Soy beans are broken down into powder, oils and additives that add protein and flavor to commercially prepared foods. Soy is one of the eight most common food allergens in the United States, according to the University of Maryland. Soy intolerance differs from soy allergy. A true soy allergy involves the immune system recognizing soy protein as a foreign substance and trying to fight it. Soy intolerance does not involve the immune system. Instead, the body may have trouble digesting soy or find it irritating to the digestive system, resulting in uncomfortable symptoms.
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Soy protein may irritate your gastrointestinal tract if you are soy intolerant. You may develop abdominal cramping or pain and diarrhea. Intestinal gas and abdominal bloating, vomiting and nausea, the sensation of needing to vomit, may also occur. Gastrointestinal symptoms may happen immediately after ingesting soy protein or hours later, according to Cleveland Clinic. You may also develop heartburn from soy intolerance. Heartburn causes a burning sensation beneath the breastbone or in the throat. Babies intolerant of soy may experience reflux, or spitting up, of soy formula or foods containing soy. A baby may indicate abdominal pain or discomfort after having soy by pulling legs to chest, flailing arms and crying.
Intolerance to soy protein may occur immediately or occur several days after ingestion. You may experience changes in mood or behavior after consuming soy protein if you are intolerant. Symptoms may include irritability or nervousness or depressed mood, according to a 2007 article in "Living Without Magazine." Infants intolerant of soy may exhibit fussiness, irritability or discomfort.
Soy intolerance may cause headaches in susceptible people. Headaches may be mild and occur soon after eating soy. Headaches accompanied by severe pain, sensitivity to light and sound and nausea or vomiting, known as a migraine, may also occur with soy intolerance.
Symptoms of soy intolerance and a true allergy to soy may overlap. Meet with your physician for allergy testing if needed to help determine whether you have soy allergy or intolerance. Emergency symptoms include trouble breathing, swelling of the lips, face or throat, tingling in the throat, itchy skin rash or unconsciousness. Emergency symptoms may occur even if you’ve only had a mild reaction to soy in the past.