What you eat can play a role in nearly everything your body does, so it’s no surprise that diet can affect many chronic diseases, including arthritis. Emerging research on the body’s inflammation response has shown a connection between diet and inflammatory markers, but there are still many unknowns about exactly how this relationship plays out in inflammatory forms of arthritis like rheumatoid arthritis and psoriatic arthritis.
Of course, that hasn’t stopped reports from circulating about certain foods or food groups that can provoke an inflammatory response, triggering arthritis flares or other symptoms. One such report involves a group of vegetables known as nightshades. While the name might sound a little ominous, like an ingredient Harry Potter would need for potions class, the reality is a lot less exciting.
What Are Nightshade Vegetables?
Nightshades are the botanical classification for plants in the Solanaceae family, which include tomatoes, white potatoes, eggplant, and peppers (hot and bell). These vegetables do share genetic ties with toxic species — most prominently belladonna, which is known as deadly nightshade — but they tend to be pretty familiar to most people, and in general, enjoy a healthy reputation as low calorie, high-nutrient foods.
Why are they called nightshade vegetables? There is no definitive explanation although one theory — not proven — is that these plants were once believed to grow in the shade.
Nightshades and Inflammation: What’s Behind the Rumor
Experts aren’t sure why or when, but the idea that nightshade vegetables are linked to inflammation, particularly the kind involved in chronic disease like arthritis, evolved and still persists despite a lack of research-based evidence.
The theory revolves around the fact that all members of the nightshade family contain small amounts of a compound called solanine, says Amanda Waldron, RDN, a senior nutritionist at Brigham and Women’s Hospital in Boston, Massachusetts. In much larger amounts, solanine can be toxic — there have been rare cases where green potatoes have caused solanine poisoning, such as a 1983 incident in Alberta, Canada where 61 school children and staff were affected. But the amount of solanine found in nightshade vegetables we eat “doesn’t even come close to an amount that could do any damage,” Waldron says.
The Health Benefits of Nightshades
And in fact, Waldron points out, many of the foods that fall under the nightshade designation — which include not only vegetables but also spices like cayenne and paprika — are typically rich in nutrients and antioxidants that have been shown to fight inflammation.
In addition, many nightshades offer a host of other nutritional benefits, says nutritionist Julie Upton, RD, cofounder of Appetite for Health. Here are just a few of the more commonly consumed nightshade vegetables and the perks you could be missing out on if you avoid them:
Eggplant: Like other dark-colored produce, the eggplant’s deep purple skin is an indicator of beneficial phytonutrients. The flesh is rich in fiber and provides a good dose of potassium and magnesium, two minerals that help with muscle and nerve function.
Tomatoes: Although best known as a top source of lycopene, an antioxidant that has been shown to help protect against cardiovascular disease and certain cancers, tomatoes are also an excellent source of vitamins C and K and beta carotene, which your body needs to make vitamin A.
Potatoes: Spuds get a bad rap as carbs, but they’re really nutritional all stars. At just around 100 calories, a medium Idaho potato has four grams of filling fiber and is high in blood pressure-lowering potassium, along with many other B-vitamins and trace minerals.
Peppers: Bell peppers have high amounts of vitamin C, a potent antioxidant, and other antioxidants called carotenoids. Spicier varieties contain capsaicin, a compound that studies have shown can give you a slight metabolic boost.
“There’s certainly no evidence in literature regarding nightshade vegetables causing inflammation,” agrees Micah Yu, MD, a rheumatology fellow at Loma Linda University Medical Center in California, who has a special interest in nutrition and lifestyle to improve rheumatic diseases. Some of the confusion could be related to an understanding, or lack of, inflammation and its role in the body, Dr Yu says.
Understanding Inflammation: What Is It?
While it is true that many chronic diseases — from rheumatoid arthritis to cardiac disease — are driven by inflammation, it is also as natural a process in the body as digestion. “We do need inflammation as part of our normal healing process, and when we fight infections,” Dr Yu explains.
Basically, inflammation works like this: Your body’s immune system secretes proteins known as cytokines in response to various stimuli. Some of these molecules are pro-inflammatory and some are anti-inflammatory. You’ll see this reaction when you get a cut, for instance, and the are around it becomes red and swollen. Your immune system has released pro-inflammatory compounds to help with healing.
With some autoimmune diseases, however, this process gets thrown out of whack. The body’s immune system overeacts and causes inflammation without reason.
There is evidence that certain types of diets can trigger a hyperactive immune response, thereby contributing to inflammation, say Dr. Yu. “Most of our immune system is located in our gut,” he says. “When we eat food, it directly communicates with our immune system.”
In general, diets high in salt, refined sugars, processed foods, and red meat can have this pro-inflammatory effect, while high-fiber diets tend to have to opposite result. Plant-rich diets that are high in whole grains, fruits, and vegetables — including nightshades — tend to reduce inflammation.
Collectively, the immune system in your gut — you may have heard it referred to as the microbiome, a stronghold of trillions of bacteria — plays a role in inflammatory diseases like arthritis, says Dr Yu. “When it is not in balance, you have what is called gut dysbiosis, and that has been associated in the literature with multiple chronic inflammatory, including arthritis,” he says. After genetics, lifestyle and environment, including diet, can play a role in your risk of developing these diseases.
How to Eat to Reduce Inflammation
And that’s good news, because lifestyle is changeable. It’s not something you need a doctor’s prescription to alter. “You can’t cure arthritis or rheumatologic disease,” says Dr Yu. “But it is possible to put it in remission,” he says. Medication is a cornersone of treatment and is usually necessary to achieve remission in inflammatory arthritis. But making diet changes that help you lose weight if you need to and reduce your intake of pro-inflammatory processed foods can be an important part of your overall arthritis treatment plan.
While Dr. Yu allows that for some patients, eating nightshade vegetables could be tied to a food sensitivity or allergy, he stresses that would be an entirely individual reaction.
There is no science-based proof that nightshade vegetables exacerbate inflammation.
“I would recommend cutting out the more obvious inflammatory foods, things like refined sugar, high-salt foods, processed food, and red meat first,” he says. Then, he suggests, take a look at other lifestyle habits to make sure they’re healthy.
Lack of physical exercise, too little sleep, and too much stress have all been linked to inflammation as well. Only after ruling out all these issues would he suggest seeing a food allergy expert to determine whether you could have a sensitivity to nightshades or other foods. “Vegetables are so important for our overall health,” he says. “They contain anti-inflammatory fiber and phytonutrients.” It’s unlikely they would be the culprit before those other factors.
If you suspect you may have a food allergy or sensitivity, says Waldron, see a dietitian or other medical professional who can go through your history thoroughly. Don’t just start cutting foods out of your diet on your own, she says. You might just be throwing out foods or nutrients you need. Her best advise to anyone, whether you have arthritis or not, is to focus on eating a healthy diet of whole foods and cutting back on inflammation-causing fats, red meat, and refined sugar. “A well-balanced diet is strong defense against disease,” she says.