and metabolic, reproductive, endocrine, immune and neurological function on soy fed infants compared to cow’s milk fed infants. However, given that infants consuming soy based formula’s, would be exposed to significantly higher levels of phytoestrogens than adults, there is a degree of caution to use soy based formula’s only if necessary, as in long term animal studies, sexual development may be affected. In cases of cow’s milk allergies, persistent lactose intolerance, galactosemia, gastrointestinal issues, religious considerations or vegetarian preference, the Nutrition Committees of the European Society of Pediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) and the American Academy of Pediatrics (AAP) indicate that soy based formula’s are acceptable to be used.

However, soy milk formula is not recommended for preterm infants due to the possible effects of phytoestrogens on growth and causing rickets, those who weighed less than 1800 grams at birth, and shouldn’t be used to help prevent colic or allergy.


As I’ve mentioned in previous blogs, a nutritious diet meeting the high demands during breastfeeding is extremely important, and soy happens to be one of the most protein-rich plant foods, thus helping lactating mothers to meet their macronutrient needs.

However, soy can indeed cause an allergic reaction in some babies who suffer from soy allergies, when passed into breast milk. If your child is experiencing a reaction to soy, talk to your child’s doctor to be referred to an Allergist, and speak to me on which formula is best for for your child.

Breastfeeding mothers who take soy can in fact increase breast milk concentrations of isoflavones, with apparently no adverse effects on their baby. However, in animal studies, there is evidence of soy isoflavones in pregnancy interfering with normal fertility, the development of the fetus’ reproductive organs and carrying pregnancies to term, which would then hold true for passing through to the infant during breastfeeding as well.

So, although, there is no strong human studies to prevent soy consumption during pregnancy and breastfeeding, given the sensitive period that the fetus and infant is developing reproductive organs, and the high nutrient demands of the mother’s body,  it may be advisable to include fermented and less processed soy products as part of a healthy diet while nursing, but perhaps more on an occasional basis until weaning occurs.


Based on these studies, I do believe that more large scale, long term human research is needed on the pubertal development and reproductive function of soy on infants, children and during pregnancy/breastfeeding. Unless it is necessary, I believe that soy formula should be minimized, particularly due to the large quantities of isoflavones that an infant will consume during a vulnerable growth period.

Moderate consumption of soy foods is unlikely to cause adverse issues in adults, and consuming a wide variety of plant-based proteins, including soy, will most likely have greater positive health impacts on cardiovascular health and reducing cancer risk. I do not believe that children and breastfeeding women need to avoid soy milk or soy products. Soy has its benefits, but like everything, moderation is key and by consuming a variety of nutritious whole foods, that are not processed and had soy proteins added in to them, you will ultimately reduce any negative effects that soy may or may not have. Organic, unprocessed and fermented soy (ie. miso, natto, soy sauce, tempeh), like other legumes, beans and plant-based foods, can be a part of a healthy diet for children.  With many nutrition and health choices, one must look at the benefit vs the risk and how our foods are grown, handled and processed, that can turn a healthy whole food into a food that can have a negative consequence.

It is important to understand critical health decisions related to humans are rarely made on one-off studies nor those that are based on animal studies alone. In adults, there are largely positive or at the least, neutral effects of eating soy products, however, in pregnancy, breastfeeding and infancy there are still some question marks that need further investigations. There is currently no recommendation on how much soy you should consume per day, however, remember that variety and moderation are key to healthy eating.

Again, if you are confused about the different types of studies mentioned or around on the internet, confused on if you should use soy infant formula for your child, or how you can ensure your vegetarian child is meeting their growing nutrient needs, or how to include soy in your diet while you are pregnant/breastfeeding, then please contact an Accredited Practicing Dietitian, focused on paediatrics and maternal health, like myself.



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