Nightshade Vegetables: Is The Tomato Toxic?

Nightshade vegetables have become bone of contention in health circles recently; for all the talk about lycopene and beneficial antioxidants, members of family Solanaceae have been blamed for causing arthritis, various other types of inflammation, and a wide range of allergies.

Since this family of plants contributes some of the most delicious culinary vegetables raw foodists eat, such as tomatoes (which I love devouring in massive quantities), ground-hugging, tangy tomatillos, tamarillos (which first repulsed me and then won my heart when I discovered them at a market high up in the mountains of Bali), sweet peppers, and some staid members like the eggplant, it would be a shame if we needed to avoid them for health reasons.

So what's the verdict?

Nightshade Vegetables: What's Wrong With them?

If you were a boy scout or attended summer camp, a smart counselor may have warned you away from a number of berry-growing bushes you discovered on hikes through the woods.

At least some of those plants were probably of the Solanaceae family, and the term deadly nightshade, often applied to them, wasn't a mistake. A number of these wild-growing nightshade vegetables can be highly toxic. They contain alkaloids - chemical substances acting as natural pesticides to drive off, incapacitate, or kill predators -, and glycoalkaloids, which have been known to poison people eating green, uncooked potatoes (potatoes are also a nightshade).

The fruit and leaves of these plants still poison and kill people in the modern era (1), (2).

Nightshade Vegetables TamarillosFor millenia people have eaten nightshades specifically to be poisoned and experience hallucinations. The famous mandrake root is one example. The steroid alkaloids in these plants can block certain nerve activity, which leads to muscle twitching, temporary paralysis, difficulty breathing, and various changes to audio and visual perception.

A number of animal studies have found livestock eating wild nightshades, including Solanum malacoxylon, and Solanum sodomeum (the Solanum genus also contains eggplant, tomatoes, and peppers), are frequently sickened by arthritis-like inflammation or killed (3) (4).

Nightshade Vegetables: So What About The Tomato?

Not all nightshade vegetables were created equal, and many of the harmful properties found in wild members of of the family are absent or greatly reduced in their cultivated counterparts. The edibles we're interested in are members of two genera: Capsicum and Solanum, or the pepper genus and potato/tomato/eggplant genus, respectively.

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Before you go uprooting your tomato and pepper plants, keep in mind they have only a tiny fraction of the alkaloid content of the wild-growing deadly nightshades and that glycoalkaloids are reduced during a fruit's ripening process.

Our ancestors weren't stupid, and would have noticed any large-scale problems arising from the introduction of tomatoes, peppers, and other nightshades into their diets. Today, large swaths of humanity eat large amounts of nightshades without apparent negative side effects.

Yet there is a minority of people who've found the (inaptly named) nightshade diet containing no members of the family have brought them relief from certain symptoms. Many claim tomatoes and arthritis are related, for instance. It's become popular for doctors and nutritionists to suggest those suffering from arthritis do a trial elimination of the Solanaceae family, along with other known inflammation-causing foods.

But is there any evidence these diets work for humans?

Nightshade Vegetables: Any Evidence That Nightshade Diets Work?

Nightshade Vegetables EggplantsThere's plenty of anecdotal evidence indicating problems with nightshade vegetables. Surveys have found many people suffering from arthritis believe they find relief when nightshades are eliminated from their diet (5), and a trip to many health forums on the internet will put you in contact with people who blame them for causing all manner of diseases.

Nightshade diets haven't fared nearly as well in peer reviewed trials, however.

The majority of dietary studies looking at the effect of nightshades have also involved the elimination of other foods known to cause inflammation, such as dairy and gluten, making it hard to be sure exactly what's causing the problem, even if the the elimination diets work..

One study that eliminated dairy, red meat, citrus, peppers, tomatoes, alcohol, and coffee (the Dong diet) as part of a double-blind placebo controlled trial found there was no statistical improvement difference between the Dong followers and the controls. Notably, though, two patients on the dong diet did see significant improvements, but their gains disappeared after eating meat, dairy, and alcohol (6).

A more effective treatment for arthritis is fasting patients and then placing them on a vegan diet, but this still only improved 25% of the patients (7).

Overall, no one has so far shown a solid link between the elimination of nightshades and improvements in inflammation-based diseases.

Nightshade Vegetable Exclusion: Worth A Shot?

I think it's likely a sizable minority of people are allergic to one or more nightshades or suffer from sensitivity to alkaloid chemicals in general, an idea that has some backing (8). The general alkaloid sensitivity makes a lot of sense because while in one survey 37–43% of patients with inflammation-based diseases reported an increase in disease symptoms after intake of certain alkaloid-containing foods, there appeared to be no differentiation among the different types of diseases (9). This may mean the alkaloids are causing general inflammation which manifests itself in various ways among sensitive people.

Nightshade Vegetables TomatoesHowever, a large amount of people simply have nightshade allergies. One study of people consuming eggplant in India, where it's a major staple, found that nearly 10 percent of participants reported itchy skin and/or mouths after handling or eating eggplant (10).

Among those suffering from allergic reactions to food, which is believed to be more than 50 million people in the United States, between 1.5 and 16 percent have various allergic reactions brought on by tomatoes (11).

I'm fairly certain I have a minor tomato allergy myself. As much as I love tomatoes, I know when I eat them I frequently break out in small-scale itchy skin rashes and bumps. For years I wondered why I had periodic bouts of acne on my face until I tried eliminating them, which cleared up my skin.

Even so, their effect on me is relatively minor if I only eat them periodically, and I had no reservations about including them in several of the recipes in Savory Raw Dressings And Sauces.

I see no reason to suggest asymptomatic people avoid nightshade vegetables. If you believe they may be bothering you, it's easy enough to figure it out. Simply do a 30-day nightshade elimination diet. If you've found relief by the end of that trial, you have your answer.

Nightshade Vegetables: Following Up

Learn how to eat a healthy raw food diet.

Figure out how nightshade vegetables fit into among the foods you should embrace or avoid if you want health.

Want some amazing and healthy low-fat raw dressings to spice up your salad? Check out Savory Raw Dressings And Sauces.

Nightshade Vegetable Sources:

1) Solanine poisoning". Br Med J. 2 (6203): 1458–9. 1979-12-08. PMC 1597169. PMID 526812.
2) Alexander RF, Forbes GB, Hawkins ES (1948-09-11). "A Fatal Case of Solanine Poisoning". Br Med J. 2 (4575): 518. doi:10.1136/bmj.2.4575.518. PMC 2091497. PMID 18881287.
3) Wasserman RH. Active vitamin D-like substances in Solanum malacoxylon and other calcinotic plants. Nutrition Reviews 1975; 33:1-5
4) Davis GK. Effect of a nightshade (Solanum malacoxylon Send.) on calcium metabolism in livestock. In: Childers NF, Russo GM (eds.). The nightshades and health. New Jersey: Horticultural Publications, 1986; 144-157
5) Childers, N.F. M.S. Margoles. "An Apparent Relation of Nightshades (Solanaceae) to Arthritis" Journal of Neurological and Orthopedic Medical Surgery (1993) 12:227-231
6) Panush RS, Carter RL, Katz P, Kowsari B, Longley S, Finnie S. Diet therapy for rheumatoid arthritis. Arthritis Rheum 1983;26:462–71.
7) Sköldstam L. Fasting and vegan diet in rheumatoid arthritis. Scand J Rheumatol 1986;15:219–23.
8) Colbin, A. Food and Our Bones. New York, NY: Penguin Putnam Inc., 1998.
9) Haugen M, Kjeldsen-Kragh J, Nordvåg B-Y, Førre Ø. Diet and disease symptoms in rheumatic diseases—Results of a questionnaire based survey. Clin Rheumatol 1991;10:401–7.
10) Babu, B. N. Harish, P. A. Mahesh. Y. P. Venkatesh. A cross-sectional study on the prevalence of food allergy to eggplant (Solanum melongena L.) reveals female predominance. Clinical & Experimental Allergy 38(11):1795–1802, 2008.
11) Westphal S, Kolarich D, Foetisch K, Lauer I, Altmann F, Conti A, et al. Molecular characterisation and allergenic activity of Lyce2 (beta-fructofuranosidase), a glycosylated allergen of tomato. Eur J Biochem 2003;270: 1327–1337.

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