Nightshade vegetables and fruits belong to the Solanaceae family of plants. The edible nightshades include tomatoes, peppers, eggplants and potatoes. Many members of the family contain pharmacologically active components and have been used in traditional medicine, as hallucinogens, as anesthetics, and poisons. Tobacco is also a nightshade.
People with arthritis, including rheumatoid arthritis (RA) often ask whether nightshades should be avoided. If we look at the information on the topic from websites of various arthritis foundations around the world, you’ll find statements like this:
“Some people believe nightshade fruits and vegetables may worsen inflammation and arthritis, but scientific evidence does not support this.”
(Source: https://www.medicalnewstoday.com/articles/321745)
Others include more open-minded statements like this (source: https://www.arthritis.org/health-wellness/healthy-living/nutrition/anti-inflammatory/how-nightshades-affect-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.”
Where has the idea that nightshades affect arthritis come from, and are there any studies testing whether they affect arthritis?
First – I carried out a PubMed search – this is a pretty good place to go for science. After searching for any study at all that tested negative effect of nightshades in arthritis, I came up with a big fat zero.
I did however find two study using surveys, one in people with Gout, the other Psoriasis
“Positive association of tomato consumption with serum urate: support for tomato consumption as an anecdotal trigger of gout flares” (https://pubmed.ncbi.nlm.nih.gov/26286027/):
2051 New Zealanders with clinically ascertained gout were asked about trigger foods – Results: “Seventy one percent of people with gout reported having ≥1 gout trigger food. Of these 20% specifically mentioned tomatoes, the 4th most commonly reported trigger food. There was association between tomato intake and serum urate levels”
The next – a survey of people with psoriasis:
“Dietary Behaviors in Psoriasis: Patient-Reported Outcomes from a U.S. National Survey “
A total of 1206 psoriasis patients from the US National Psoriasis Foundations responded to the survey which asked what foods and diets they found helpful.
Results: “The percentage of patients reporting skin improvement was greatest after reducing alcohol (53.8%), gluten (53.4%), nightshades (52.1%), and after adding fish oil/omega-3 (44.6%), vegetables (42.5%), and oral vitamin D (41%). Specific diets with the most patients reporting a favorable skin response were Pagano (72.2%), vegan (70%), and Paleolithic (68.9%).” (Pagano diet: https://www.scribd.com/document/526405905/Pagano-Diet)
In Rheumatoid arthritis – there are no studies that specifically test the effect of nightshades. The only study I am aware of that mentioned they specifically removed nightshades as part of the exclusion diet is the ITIS study.
You can read about the protocol here “Design of an anti-inflammatory diet (ITIS diet) for patients with rheumatoid arthritis” https://www.sciencedirect.com/science/article/pii/S2451865420300089
The reason that nightshades are removed is stated: “Solanaceae vegetables contain glycoalkaloids. Glycoalkaloids have been reported to affect intestinal permeability” The references link to research on the effects of nightshades on intestinal permeability, via tests on intestinal tissue, in mouse studies and one human study. None however, tested the effect in arthritis.
Results from the ITIS study which included 20 people with RA, show around half had considerable improvement in 2 weeks, with reduction in pain and fatigue. However, nightshades are not isolated from all the other dietary changes so the effect of the nightshade removal can’t be judged from this study. “Baseline microbiome and metabolome are associated with response to ITIS diet in an exploratory trial in patients with rheumatoid arthritis” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9269999/
One study is in the pipeline – to test the removal of nightshades in RA
When we look at the clinical studies register – we do find one study, here is a pre-print of the study protocol https://www.researchsquare.com/article/rs-3027968/v1 . The paper and references are useful for a more in depth look at the theory behind the reason for carrying out a study testing nightshade elimination. “The evaluation of nightshade elimination diet (NED) on inflammatory and rheumatologic markers of rheumatoid arthritis patients: study protocol for a randomized controlled trial”
Taking a look back at history for clues:
Historically the idea that nightshades affected arthritis came from two places, Ayurvedic medicine and work from Dr Norman Childers a professor in horticulture.
In Ayurveda, their removal is recommended for arthritis “Nightshades are believed to trigger an inflammatory response (also contains oxalates) in the body especially in the joints and are very aggravating to vata and pitta.” https://www.geetavara.co.uk/blog-2/nightshades-ayurveda
Dr Norman Childers probably had the greatest early influence on the removal of nightshades from the diet for arthritis. I’ve included some excerpts from the article. He writes about it here: https://www.thefreelibrary.com/The+arthritis+and+nightshades+story.-a0110263404
Dr Normal Childers had suffered from arthritis for over 50 years in his arms back and neck. He also suffered diverticulitis and “non-cancerous breast operations” (I’m not exactly sure what that means!).
Dr Childers writes “Being in research, I asked the surgeon, the late Dr. Rudolph Matflerd in 1964, “What causes these sharp intestinal pains? You can name it, Doctor, but what is the cause?” He answered. “We don’t know. We think it may be hot pepper irritating the intestinal walls!” Ah, a lead! Being a horticulturalist, I knew that hot pepper is a nightshade and has the above relatives. So, the author started a diet of no nightshades, including no tobacco. Surprise! No bowel or breast problems recurred. Arthritis disappeared.”
He continues “But this was only one case and no report was made for fear of repercussions and impact on an established industry, professions, marketing, and the millions of people who love these foods.”
His secretary Charlotte O’Sullivan also tried the nightshade free diet and had similar results; word spread among the other secretaries. This led to an idea to carry out an informal study and ask people to try the diet and report their results.
“Eventually, they (the secretaries) asked, “Why don’t you do something about this to help other sufferers?” So, by placing a few ads in horticultural magazines, getting help from Organic Gardening magazine in Emmaus, Pennsylvania, and making contact with arthritic friends who contacted their friends, we finally had a significant number of cooperators. In 1974, a postcard arthritic survey was sent to over 2,400 cooperators that brought a 30% response, showing over 72% positive results with some cooperators able to abandon canes, walkers, and wheelchairs (Table 1). Sherman of the Rodale Organic Gardening Faculty, Emmaus, Pennsylvania, made a survey of over 3,000 recruited arthritics, getting a 9.7% return with 87% reporting a positive response. Fifteen percent reported over 85% relief. Twelve percent reported no results. Ages ranged from 20 to 80 years.
In 1977, a book was published, Nightshades and Health by N. F. Childers and Gerard M. Russo to announce the “No-Nightshades” positive survey and to recruit more cooperators. In 1985 and 1986, a four-page survey was designed by Foundation advisors, Oscar M. Kreusi, MD and Edwin Wendlocher, Sr. It was sent to 5,000 current book holders bringing only 434 replies or an 8.6% return, showing a 68[percent] positive response. Those who complied rigidly with the diet reported 94% relief.”
The tables can be found in the publication “An apparent relation of nightshades (Solanaceae) to arthritis” The Journal of neurological & orthopaedic medicine & surgery. Childers NF and Margoles MS. 1993, Volume 14, pages 227-231.
I tracked down the Prevention Magazine article: Here is the entire article.
“Arthritis: What Works” Another survey study, by Arthur Klein and Dava Sobel:
Another person to carry out informal research on the effects of foods in arthritis was husband and wife team Arthur Klein and Dava Sobel. The authors developed a survey on arthritis management, and 1051 people responded. Of that total, 48 avoided nightshades to help control their arthritis. Their one page on the subject references Norman Childers, so his thinking is likely the source of the question. The results of their survey are compiled in the book “Arthritis: What works, treatments that really help”
In surveys in those with RA, some people said they experienced nightshades as triggering their symptoms. In a 2017 survey “Diet and Rheumatoid Arthritis Symptoms: Survey Results From a Rheumatoid Arthritis Registry” 7.5% said eggplant worsened symptoms, and 4% tomatoes. https://acrjournals.onlinelibrary.wiley.com/doi/epdf/10.1002/acr.23225
Specific foods that affect subjects’ RA symptoms, displayed as the percentage of subjects who eat the food
In a survey of 141 people with RA from India, a greater number of people experienced nightshades as exacerbating symptoms, 41 of 141 or 29% https://clinicalnutritionespen.com/article/S2405-4577(17)30195-X/abstract. Ayurveda principles which suggest nightshades should be avoided may be the reason more notice their effect.
Loren Cordain and the autoimmune protocol.
Loren Cordain wrote the popular book on the paleo diet, he also suggested other foods those with autoimmune disease should avoid because of the possible effect via the gut. He recommends that along with grains, legumes and dairy products, nightshades should also be removed. Both Robb Wolf and Sarah Ballantyne reinforced this message. Cordain and Ballantyne provide explanations as to why they should be avoided. Keep in mind that studies are often on cells and animals, and that we need clinical studies in humans to corroborate their effect in autoimmune diseases.
Here are links to their posts:
The why’s behind the AIP: Nightshades, by Sarah Ballantyne PhD https://www.thepaleomom.com/the-whys-behind-autoimmune-protocol/
Consumption of nightshade plants, human health and autoimmune disease, Loren Cordain PhD https://www.texasgrassfedbeef.com/pub/media/sites/default/files/pdf/consumption_of_nightshade_plants_human_health_and_autoimmune_disease_cordain.pdf
Studies are needed!
We just do not know to what extent people suffering from various types of arthritis need to avoid nightshades, we simply have no studies one way or the other. The only way you will know if they affect you is by
- Keeping a food diary and note if symptoms occur after eating nightshades
- Eliminate one or all nightshade fruit and vegetables, observe whether your symptoms reduce
- Re-introduce one type of nightshade at a time, one a week and observe if your symptoms increase.
