Wisdom Wednesday: Nightshade Vegetables

Nightshades are plants in the Solanaceae family. There are more than 3000 varieties, a few of which are fruits, vegetables and herbs in our diet. The common nightshade foods include: tomatoes, peppers, eggplant, potatoes, huckleberries, pimento, paprika, cayenne pepper, and Chili powder.

Nightshades are often used in sauces and seasoning blends, including ketchup, hot sauce, steak sauce and curry.

Lectins are the proteins common to all nightshade plants. They bind that carbohydrates that also can create food sensitivities.

However, the clinical correlation between nightshades and food sensitivity may have more to do with other phytochemicals found in these plants. The alkaloids and glycoalkaloids that occur in nightshades are naturally occurring pesticides. Solanine, capsaicin and nicotine are the most significant of these compounds.

Many nightshades are highly toxic and aren’t meant to be eaten. The herb belladonna is a nightshade that Juliet uses to fake her death in Shakespeare’s Romeo and Juliet. Glycoalkaloid poisoning has been reported and is an irritant to the gut.

Sunlight promotes solanine formation, so it’s important to store potatoes away from natural light. Potatoes that have sprouts or a greenish hue, taste bitter, or have a mushy texture should not be eaten.

Both glycoalkaloids and lectins have been shown to increase intestinal permeability of the small intestine contributing to leaky gut. This in turn may stimulate an autoimmune response to any protein or carbohydrate that slips across the barrier without full digestion.

Capsaicin is actually used to reduce abdominal pain (red pepper powder) but can also irritate the lining of the gut.



There is also anecdotal evidence that the nightshades can increase joint pain. It has been proposed that the calcitriol (vitamin D) in these plants may cause calcium to be deposited into the joints causing pain and stiffness. I suspect that the joint inflammation is a result of molecular mimicry that can occur with any autoimmune disease rather than a calcium imbalance from excessive vitamin D.

The Paleo diet movement has added the nightshades to the list of foods to avoid. Clinically, I find that eliminating the processed foods like ketchup and sauces that contain nightshades is of more benefit than targeting nightshades specifically. The concept of single ingredient foods rather than processed foods is central to the Paleo way of eating.

The Bottom Line:
Nightshades can be problematic for some people and may contribute to food allergy and food sensitivities but probably indirectly. Of the five food groups we have looked at in the past six weeks, it is by far the least significant offender. However, I do on occasion find oral challenge to nightshades reactive and have recommended those patients try to avoid nightshades whenever possible.