Conventional wisdom holds that nightshades cause inflammation, and particularly joint pain. Unfortunately, there are no lab tests to confirm this, nor are there any clear studies linking the two; it seems the connection is entirely anecdotal.
That’s doesn’t necessarily mean there’s nothing to it, though.
What Nightshades Are
Foods in the nightshade (or solanaceae) family include potatoes, tomatoes, eggplants, peppers, okra, and goji berries.
Spices in this family include paprika, chili powder, cayenne, and red (but not black) pepper.
A few herbs are also in the family, including belladonna (or deadly nightshade, a low dose herb which was historically used as a poison in higher quantities), and ashwagandha, otherwise a great calming adaptogen.
What all of these foods, spices, and herbs have in common is an alkaloid called solanine (hence the family name), produced like many anti-nutrients in plants as a natural pesticide. Most of it is concentrated in the leaves and stems of the plants rather than in what we’d consider the edible portion; the solanine found in the food itself is considered negligible.
But many of my patients are very sensitive. For them, might a “negligible” amount of solanine still be an issue?
Why Nightshades Might Be Problematic
The best explanation I can find for why trace amounts of solanine might be a problem goes back to the theory behind Dr Gundry’s Low Lectin Diet. Nightshades themselves contain lectins, as well as solanine, both of which are “anti-nutrients”, inhibiting the body’s ability to digest the food. If you’re not digesting your food properly, this causes two potential problems: first, you’re not able to extract its nutritional value, potentially leading to nutrient deficiencies. Second, the bacteria in your gut have to break your food down for you, leading to a shift in your microbiome population. What you feed grows, and the bacteria that feed on undigested food tends to be inflammatory. Molecular mimicry, or confused immune responses triggered by pathogenic organisms, is often associated with autoimmune disease, for instance).
There are a couple of studies that appear to bear this anti-nutrient/gut inflammation connection out. The alkaloids in potatoes are associated with intestinal inflammation and worsening Irritable Bowel Disease, for instance. Also, the spices in the solanaceae family have been shown to increase intestinal permeability at least to a minor degree.
Just as with any other food, there are also true nightshade (IgE) allergies, as well as IgG or IgA sensitivities. This is different from the kind of alkaloid sensitivity we’re discussing here though, and it can be found on testing.
If you suspect increased inflammation or joint pain after consuming nightshades, the mechanism likely goes back to gut inflammation (as so many things do).
Unfortunately there aren’t any labs that can be run at this point to confirm this kind of sensitivity, though. Your best bet is to try to avoid all nightshades for 3-4 weeks, and see if you notice symptomatic improvement. Generally improvement occurs around week 3 or 4 with a diet change, if it’s going to make a difference.
If you do notice improvement with nightshade avoidance, will you have to avoid them forever? Some people may choose to, but restoring gut integrity and balancing gut flora may enable you to reintroduce them later.