Fish oil, cod liver

Cod liver oil is extracted from the livers of cod and is traditionally taken by the spoonful rather than cooked with, a habit with roots in Scandinavian and British households. Plain versions have a strong, distinctly fishy flavor, which is why many bottled products are flavored with lemon, orange or mint to make swallowing a spoonful easier, and capsule forms are common for the same reason. In a handful of traditional Nordic and Icelandic dishes it's drizzled over cooked fish or potatoes, but for most people today it's a bottle kept for taking straight rather than an ingredient stirred into recipes.

Because it's an oil rich in compounds that degrade with heat, light and air, cod liver oil should be kept refrigerated in its original opaque or dark bottle once opened, and used within the timeframe printed on the label. Like any pure oil it's calorie-dense, 902 calories per 100 grams and entirely fat, with no protein or carbohydrate. Its defining feature is vitamin A, an extraordinary 3333% of the Daily Value per 100 grams, which is why even the small teaspoon doses on a typical bottle's label are treated as a single serving rather than something to pour freely.