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What are Nightshades and Do They Cause Inflammation?

How to know if you’re sensitive to nightshades

By
Monica Reinagel, MS, LD/N, CNS
September 13, 2011
Episode #154

Ray recently asked me to weigh in on conflicting information he’s read about tomatoes, peppers, and other foods in the “nightshade” family:

“Many folks say that nightshades cause inflammation and should be avoided,” he writes, “but you recommend them as anti-inflammatory in your book, [The Inflammation-Free Diet Plan]. Can you clarify?”

The same week, I got an email from Jim, who wrote,

“I have been avoiding all nightshades for about 5 months now in an effort to clear up [an inflammatory condition] but I haven't really seen an improvement. I would love to return to eating green chiles and tomatoes.”

Let me see if I can clear up some of the confusion about nightshades and inflammation.

Spoiler Alert: Good news for you, Jim!

What Are Nightshades?

Tomatoes, peppers, potatoes, and eggplant (as well as tobacco) all belong to the same botanical family, commonly known as the nightshades. The Latin name for this family of plants is Solanaceae, because all of them produce an alkaloid compound called solanine. Solanine is part of these plants’ natural defense system, acting as a nerve poison on insects that try to eat the plants. 

Is Solanine Toxic to Humans?

Obviously, it’s going to take a lot more solanine to cause problems for a human being than for a bug. And for most people, the amount of solanine you’d ingest by eating even large quantities of tomatoes and peppers isn't enough to cause any problems.

By the way – Solanine is concentrated in the leaves and stems, and that’s one of the reasons we don’t eat those parts of the plants. A big salad of tomato or potato leaves might actually contain enough solanine to give you an upset stomach. (And just in case you’re wondering, sweet potatoes are not in the nightshade family and that’s why we can enjoy sweet potato greens.)

Perhaps you’ve also heard that potatoes with sprouting eyes are poisonous. That’s because potatoes that have started to sprout or have developed a greenish tint to their skins are often higher in solanine.  It’s best not to eat them.

Do Nightshades Cause Joint Pain?

Because nightshades are only a problem for a small number of people, it’s overkill to suggest that everyone should avoid them.

People with arthritis are sometimes advised to avoid all nightshade plants because they are said to cause inflammation.  But this advice really only applies to people who have a sensitivity to solanine.  For these folks, eating nightshade plants causes an inflammatory reaction—including joint pain. 

Because most people are not sensitive to solanine, however, I think it’s  misleading to characterize nightshade plants as “inflammatory,” and it’s certainly overkill to suggest that everyone with arthritis should avoid them—especially because they have so much going for them nutritionally.

Nightshade plants are high in antioxidants, which actually help reduce inflammation.  And chili peppers also contain capsaicin, a strongly anti-inflammatory compound. So, if you’re an arthritis sufferer, I’d think these would be foods you’d want to eat more of—unless, of course, you are among the minority that is sensitive to them.

See also: Foods that Fight Inflammation

How to Tell if You’re Sensitive to Nightshades

If you have joint pain—and tomatoes, peppers, potatoes, and/or eggplant are a regular part of your diet—try eliminating all nightshades from your diet for at least two weeks and see if you notice any difference in your symptoms. If you see an improvement, you might be among those who are sensitive to solanine. For you, avoiding nightshades might help reduce joint pain or other symptoms of inflammation. If you don't notice a difference, chances are that nightshades are not a problem for you and you can feel free to enjoy these otherwise nutritious foods.

Have you had success beating arthritis with diet changes? Post your story below in Comments.

If you have a suggestion for a future show topic send an email to nutrition@quickanddirtytips.com or post it on my Nutrition Diva Facebook Page. I answer a lot of listener questions in my free weekly newsletter, so if you’ve sent a question my way, be sure you’re signed up to receive that

Potato image courtesy of Shutterstock

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