Soy Protein Intolerance Clinical Presentation

Updated: Oct 06, 2017
  • Author: Stefano Guandalini, MD, AGAF; Chief Editor: Carmen Cuffari, MD  more...
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The typical presentation is that of an infant who develops atopic dermatitis or cow's milk protein intolerance, which resolves with substitution of a soy-based formula but recurs 1 or 2 weeks later. Parents may report a recrudescence of dermatitis or GI symptoms. Usually, the infant presents with watery diarrhea and vomiting.

Soy protein intolerance may cause different clinical syndromes, both immunoglobulin E (IgE)-mediated and non–IgE-mediated, ranging from skin, GI, or respiratory tract reactions up to anaphylaxis. These reactions include the following:

  • Atopic dermatitis

  • Food protein–induced enterocolitis syndrome (FPIES)

  • Intestinal villous atrophy (malabsorption syndrome)

  • Eosinophilic gastroenteritis

  • Allergic proctocolitis

  • Constipation

  • Anaphylaxis (rare)

A European multicenter study, which included both children and adults (mean age, 26.4 y; range 1-69 y), showed that bronchial asthma and seasonal rhinoconjunctivitis are the most frequent symptoms (65% of patients), followed by atopic dermatitis (33%). In this group of patients, the first reaction to soy occurred at a mean age of 19 (±10) years (range, 3-44 y). [17]

In young children and in infants, soy protein intolerance occurs mainly with dermatological and GI manifestations. Some children present with atopic dermatitis as a major symptom; however, most patients present with profuse vomiting and watery diarrhea.

Soy proteins can cause GI manifestations similar to those described in the Medscape Reference article Protein Intolerance. Although the prevalence of soy protein allergy has been traditionally considered to be quite high (for cross-reactivity) in infants and children with milk protein allergy presenting with FPIES, a large epidemiological investigation failed to confirm such high prevalence. [18]

GI symptoms are very frequent in children with cow’s milk proctocolitis or enterocolitis who are fed with soy proteins. Symptoms usually begin within 2 weeks of the infant's first feeding with soy-derived milk. Sometimes mucus can be present in the stools, but blood is rarely noted. Even if frank manifestations of colitis are absent, inflammatory changes in the colonic mucosa are frequently encountered.

Small-bowel atrophy has been documented in different studies. The degree of villous atrophy may be similar to that found in celiac disease. The mucosal damage may lead to malabsorption, hypoalbuminemia, and failure to thrive.

Some breast-fed infants can present with red blood mixed in stools as a result of soy allergic proctocolitis. These infants usually appear healthy, and hematochezia is the only symptom. In some cases, the syndrome, which can be traced down to maternally ingested soy in about 30% of cases, does not respond to withdrawal of food allergens from the maternal diet. [19]

A case of recurrent intussusception in an infant with a patch test positive to soy has been reported. The intussusceptions, which were considered a consequence of lymphoid hyperplasia, resolved with die and recurred after reintroduction of soy. [20]

Food allergies (including to soy protein) may lead to constipation. Removal of the allergen from the diet is typically very effective. [21]

The possibility of anaphylaxis occurring in adults ingesting generic drugs containing soybean oil has also been reported. [22]

In children, approximately 50% of those with soy allergy can outgrow their allergy by age 7 years. Absolute soy IgE levels were useful predictors of outgrowing soy allergy. [23]



The physical examination findings depend on the clinical picture and the duration of symptoms.

  • The most frequent presentation is enterocolitis syndrome; therefore, the infant appears dehydrated, with weight loss and sunken eyes.

  • In case of proctocolitis, the infant usually appears healthy and has normal weight gain.

  • In the less frequent case of soy-induced enteropathy, the infant has a low weight-to-length ratio and usually presents with dystrophia.

  • The signs and symptoms are related to the degree of the malnutrition. For example, edema is related to hypoalbuminemia, dermatitis enteropathica is related to low zinc level, and rickets is related to vitamin D deficiency.



According to some studies in animal models, soy proteins appear to be less sensitizing than cow's milk proteins. However, because a 30-kD protein in soy may induce cross-reactivity to cow’s milk caseins, infants with a previous history of cow's milk protein intolerance have a greater risk of developing soy protein intolerance.

The intestinal mucosa damaged by cow's milk proteins may allow increased uptake of the potentially allergenic soy proteins.