Natto is a Japanese traditional food made from fermented soybeans. We report a case of
anaphylaxis caused by natto and review the literature. The patient was a 22-year-old man who showed systemic eruption with
itching and pectoralgia about 10 hours after eating a meal containing natto. Results of skin tests for soybean
allergen were negative, and the
allergen remained unidentified. We then used a food elimination trial to confirm the
allergy. However the patient did not refrain from eating natto, and he had three
anaphylactic reactions might have been caused by natto. Each event occurred 10 to 14 hours after he ate a meal containing natto. We performed detailed examinations to determine the
allergen. First, the prick-by-prick tests with natto and its characteristic viscous yarn-like surface were done and yielded positive results. Next, a provocation test with commercial natto (50 g) was performed and caused systemic eruption and pectoralgia about 9 hours after ingestion of the natto. The patients'plasma
histamine level was elevated during the anaphylactic event.
Anaphylaxis caused by natto was diagnosed. Recent studies have shown that the
anaphylaxis caused by natto is of late-onset. Late-onset
anaphylaxis can be considered one of
IgE-mediated
allergic reactions. The viscous surface of natto contains
poly-gamma-glutamic acid (
PGA). The hypothesized mechanism of late-onset
anaphylaxis is delayed absorption or release of
PGA into the bowel. In our case, the patient ate heated natto, we therefore speculate that suspect
allergens were heat resistant. Patients with natto
allergy must not eat natto, whether or not it is cooked or heated. Natto may induce
allergic reactions up to a half-day after ingestion; thus, the
clinical course and patient's diet must be considered during medical examination. Natto has recently gained popularity as a health food in foreign countries. The existence or natto
allergy should be more widely recognized.