Soybeans are a good source of protein, and soy-based products like soy milk and tofu are loved by many. But for some, soy can lead to unpleasant symptoms — indeed, products like soy milk do have the potential to make you poop and experience other digestive issues.
Here are the common reasons why soy can cause loose stools, stomach pain, gas, bloating and other symptoms.
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1. You're Allergic to Soy
If soy or related products like soy sauce give you an upset stomach or diarrhea, a soy allergy may be to blame.
Soybeans, soy milk and many soy-derived products contain soy protein allergens, according to the University of Rochester Medical Center. Common allergy-inducing products include:
- Soy cheese and yogurt
- Soy sauce
- Soy flour
- Soy protein isolate
And if you're allergic, eating products like soy milk, soy sauce, soybean oil, edamame, miso soup or tofu can cause diarrhea and other symptoms, including:
- Stomach cramps
- Nausea and vomiting
- Tightness in your throat
- Difficulty breathing
Fix it: If soy milk and tofu do make you poop on the regular, visit your doctor to test for a soy allergy, per the Cleveland Clinic. If you are indeed allergic, avoid soy and soy-based products so you don't have another reaction. Some hidden sources of soy to keep an eye out for include:
- Vegetable broth
- Vegetable starch
- Vegetable gum
- Hydrolyzed vegetable protein
- "Natural" flavorings
Your doctor may also prescribe you medication — like an EpiPen — to use in the event of an allergic reaction.
Some people can have an extreme allergic reaction called anaphylaxis, where your throat closes up and makes it difficult to breathe, per the Mayo Clinic. Seek medical care immediately if this happens to you.
2. You Have a Soy Intolerance
If soy regularly makes your belly ache, an allergy isn't the only potential culprit. A soy intolerance could be the cause of your bloating, gas or other symptoms.
- Stomach pain
- Upset stomach
Soy intolerance diarrhea and other digestive issues usually develop within a few hours of eating the offending food, per the Cleveland Clinic. And when it comes to how long soy intolerance symptoms last, that varies by the person. In general, though, reactions can last as long as a few days, depending on how long it takes you to digest.
Fix it: Unlike allergies, there are no blood or skin tests to detect a soy intolerance, per the Cleveland Clinic. The offending substance is found by eliminating foods from your diet to narrow down the list of suspects until the culprit is identified, often by trial and error. So if you feel like you have a tofu intolerance, keeping a food diary can help you track any symptoms you experience when you eat soy-based foods.
If you do seem to have a soy protein intolerance or sudden soy intolerance, the best way to avoid soy stomach cramps and other symptoms is to skip soy products altogether, according to the Cleveland Clinic.
Soy Intolerance vs. Allergy
Soy and soy products like tofu can upset your stomach for a variety of reasons. Luckily, your symptoms can help you determine if you have an intolerance or an allergy.
If it's an intolerance, you'll primarily experience digestive problems, per the Cleveland Clinic. On the other hand, if you're allergic to soy, you'll also experience non-digestive issues like itching or shortness of breath.
3. Soy Contains Oligosaccharides
Products like soy milk can cause diarrhea in adults and children alike. And if you don't have an allergy or intolerance but soy milk does still make you poop, a component of soy could be the cause of your digestive distress.
Oligosaccharides are a type of naturally occurring carbohydrate, and they make up much of the carbohydrates in soybeans, according to December 2016 research in Nutrients. This plant-based carb can be difficult to digest for some people, which can lead to symptoms like gas, bloating, diarrhea and abdominal pain, per a July 2012 study in Therapeutic Advances in Gastroenterology.
In other words, soybeans do cause gas for some. So if you've noticed tofu makes you gassy or gives you a stomach ache, oligosaccharides may be the reason why.
Fix it: If you regularly have an upset stomach after eating tofu, soy sauce or other soy products, keeping a food diary can help you determine if you also have a reaction to other oligosaccharide-rich foods like dairy products or table sugar.
If you notice a pattern, following a low-FODMAP diet — with an emphasis on avoiding foods high in oligosaccharides — may help you reduce your symptoms, per the Therapeutic Advances in Gastroenterology research.
Is Tofu Good for an Upset Stomach?
For people who aren't sensitive to soy products, tofu can be a protein-rich addition to a bland diet, which is made up of easily digestible foods in the event of a gastrointestinal illness or problem.
- Cleveland Clinic: "Soy Allergy"
- Mayo Clinic: "Food allergy"
- Cleveland Clinic: "Food intolerance"
- University of Rochester Medical Center: "Soy Allergy Diet"
- Therapeutic Advances in Gastroenterology: "Fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) and nonallergic food intolerance: FODMAPs or food chemicals?"
- Nutrients: "Soy and Health Update: Evaluation of the Clinical and Epidemiologic Literature"
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.