Some people believe plants in the nightshade family cause inflammation, joint pain, digestive discomfort, and other problems. Potatoes can cause digestive distress, especially if they are green, damaged, or sprouting, but there is scant evidence that they cause inflammation or joint pain.
One randomized controlled trial tested the impact of potatoes on markers of inflammation, reporting that a single meal of potatoes led to higher circulating levels of the inflammatory cytokine interleukin-6 in lean women but not women with obesity, and higher circulating levels of the inflammatory cytokine tumor necrosis factor-alpha (TNF-⍺) in women with obesity but not lean women, relative to All-Bran cereal in the six hours following the meal.[1] This result should be viewed with caution since the study reports many outcomes without statistically correcting for multiple comparisons, increasing the probability that some of the findings are due to chance. It is also not clear how potatoes would have fared if they had been compared to other types of food. A 4-week randomized controlled trial, meanwhile, found potatoes and refined grains did not clearly differ in their effect on the inflammatory marker C-reactive protein (CRP).
Randomized controlled trials tend to suggest that eating tomatoes or tomato extracts, another food in the nightshade family, reduce markers of inflammation, although not all findings have been consistent.[2][3][4][5][6]
Nightshades, including potatoes, contain glycoalkaloids, which can cause digestive distress. These are only present in potentially dangerous amounts in potatoes that are green, damaged, diseased, and potato sprouts. Peeling potatoes removes most of their glycoalkaloid content.[7]