Healthy Eating

The Truth About Nightshades and Arthritis

Image of two eggplants with leaves

If you’re living with arthritis, chances are that you’ve read or heard that you shouldn’t eat foods in the nightshade family.  These include potatoes, tomatoes, eggplant, bell peppers, and spices like paprika and cayenne. While this view is fairly widespread, it has limited scientific basis. Let’s take a closer look.

A tough reputation

Cristina Montoya, a registered dietitian who lives with rheumatoid arthritis and Sjogren’s Syndrome, explains that nightshade vegetables contain a substance called solanine. Solanine is a type of alkaloid which is toxic in large amounts and can promote inflammation—but it’s almost entirely found in the leaves and stems of these vegetables, not the parts we eat. Research has not found any evidence that nightshades have a negative effect on joints or can make arthritis worse.

Food sensitivities

Some people are sensitive to different foods, including nightshades, whether or not they are living with arthritis. Montoya points to a couple of different possible scenarios. The first is oral allergy syndrome - when people who have allergies to tree or grass pollens also react to certain foods that have a similar protein makeup. Tomatoes are a common trigger. Another possibility is latex-fruit syndrome, when people who are allergic to latex also show sensitivity to some foods, including tomatoes and potatoes, which have similar proteins. However, these allergies or sensitivities don’t generally show up as joint pain or other arthritis symptoms, she says.

Cut it out

Of course, you know your body well.  Everyone is unique and will respond differently to different foods.  Though research hasn’t identified a connection between nightshades and inflammation, some people with arthritis report a worsening of symptoms after eating nightshade vegetables and fruit. If you think that nightshades are affecting your symptoms or otherwise making you feel unwell, you can try eliminating them from your diet for two weeks. Slowly reintroduce foods one at a time two or three days apart, says Montoya.

Before and during this process, keep a journal that includes what you ate, weather conditions, sleep quality and your state of mind, advises Montoya. “What is your emotional state? What is your mood at that time? Are you rushing the meal? Go beyond just writing down your symptoms; it's about the situation that is happening around that meal, and how you're responding to it,” she says. It’s also important to remember that you’re usually not eating just one food at a meal, like a big plate of tomatoes. “When I do this exercise with my patients, they realize that it's not really the nightshade causing the problem. It could be that along with that tomato, they had some slices of processed meat and processed cheese. And they didn't realize that was actually the culprit.”

Not everyone with sore joints who eliminates nightshades from their diet experiences pain relief and some evidence suggests that the nutrition content of nightshades may help with arthritis symptoms.  Eliminating nightshades could mean missing out on important nutrients that are beneficial to your health.

The benefits of nightshades

“They’re delicious!” says Montoya. “So flavourful and full of antioxidants.” Eggplants are low glycemic (they won’t raise your blood sugar quickly), rich in anthocyanins, an antioxidant that reduces inflammation, and are a good source of fibre. “We’re now starting to understand how fibre has a major role in nourishing the microbiome, that good bacteria. Eggplant with the skin on or potatoes with the skin on—all that fibre is actually feeding our healthy gut microbiome, which in turn is going to improve inflammation levels.”

Tomatoes and peppers are good sources of fibre, vitamin A and C, and lycopene. Cooked tomatoes, in particular, are an exceptional source of lycopene that’s more available to the body than when tomatoes are eaten raw. “If we look at a traditional Mediterranean diet and what they do with tomatoes, they're mostly eaten cooked, and they're cooked with olive oil, garlic and onions. That combination, it enhances the antioxidant lycopene in tomatoes. It actually provides a very potent anti-inflammatory food in combination.”

Potatoes are a source of vitamin C and potassium, which has anti-inflammatory properties. Potatoes can be a source of “resistant starch” too. “When you cook and cool potatoes, then reheat those potatoes or eat them in a potato salad the next day, that [starch] becomes resistant starch that bypasses the whole digestive process and goes strictly to feed bacteria in the colon. Again, these are health benefits and anti-inflammatory benefits,” she notes. Finally, on her Arthritis Dietitian blog, Montoya writes that “Capsaicin is an alkaloid found in cayenne and paprika, common spices in the Solanaceae family. It is a chili pepper extract that helps to relieve pain. A study found that dietary capsaicin actually reduced the inflammatory responses in people with obesity, meaning that it has potential usefulness in managing inflammation in inflammatory and autoimmune arthritis.”

The bottom line: “We really need to encourage our community with arthritis to not see a single food as an isolated thing. When you’re eating, let’s say one tomato, you're taking advantage of the full components of the tomato and the synergy—vitamins, antioxidants, the fibre. They are working together. So there's no such thing as one isolated nutrient or food compound that is going to trigger your inflammation levels. It's really to see food and nutrition as a whole,” says Montoya. She adds with a laugh, “Go, nightshades, go!”