Soy beans are legumes and thus related to peas, lupin, beans, lenses, chickpeas and peanuts. They all belong to the same botanical family, the Leguminoseae/ Fabaceae. Among those allergic to one legume it is not unusual to react to several legumes due to structural relations between proteins. Allergy to peanuts is sometimes accompanied with allergy to soy, pea, beans, lenses or lupin.
Soy beans are raw material for the production of flour, protein, oil and lecithin. Different procedures for protein isolation lead to soy isolate soy concentrate and soy texturate. Soy lecithin (E322), another product from soy beans, is used as emulsifier between fat and water. Soy lecithin is not allergic but contains traces of soy protein from the production process. These tiny amounts of protein might possibly cause a problem for the most sensitive soy individuals.
Oil from soy produced through evaporation have not been shown to contain protein residues and is thus not regarded as a risk for soy allergic individuals.
In addition to its nutritional values, soy proteins have also excellent technological properties. Soy protein can be used as an ingredient in different type of food products and as vegetarian alternatives to meat products (vegetarian sausage, pastry, hamburgers). Ice cream and milk substitute can be produced from soy beans.
Several different proteins present in the soy bean have been identified as responsible for allergic reactions.
Labeling
The presence of soybeans and product thereof must always be declared, see further in LIVSFS 2004:27 Livsmedelsverkets föreskrifter om märkning och presentation av livsmedel [in Swedish] (see link to the right).
Examples of methods of analysis
Commercial test kits are available for soy protein quantification. The limit of quantification is between 1 to 10 mg/kg (ppm).
Soy can be identified with DNA methods. A positive result in a DNA analysis indicates the presence of soy in a sample.
Providers of test kit often have a validation protocol to be submitted with the test kit upon request. Laboratories using commercial assays must establish in house control of limit of detection and limit of quantification in actual matrices even if the test has been validated by the provider.
Allergic reactions/Doses
The lowest dose of soy protein that elicitates an allergic reaction is not known. The concentrations of soy protein that have been detected in food products causing allergic reactions are listed below.
Food |
Year |
Consumed amount |
Soy protein conc.
mg/kg |
Estimated dose |
Reported reaction |
Sex/Age |
| Sausage |
1994 |
25 g |
500 |
12.5 mg |
Anaphylactic reaction*, breathing difficulties |
m/5 years |
| Rice noodles |
1996 |
100 g |
2 000 |
200 mg |
Stomach pain |
f/25 years |
| Sausage |
1997 |
50 g |
4 500 |
225 mg |
Breathing difficulties, swelling of lips |
m/11 years |
| Hamburger |
1992 |
25 g |
21 000 |
525 mg |
Fatal anaphylaxis** |
f/9 years |
| Meat balls |
1995 |
50 g |
30 000 |
1500 mg |
Fatal anaphylaxis |
m/17 years |
| Hamburger |
2003 |
50 g |
57 500 |
2875 mg |
Anaphylactic reaction |
m/8 years |
| Kebab |
1994 |
50 g |
70 000 |
3500 mg |
Fatal anaphylaxis |
m/9 years |
| Schnitzel |
2008 |
ca 100 g |
24 |
2.4 mg |
Asthma, urticaria |
m/13 years |
* Anaphylactic reaction means that the allergic individual suffers from blood pressure drop, respiratory comprise/cramps in the airways and a systemic reaction, called anaphylactic shock
** Fatal anaphylaxis means that the shock develops to unconsciousness and death.
Provocation studies in soy allergic individuals (age range from 1 to 69 years) showed subjective symptoms at doses of 10 mg of soy, corresponding to 5.3 mg soy protein and objective symptoms at soy protein concentrations of 241 mg (Ballmer-Weber et al., 2007).