Perhaps you avoid nightshades yourself, or have noticed a lot of people do? Is there any reason for avoiding them?
Nightshades are in the Solanaceae family, which comprises 2,800 types of plant. The common nightshades include potatoes (which aren't consumed on a Paleo regime, so I won’t be talking about them), tomatoes, all types of peppers/ capsicum, eggplant, tomatillos, tamarios, paprika and cayenne. Sweet potatoes are related, but belong to the Convolvulaceae family, so aren't classed as a nightshade. Similarly black pepper is not classed as a nightshade as it belongs to the Piperaceae family.
Nightshades contain alkaloids, which the plant produces as a defence mechanism. Some alkaloids have been shown to interact with nerve activity and inflammation, which may impact conditions such as arthritis and gout, as well as gut irritation. Many people have no sensitivities to Nightshades, but those that do may find avoidance very beneficial. Cooking decreases the alkaloid content by up to 50%, so for those with border line sensitivity, this can be a good option.
If you think you may have a sensitivity, eliminating nightshades for 30 days before reintroducing should give a clear indication as to the effect these plant have on you. If you find you do have a sensitivity, you might chose to avoid them on a more permanent basis.
Do you eat Nightshades? Do you have a sensitivity to them?