Question: do plants from the nightshade family cause inflammation and aggravate arthritis?

The straight answer: no

The facts: The Solanaceae family of flowering plants is often maligned for their supposed contribution to inflammation. More commonly referred to as nightshades, certain fruits (tomatoes, goji berries, gooseberries, etc), vegetables (peppers, potatoes, eggplants etc) and spices (cayenne and paprika) from this category produce solanine, an alkaloid compound that acts as a nerve poison on insects that feed on these plants.

However, the notion that solanine can be toxic to humans hasn’t been proven yet. Moreover, they’re present in the stems and leaves of nightshades, which aren’t edible anyway. Some studies conducted on mice have shown them to cause an increase in inflammation markers, but not inflammation itself.

Interestingly, the fruit of some nightshade plants, such as goji berries, Cape gooseberries (Physalis), and garden huckleberries are quite high in antioxidants, which actually assist in reducing inflammation. Another member of the nightshade family, the chilli pepper, contains capsaicin, which is a strongly anti-inflammatory compound and could be beneficial to arthritis sufferers provided they are not sensitive to the peppers.

Tomatoes are a highly concentrated source of biotin (necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids) and lycopene (a carotenoid phytonutrient that prevents heart disease and certain types of cancer). Eggplants contain the antioxidant nasunin and chlorogenic acid that helps lower LDL (so-called bad cholesterol) and fights the free radicals that cause cancer; and potatoes contain alpha-lipoic acid, which can help control blood sugar.

Some followers of macrobiotic diets believe nightshades to be high in oxalic acid, which inhibits the absorption of calcium and can weaken bones and lead to osteoporosis. However, Stephanie Atkinson, a member of the scientific advisory committee for Osteoporosis Canada, says that while oxalates are known to bind calcium in the intestine, reducing calcium absorption, this occurs only when calcium intakes are very low and oxalate intakes very high.

According to Atkinson, nightshades are not high in oxalic acid. The alkali contributed by vegetables and fruits is beneficial for bones.

There are many documented reports that people with arthritis have less stiffness and fewer arthritic symptoms when they don’t eat nightshade vegetables. Some people can be sensitive to these vegetables and to solanine as well. However, only a small number of people are so affected and the phenomenon hasn’t been documented scientifically. Most of the evidence is just anecdotal. Proving sensitivity to foods is very hard to test and is usually done by assessing how it affects symptoms.

Denise Fair, an accredited dietitian at Central Health Medical Practice, says: “Many people when they do go off nightshade vegetables change other aspects of their diets, most notably adding omega 3 fats.