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Onions & Digestion

author image Jessica Jacobs
Jessica Jacobs is a registered dietitian and professional writer, contributing to "Fitness Magazine" since 2003. She received a B.A. in journalism from Arizona State University and an M.S. in nutrition and food sciences from the University of Texas at Austin.

Onions are vegetables with a distinctive taste, commonly used in recipes. Additionally, onions have several uses in herbal medicine. However, some individuals have difficulty digesting onions. These digestive problems can result from either an allergy or an intolerance to onions.


Onions are a member of the allium group of vegetables, which also includes garlic, scallions, green onions, spring onions, shallots and chives. Onions contain odoriferous sulfur compounds including thiosulfinates, sulfoxides and sulfides. Additionally, onions can help your body grow healthy bifido bacteria that reduce the growth of harmful bacteria. Cysteine sulfoxide is the compound in onions responsible for the flavor of the onion. Cysteine sulfoxide also causes your eyes to tear when you cut onions. These compounds have several medicinal properties.


Inlulin is a fiber present in onions. Inulin is a beneficial food source for the healthy bacteria in your intestines. Consuming inlulin allows your body to maintain healthy levels of good bacteria. The presence of good bacteria promotes regular bowel movements. The thiosulfinates in onions also have antibacterial properties that can cause harm to these same beneficial bacteria. Individuals sensitive to these antibacterial properties might have difficulty digesting foods after they eat onions, especially raw onions.

Allergy and Intolerance

You can have either an internal or external allergy to onions. A topical allergy to onions results in contact dermatitis. On the other hand, an internal allergy results from the consumption of onions. Symptoms of an internal allergy include bloating, gas, diarrhea and nausea. If you exhibit these symptoms, you can have either an allergy or an intolerance to onions. If you have an intolerance to onions, you can alleviate the symptoms by eliminating onions from your diet. Anti-histamines and topical steroids can help to treat allergies to onions.


According to the book “Encyclopedia of Natural Medicine,” the anti-bacterial properties of onions’ thiosulfinates can help to fight harmful bacteria, including Bacillus subtilis, salmonella and E. coli. Other compounds in onions can help to lower your blood pressure, prevent blood clotting, induce perspiration and function as a decongestant. Onions also have antiallergenic, antimicrobial and anti-asthmatic properties.

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