What You Should Know About Nightshades and Arthritis

Nightshade fruits and vegetables — tomatoes, peppers, eggplant and potatoes — have sparked debate for decades. The point of contention? Whether or not these foods can cause flares in some people with autoimmune disease, including inflammatory forms of arthritis such as rheumatoid arthritis and psoriatic arthritis. People who feel worse after eating them clearly think they can. Many doctors say that’s hooey. There’s little scientific evidence on either side, but a lot to be said for lived experience.

What Are Nightshades?

They’re a big family of around 2,500 plants, diverse enough to include potatoes, tobacco and the hallucinogen datura. Many nightshades are inedible and some, like bittersweet nightshade, a tomato relative, are notoriously toxic. All contain small amounts of a toxic compound called solanine, which helps the plants repel insects and can be poisonous to both humans and animals.  Cattle, sheep and pigs are particularly sensitive to solanine and can die from eating the vines and leaves of tomatoes and potatoes. No research suggests this level of toxicity in humans, though you want to steer clear of potatoes that have turned green; they’ve developed exceptionally high amounts of solanine and aren’t safe to eat.

What the Research Shows

Decades-old mouse studies reported that solanine damaged the gut lining and increased intestinal inflammation in colitis, a type of inflammatory bowel disease. But the latest research in mice found the opposite. Several studies suggest that purple potatoes and goji berries — also a nightshade — reduce inflammation, intestinal permeability (impaired gut barrier function) and harmful gut bacteria. These are all problems common in people with rheumatoid arthritis and other inflammatory forms of the disease.

When evaluating these studies, it’s important to keep in mind that mouse studies rarely translate well to human beings.

What You Can Do

The nightshade issue can be particularly confusing for patients because doctors and dieticians often advise not cutting these foods from your diet for nutritional reasons. But there are hundreds of nutritious fruits and vegetables; you don’t have to eat nightshades to be healthy. Here are some options:

If you suspect you may be sensitive to nightshades, don’t eat them for two weeks. Then slowly introduce them back into your diet. Allow about three days between each one. “If these foods seem to increase your symptoms, avoid them and substitute other sources of key nutrients,” says Lona Sandon, PhD, associate professor of clinical nutrition at the University of Texas Southwestern Medical Center in Dallas. People can be sensitive to many foods, and anecdotally, a lot of people are sensitive to nightshades.

Try to stick to an anti-inflammatory or Mediterranean-style diet that focuses on fresh fruits and vegetables (though not necessarily tomatoes and potatoes), healthy fats and moderate amounts of whole grains. You should avoid highly inflammatory foods like red meat, sugar and processed foods. Hundreds of studies have documented the benefits of this way of eating for inflammatory arthritis. It’s a dietary approach everyone can agree on. Also recommended for arthritis: fish oil, vitamin D and probiotics.