No, not for everyone. In 7 randomized trials with 465 people, eating tomato did not raise CRP or IL-6, and it lowered TNF-alpha. Potato and chili pepper trials found no harm either. The arthritis version of the claim rests on patient reports. The first trial to test it was only registered in 2023.
The claim
Nightshades are inflammatory. Cut tomatoes, peppers, eggplant and potatoes, and your joints, your gut and your blood work will settle. The strong version says this applies to everyone. The softer version says it applies to anyone with arthritis or a gut condition.
The family is real, and it is big: over 2,000 plants, including the four on your plate and a few famous poisons. That mix is a large part of the story.
Where it comes from
Three roots, and each one holds a grain of truth.
Daily potatoes lowered small-intestinal permeability and after-meal endotoxin in adults with metabolic syndrome, the opposite of a damaged gut lining.From a 2022 randomized trial in Nutrients
The alkaloids. Nightshades make glycoalkaloids, chemicals that defend the plant against being eaten. In lab studies these compounds disrupt the gut lining and may switch on mast cells, immune cells that drive allergic inflammation. Tomatine, the tomato's version, sits in small amounts in unripe fruit and drops as the tomato ripens. The same family gave medicine the drug atropine. That is one reason the word "nightshade" sounds like a warning.
The arthritis folklore. People with rheumatoid arthritis (RA) have long reported that tomatoes and eggplants make them feel worse. The idea behind it is that solanine, a potato glycoalkaloid, might add to bone and joint damage. It has been repeated for decades. It was never put to a randomized trial until a 40-person study was registered in 2023. And in a 2017 survey, when 217 people in a US arthritis registry were asked which of 20 foods changed their symptoms, the ones blamed most often were sugary soda and desserts.
Elimination-diet culture. In a 2023 survey, 171 people with inflammatory bowel disease (IBD) at two Swiss clinics answered questions about food. About 3 in 4 believed diet played a role in their disease, more than half had changed what they ate, and 39% had never had dietary advice from a doctor or dietitian. Into that gap step the food lists. Nightshades are on most of them.
What the evidence shows
Here is what happened when researchers fed people nightshades and then checked their blood. CRP (C-reactive protein), IL-6 (interleukin-6) and TNF-alpha are proteins that rise with inflammation.
Tomatoes. A 2022 meta-analysis pooled 7 randomized trials with 465 adults. Tomato intake did not change CRP or IL-6, and it lowered TNF-alpha. We covered those trials in an earlier article. None found a rise.
Potatoes. Potatoes carry the most glycoalkaloid worry, so the gut test matters most. In a 2022 crossover trial, 27 adults with metabolic syndrome ate a guidelines-based diet for 2 weeks with daily potatoes, and again with bagels. The researchers measured how leaky the small intestine was with a sugar test, and how much bacterial endotoxin reached the blood after a meal. Both were lower on the potato diet. That is the opposite of a damaged gut lining.
A 2020 crossover trial gave fifty healthy adults a non-fried potato side dish every day for 4 weeks, and a refined grain dish for another 4. Nothing measured got worse, and diet quality, potassium and fiber all went up.
Studies that only watch what people eat look worse for potatoes. A 2020 map of 121 of them linked higher intake with higher blood pressure and body weight, and the fried form with most heart and metabolic risks. A review of clinical trials, the same authors note, found no convincing link at all. Fries are the problem in that data. The plant is not.
Peppers. A 2017 randomized trial gave 42 adults with low HDL cholesterol 4 mg of capsaicin a day, as pepper skin powder, for 3 months. HDL rose and CRP fell moderately compared with the control group. A 2022 umbrella review then gathered eleven reviews on spicy food and chili peppers, 27 findings in all. Its verdict: unclear overall but typically safe, with lower death and heart disease rates in some studies and higher stomach and esophageal cancer rates in others. Heat has its own story. Inflammation is not the headline of it.
Eggplant. We found no human trial that fed people eggplant and measured inflammation. The claim stands on nothing, either way.
Nightshades as a group. This is where the gap sits. The 2023 review on nightshades and gut disease calls the human data limited and builds its case from lab work on glycoalkaloids and mast cells. The RA trial protocol says plainly that no randomized trials of nightshades in RA exist. Its 8-week study of 40 people is the first. It has not reported.
What has been tested in RA is diet more broadly. A 2021 review of 70 human studies found that high-dose omega-3 fats reduced disease activity and that the Mediterranean diet improved some measures. Elimination diets gave responses the authors called "very individualized." The 2022 American College of Rheumatology guideline made 28 recommendations to sit alongside drug treatment. Exercise got the only strong one. Three weaker ones covered diet.
Our verdict
The claim comes in several sizes. Here is each one against its best human evidence.
| Version of the claim | Best human evidence | Our grade |
|---|---|---|
| Nightshades are inflammatory for everyone | 7 tomato trials, 465 people: CRP and IL-6 unchanged, TNF-alpha lower. Capsaicin trial: CRP lower. | Not supported |
| Glycoalkaloids damage the gut lining | Lab studies only. The one human trial that measured it found less gut leakiness with daily potatoes. | Not supported |
| Nightshades make arthritis worse | Patient reports. The first trial, 40 people, was registered in 2023 and has not reported. | Early |
| Nightshades worsen IBD or IBS | A 2023 review calls the human data limited. The mast cell link is an idea, not a finding. | Early |
| Potatoes harm metabolic health | Trials: no convincing evidence, and no change over 4 weeks. Fried potatoes are linked to worse numbers. | Not supported, non-fried |
| Some individuals react to nightshades | Allergies and cross-reactions are on record. Elimination diet responses are "very individualized." | Emerging |
"For everyone" is the part that fails. "For me" is a question only your own test can answer.
What to do with this
Tick what you'll try this week. Your picks stay on this device.
you have a known food allergy or a history of cross-reactions; you have IBD and are planning any elimination diet; you are pregnant or feeding a child; or you take medicine for arthritis or a gut condition. Keep taking it as prescribed and ask before changing anything.
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How this article was made
Researched and written from 13 peer-reviewed papers. Our automated check matched every claim against the exact words of its source, confirmed every paper exists in PubMed, and found none retracted. Checked November 3, 2026. Not individually reviewed by a doctor. Photos are illustrative; the people in them are not patients or readers.
Grades run Strong, Moderate, Emerging, Early and Not supported, and the grade decides the words we may use. How we grade evidence · Medical disclaimer
Sources
- ReviewNightshade Vegetables: A Dietary Trigger for Worsening Inflammatory Bowel Disease and Irritable Bowel Syndrome?Kuang R, Levinthal DJ, Ghaffari AA et al. Dig Dis Sci, 2023.PubMedFull paper
- Randomized trialThe evaluation of nightshade elimination diet (NED) on inflammatory and rheumatologic markers of rheumatoid arthritis patients: study protocol for a randomized controlled trial.Golmohammadi A, Hosseinikia M, Sadeghi MK et al. Trials, 2024.PubMedFull paper
- Meta-analysisEffect of tomato consumption on inflammatory markers in health and disease status: A systematic review and meta-analysis of clinical trials.Widjaja G, Doewes RI, Rudiansyah M et al. Clin Nutr ESPEN, 2022.PubMedFull paper
- Randomized trialDaily Inclusion of Resistant Starch-Containing Potatoes in a Dietary Guidelines for Americans Dietary Pattern Does Not Adversely Affect Cardiometabolic Risk or Intestinal Permeability in Adults with Metabolic Syndrome: A Randomized Controlled Trial.Cao S, Shaw EL, Quarles WR et al. Nutrients, 2022.PubMedFull paper
- Randomized trialDaily intake of non-fried potato does not affect markers of glycaemia and is associated with better diet quality compared with refined grains: a randomised, crossover study in healthy adults.Johnston EA, Petersen KS, Kris-Etherton PM Br J Nutr, 2020.PubMedFull paper
- Randomized trialCapsaicin Supplementation Improved Risk Factors of Coronary Heart Disease in Individuals with Low HDL-C Levels.Qin Y, Ran L, Wang J et al. Nutrients, 2017.PubMedFull paper
- ObservationalPotato consumption and risk of cardio-metabolic diseases: evidence mapping of observational studies.So J, Avendano EE, Raman G et al. Syst Rev, 2020.PubMedFull paper
- Umbrella reviewSpicy Food and Chili Peppers and Multiple Health Outcomes: Umbrella Review.Ao Z, Huang Z, Liu H Mol Nutr Food Res, 2022.PubMedFull paper
- StudyDiet and Rheumatoid Arthritis Symptoms: Survey Results From a Rheumatoid Arthritis Registry.Tedeschi SK, Frits M, Cui J et al. Arthritis Care Res (Hoboken), 2017.PubMedFull paper
- StudySurvey of dietary beliefs and habits of inflammatory bowel disease patients.Verdina M, Seibold F, Grandmaison G et al. Clin Nutr ESPEN, 2023.PubMedFull paper
- ReviewReview on toxicology and activity of tomato glycoalkaloids in immature tomatoes.Wang LH, Tan DH, Zhong XS et al. Food Chem, 2024.PubMedFull paper
- Systematic reviewRheumatoid arthritis and dietary interventions: systematic review of clinical trials.Philippou E, Petersson SD, Rodomar C et al. Nutr Rev, 2021.PubMedFull paper
- Guideline2022 American College of Rheumatology Guideline for Exercise, Rehabilitation, Diet, and Additional Integrative Interventions for Rheumatoid Arthritis.England BR, Smith BJ, Baker NA et al. Arthritis Rheumatol, 2023.PubMedFull paper
