3 Known Side Effects Of Eating Too Many Walnuts

Side Effects Of Eating Walnuts

Walnuts are universally considered a health food, packed as they are with healthy fats, fiber, antioxidants, and protein. They have many benefits for your overall health, skin, and hair. And they’re tasty to boot. From granola to baked goods, walnuts can be a real treat. You can even use them to add a crunch to your salads! But like most foods, overeating them isn’t the best idea.

The standard serving size for walnuts is 1 oz or 28 g. That’s about 14 halves. Having a few more than this won’t probably give you side effects. But having a cupful, say, every day for a long time may not be the healthiest choice. Plus, your existing conditions and diet might make it worse. So before you reach for another scoop, learn about these 3 side effects of walnuts. These side effects are linked to English walnuts (has a large seed and a thinner shell), one of the most common types, and Indian walnuts.


1. Stomach Problems

Walnuts can stress out your digestive tract

Fiber is great for keeping your digestive system healthy and well. You can get a small amount – about 2 grams – in a handful of walnuts. This is just a fraction of the recommended daily intake of 21 to 38 grams, so it probably won’t cause issues. But if you already have a high-fiber diet, walnuts may work against you.


Consuming lots of fiber in a short time can stress out your digestive tract. If the intestinal bacteria isn’t used to it, you’ll end up with gas, diarrhea, and bloating. You might even have stomach cramps. To avert these side effects, avoid overeating walnuts if you already have had foods rich in fiber.

This includes whole fruits, raw veggies, whole wheat bread, brown rice, and legumes. You might also be taking a fiber supplement or munching on snacks with added fiber. If so, enjoy walnuts in moderation.


2. Weight Gain

Walnuts can cause weight gain

Like other nuts, walnuts are energy-dense. One cup has 765 calories! But thanks to the healthy fats and fiber, these nuts can also increase satiety levels. This means that you’ll be less likely to overeat later on, helping you lose weight. But if you still end up overeating? Walnuts will actually contribute to weight gain.


The key is to stop eating when you’re full. If you snack on walnuts but force yourself to eat an entire meal – even if you’re not hungry anymore – you’ll just pack on the calories. This is especially true if you eat walnuts and energy-dense, nutrient poor foods.

The solution? Always keep your overall caloric intake in check. Adult women should aim for 1,600 to 2,400 calories each day, while adult men should aim for 2,000 to 3,000 calories. More active individuals will be on the higher end of these ranges.1 When part of a healthy, controlled energy intake, walnuts will not cause significant weight gain.2


3. Allergic Reaction

Symptoms of an allergic reaction to walnuts will vary

If you are allergic to walnuts, eating even a few can set off a reaction. When it comes to common food allergens, tree nuts take first place. This includes walnuts, so it’s crucial to be careful. Keep in mind that if you’re allergic to other tree nuts – like almonds or pistachios – there’s a good chance that you’re also allergic to walnuts.3 And if you’re not sure, see an allergist.


Symptoms of an allergic reaction to walnuts will vary. Hives, redness, and itchiness are common. You may also feel nauseous or vomit. Diarrhea, abdominal pain, sneezing, dry coughing, and nasal congestion are likely. If you experience these side effects, take an antihistamine immediately.

More severe side effects include shortness of breath and trouble swallowing. The throat and mouth might also swell up so much that it’s hard to breathe. Chest pain, weak pulse, and a drop in blood pressure are all causes of concern. These symptoms are life-threatening and call for immediate medical attention.4


If you’re prone to allergic reactions, be cautious with walnuts. They’re often added to dishes like salads and pasta. After all, the only way to avoid these side effects of walnuts is to avoid them.

Side Effects Of Black Walnuts

The Black walnut is a different story. Its active compound, juglone, is a natural toxin. This can damage DNA and human fibroblasts, the cells that make collagen. However, juglone is primarily found in the root and hull of black walnut, stressing the importance of proper preparation.5

Consuming excess black walnut may cause diarrhea or loose stools.6 Also, having black walnut while pregnant could theoretically cause birth defects or negatively impact the growth of the fetus or potentially induce a miscarriage.7 Otherwise, black walnuts are safe to consume in moderation just like other types.

Side Effects Of Green Walnuts

A green walnut is an immature walnut that is harvested early and, thus, is green. The color starts to darken immediately when picked from trees. Green walnut is in demand for spirit confections like nocino and vin de noix. It is also used to make an old traditional marmalade, a pickle, to flavor vodkas, and for home remedies.

Caution: Green walnut is not for direct consumption. It is only for infusing its flavor and other properties into liqueur and tinctures.

In moderation, walnuts are definitely a part of a healthy diet. They’re full of amazing nutrients, so don’t ignore them! Keep your meals diverse for the best results.