Potato

Potatoes are one of the cheapest, most calorically efficient staple foods on earth — and how they're prepared transforms their nutritional profile more than almost any other food. A plain baked potato with skin provides ~4g fiber, ~900mg potassium (more than a banana), and complete protein in small amount, all for ~160 kcal. The same potato fried into chips or thin fries delivers 3-4x the calories and a glycemic load comparable to white sugar.

Glycemic index and blood sugar

Boiled and baked potatoes have a high glycemic index (~70-90), which makes them a common trigger of blood sugar spikes for people with diabetes or insulin resistance. Cooling cooked potatoes (potato salad, leftover) converts some of the starch into resistant starch, which is fermented in the colon rather than absorbed — modestly lowering the effective glycemic load. Pairing potatoes with fat, protein, or acid (vinegar) also blunts the response.

Nightshades and solanine

Potatoes are nightshades. The general evidence that nightshades trigger arthritis or autoimmune symptoms is limited, but a subset of patients report consistent improvement when they eliminate them — potatoes belong on any nightshade-elimination trial. Green spots on a potato signal increased solanine (a glycoalkaloid that's mildly toxic at high doses); peel them off and the potato is fine. Sprouted potatoes have higher solanine throughout and should be discarded.

Sweet potatoes are not actually potatoes — they're from a different botanical family entirely (Convolvulaceae, not Solanaceae) and are not nightshades. People avoiding nightshades can usually eat sweet potatoes freely.