Why Walnuts Might Upset Your Stomach

Walnuts are often hailed as a nutritional powerhouse and with good reason. Rich in omega-3 fatty acids, fiber, plant-based protein, and antioxidants, they support heart health, brain function, and even longevity. But for some, these little nuts pack more than just nutrients: They can also bring on unexpected stomach trouble.

If walnuts leave you bloated, crampy, or running to the bathroom, you’re not alone. Below are five common reasons walnuts might upset your stomach and simple ways to fix it so you can still enjoy their benefits without the bellyache.

1. You’re Eating Too Many at Once

A standard serving of walnuts is about 1 ounce, or a small handful (roughly 14 halves). But because they’re delicious and easy to snack on, it’s easy to go overboard.

Walnuts are high in fat and fiber two nutrients that slow digestion. In excess, they can overwhelm the digestive system, especially if you're not used to a high-fiber diet.

Fix it: Start with a smaller serving and drink water while eating them. Slowly increase your intake over time to give your digestive system a chance to adjust.

2. They’re Triggering Your IBS Symptoms

If you live with irritable bowel syndrome (IBS), you may already know that high-fiber or high-fat foods can be triggers. Even though walnuts are packed with healthy fats, their fiber and fat content may stimulate IBS symptoms like bloating, gas, or cramping in some people.

Fix it: Stick with smaller portions and monitor your response. You may tolerate walnuts better when combined with other foods like in a salad or yogurt bowl rather than eating them alone.

3. You May Have a Tree Nut Allergy

Tree nut allergies are one of the top eight food allergens in the U.S., and reactions can range from mild to severe. While hives and swelling are common symptoms, digestive issues like stomach cramps, nausea, vomiting, or diarrhea can also be signs of a food allergy.

Fix it: If you suspect an allergy, see an allergist for testing. Avoid walnuts and other tree nuts until you have a clear diagnosis.

4. You Might Have a Food Intolerance

Unlike allergies, food intolerances don't involve the immune system, but they can still make you feel miserable. If your body struggles to digest components in walnuts whether it's the fat, fiber, or another compound you could experience symptoms like gas, bloating, and indigestion.

Fix it: Consider keeping a food diary to track symptoms. If walnuts consistently cause issues and allergy has been ruled out, a food intolerance may be to blame.

5. You Have Diverticulitis

Diverticulitis occurs when small pouches (diverticula) in the colon become inflamed or infected. While nuts like walnuts don’t cause the condition, they can exacerbate symptoms during a flare-up.

Fix it: If you’re in the midst of a diverticulitis episode, stick to a low-fiber, liquid diet until your symptoms subside. Once you’re feeling better, walnuts can generally be safely reintroduced.

What About Tannins and Phytates?

Walnuts contain naturally occurring compounds called tannins and phytates, sometimes referred to as "anti-nutrients." These may slightly reduce nutrient absorption but have not been shown to cause digestive discomfort in humans.

In fact, studies show that these compounds may have health benefits of their own, including antioxidant and anti-inflammatory effects. So unless you have a specific sensitivity, there’s no need to worry about them disrupting your digestion.

How to Enjoy Walnuts Without the Stomachache

If you’ve had tummy troubles after eating walnuts but don’t want to give them up, here are a few simple tips to try:

• Stick to the right portion size. One ounce (about a handful) is ideal for most people.

• Drink water with walnuts. This helps the fiber move smoothly through your system.

• Balance your fiber intake. A healthy target is 25–35 grams of fiber per day, but going well over 40 grams may cause digestive distress.

• Don’t eat them on an empty stomach. Pairing walnuts with other foods like fruit, yogurt, or oatmeal can ease digestion.

• Talk to your doctor. If walnuts repeatedly cause discomfort, speak with a healthcare provider to rule out allergies or gastrointestinal conditions.

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