5 Reasons Walnuts Might Upset Your Stomach and How to Get Relief

Walnuts deserve a spot near the top of the list of "Foods You Should Eat More Often." The rich, crunchy tree nuts provide fiber, omega-3 fatty acids, and even brain-boosting antioxidants. So if eating them gives you a stomachache, you might be wondering what the problem is.

Walnuts aren't necessarily known for causing belly pain, but some people have had gastrointestinal (GI) symptoms after snacking on them.

Here are five possible reasons why eating walnuts might lead to GI issues and what you can do to feel better.

1. You Ate Too Many

Eating too much of any food can give you a bellyache. But foods that are high in fiber and fat — including walnuts — can make you particularly uncomfortable when you scarf down a lot at once, especially if you're not used to eating a lot of roughage.

"You can get abdominal cramping, bloating, or gas because of the fiber or fat content," says Supriya Rao, MD, a board-certified gastroenterologist with Integrated Gastroenterology Consultants in Lowell, Massachusetts.

2. They're Triggering Your Irritable Bowel Syndrome

You might be more likely to experience these symptoms intensely if you have IBS. "In people with IBS, the nerve endings in the gut are hypersensitive," Rao says. "So if you're going to have bloating from walnuts, that may make someone with IBS feel worse."

3. You Have a Tree Nut Allergy

4. You Have a Food Intolerance

A food intolerance happens when your body has trouble digesting a specific food. Unlike a food allergy, a food intolerance doesn't have the potential to trigger life-threatening symptoms. But it can make you uncomfortable and cause digestive problems like cramping, nausea, diarrhea, gas, and heartburn. It also can cause headaches.

But if walnuts just don't seem to agree with you — and you and your doctor have ruled out other causes — an intolerance could be the culprit.

5. You Have Diverticulitis

Diverticulitis occurs when small, bulging pouches called diverticula, which can form in the digestive tract with age, develop temporary inflammation or infection.

Eating walnuts or other nuts and seeds doesn't cause the pouches to form, and if you already have diverticula, it's fine to continue eating these foods, Rao says.

But if diverticulitis develops and causes symptoms such as fever or nausea, you'll want to steer clear of eating nuts and seeds until you feel better. "When you have an active infection, you should stick to a liquid diet until it passes," Rao says.

What About Antinutrients?

Still, antinutrients probably can't directly cause you digestive pain. They aren't toxic to humans, and research hasn't shown that they can cause stomach problems. "There's not great evidence behind those claims," Rao says.

What to Do When Walnuts Cause Stomach Pain

If you want to eat more walnuts but your stomach doesn't agree, these tips can help ward off symptoms:

• ‌Pay attention to your portion.‌ A serving size of walnuts is 1 ounce (oz).

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   This is about a handful if you’re measuring up in a hurry.

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   Try a smaller helping if you regularly grab more than a serving of walnuts and get an upset stomach.
• ‌Pair water with walnuts.‌ Drinking more water when you increase your intake of high-fiber foods like walnuts can help the fiber move through your GI tract more efficiently.

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   If the walnuts upset your stomach, try drinking a glass of water whenever you eat them. This may help reduce symptoms like bloating and gas, Rao says.
• ‌Pay attention to your overall fiber intake.‌ A 1-oz serving of walnuts contains 1.47 grams (g) of fiber. Consider how that amount fits into your diet, and find ways to lower your intake if it seems like you're overdoing it.

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• ‌Talk with your doctor.‌ Let your primary care provider know if walnuts give you a stomachache more than once or twice, Rao says. Together, you can discuss your symptoms and determine whether you should see a gastroenterologist or an allergist.

The Takeaway

• Eating too many walnuts can cause stomach discomfort due to their fiber and fat content.
• Some people with an underlying health condition, such as irritable bowel syndrome (IBS) or diverticulitis, experience stomach symptoms after eating walnuts.
• If you have a walnut allergy or intolerance, it can cause stomach pain, gas, and bloating. You may also experience nausea or diarrhea.
• Depending on why eating walnuts causes you to have GI distress, you may not have to miss out on their health benefits. Add walnuts to your diet slowly. Drink plenty of water while eating them. And talk with your doctor about any persistent stomach symptoms that may indicate an underlying health issue.