When your baby has food sensitivities, avoiding dairy and soy is often recommended because these are the most common food issues with food sensitive breast or bottle fed babies.
When avoiding soy, it is the soy protein that is causing the issues here. But soy in foods can take different forms, and can be found in the most surprising places.
Knowing about the different soy found in supermarket foods can help you make your own decision about the level of soy you avoid for your baby thorugh your breast milk.
Soy Protein in Foods
The foods that contain significant amounts of soy protein include all the well known soy foods:
soy milk
soy bean
tofu
tempeh
miso
soy sauce
edamame
textured soy protein foods (often found in mock or faux meat products if you are vegetarian).
These foods or foods containing these ingredients are to be avoided, and the food packaging will have a 'contains soy' allergen statment.
Let's look at the soy protein content of these foods (using an Australian food database):
FOOD OR DRINK | SOY PROTEIN CONTENT PER SERVE |
SOY MILK: 1 glass | 9.5 grams |
TOFU: 1 cup = 170g | 21 grams |
SOY FLOUR = 2/3 cup = 100g | 50 grams |
MISO PASTE, 1 TBSP = 12g | 1.5 grams |
SOY SAUCE: 1 TBSP = 21g | 1.5 grams |
SOY OIL: 1 TBSP = 18g | 0 grams |
We can see some very significant food sources of soy protein, which clearly needs to be
avoided due to the significant portien content of the food/ food ingredient.
The soy in some of these foods are processed with heat, and often fermented (for example soy sauce) which can cause partial hydrolysis, chemical modifications and use of proteolytic enzymes which may change the structural makeup of the soy bean protein and potentially render them potentially less allergenic.
At this point in time, the impacts of processing on the allergenicity of soybean protein have not been well studied.
Lets look at these different soy foods in more detail.
SOY FLOUR
Soy flour is very high in protein but the way we generally come across it in our foods is as a very small ingredients in breads and other bakery products.
The soy flour in these foods serve a technological function (improves the handling and machine-ability of the dough, as well as giving the bread better volume and crumb softness) and is not there to boost the protein cointent of the food.
Most foods such as bread contain very small amounts of soy flour, and when you read the ingredient list, it is obvious that the amount of soy flour is likely to be small as soy flour is listed towards the end of the ingredient list.
Despite this, the small amounts of soy such as soy flour are often best avoided if possible, as these small sources of soy do contain appreciable amounts of soy protein, and for most sensitive babies is often enough to cause issues.
SOY OIL
From the table above, you can see that soy oil does not contain any protein when tested (Australian database).
According to a clinical research paper in 2021 (Taylor et al.);
"Ingredients with low protein content likely pose little risk to soy-allergic individuals especially when used in small percentages in formulated food products. However, only highly refined soy oil has been clinically demonstrated as unable to provoke reactions in soy-allergic individuals (Bush et al., 1985). The allergenicity of other soy ingredients with low protein content such as soy lecithin and soy fiber remains to be demonstrated."
This means that soy oil is liklely well tolerated even when foods are eaten directly by an individual with soy allergy. When one takes into account the diluting effects of breast milk, technically soy oil should not be an issue.
An exception is cold pressed soy oil which is best excluded. Cold-pressed soy bean oil has a protein profile similar to soybean flour, but is not typically used as an ingredient in foods. .
SOY LECITHIN
Soy lecithin is made from the fat components of the soy bean. The protein is mostly removed during the purification process.
Consequently, soy lecithin potentially contain trace (very small) levels of soy proteins and these have been found to include soy allergens.
Research indicates that most individuals allergic to soy can safely eat soy lecithin directly.
However, the 2021 review (Taylor et al.) concludes that other soy ingredients with low protein content such as soy lecithin, the potential impact on Ige allergic individuals (direct ingestion) needs to be properly demonstrated before it can be confidently recommended to be safe to be eaten directly by persons with a soy allergy.
Generally, breast feeding mothers removing dairy and soy from their diet are likly to find that soy lecithin will be tolerated by their breast feeding babies with soy protein issues, however as per information above, there may be times when a soy lecithin could potentially present an issue so is ften generally avoided.
UNITED STATES PERSPECTIVE (does not apply to Australia): highly refined soybean oil and certain uses of soy lecithin are exempt from source labelling.
SOY FIBRE
Soy fibre may have differing amounts of protein deepening on its extraction process, and best viewed as a 'to be excluded' soy containing soy protein.
Australian perspective: soy fibre is less commonly seen in Austrlain food products, which is different to the Amercan food manufacture where soy is more commonly used. Still recommend be excluded if you come across it!
SOY DERIVED FOOD INGREDIENTS
The next level down in terms of imperceptible amounts of soy protein are food or processing components derived from soy.
Foods that are made from soy but are so far removed from soy that they are not considered to be a soy continuing food are not considered to be be an issue in this space. This means foods derived from soy but do not need to be declared through an allergen statement.
Usually if soy (and dairy) is being fastidiously excluded from the diet for a breast-fed baby, ongoing issues (if food related) more likely to another food sensitivity/allergen.
MAY CONTAIN SOY
Australian perspective: as this is a voluntary code, the use of this claim gives no insight what so ever if this claim is made is to the actual risk of any soy protein cross contamination.
Refer to the 'May Contain' blog if you want to kbnow more about this.
THE SOY WRAP
This information can be used as a guide so you can make your own personal choice about which foods to exclude or not when pursuing a soy free diet for your breast fed baby with soy allergy or intolerance.
My personal interest is sharing evidence based information, with the Australian perspective - especially as this area can be fraught with lots of different information sharing and opinions.
Frances Walker
Dietitian specialising in Food intolerances in breast fed babies
UPDATED FEBUARY 2025
REFERENCES
Steve L. Taylor, Geert F. Houben, W.Marty Blom, Joost Westerhout, Benjamin C. Remington, Rene W.R. Crevel, Simon Brooke-Taylor, Joe L. Baumert,
The population threshold for soy as an allergenic food – Why did the Reference Dose decrease in VITAL 3.0?,Trends in Food Science & Technology, Volume 112, 2021, Pages 99-108, ISSN 0924-2244,
Australian Food Composition data base: https://www.foodstandards.gov.au/science-data/monitoringnutrients/afcd
ASCIA SUMMARY SOY ALLERGY: https://www.allergy.org.au/patients/food-allergy/ascia-dietary-avoidance-for-food-allergy/soy