Walnut

Walnut is notable for histamine, salicylate, nickel and oxalates. Clear on tyramine, sucrose, FODMAPs, lactose, oligosaccharides, sorbitol, fructose and gluten.

Yes — walnut is high in histamine. Walnut is one of the two nuts the elimination lists name, with the cashew, and this axis puts it highest of the group for that reason. What it is not is a nut that becomes an amine problem by going rancid: rancidity is the oil reacting with oxygen, and oxidised oil yields aldehydes and off-flavours, not amines - those need water and bacteria, and a dry kernel offers neither. Walnut oil is the most unsaturated of the common nuts, so it does go off fastest. Buy them in the shell or from a cold shelf for that reason, which is a good one and a separate one. One measurement backs the position rather than the list: Yilmaz determined serotonin in twelve nuts and the raw walnut came out highest of all of them, 155 µg/g against 0.05 for the pine nut.

Yes — walnut is high in salicylate. Walnut carries salicylate and no measurement places it: the one survey that put 112 foods through GC-MS for this axis states that the walnut is not among them, and the surveys that do cover nuts publish group ranges rather than a value for any single kernel. The lever a reader actually has is the portion — walnuts are eaten by the handful, and unlike an apple there is no peeling and no cooking step that takes salicylate out of a kernel.

Yes — walnut is high in nickel. Walnuts are high in nickel, and unlike most nuts they are usually eaten with the skin, which is the fraction where trace metals concentrate.

Walnut contains only low levels of oxalates. Walnuts carry less oxalate than most nuts, but the group as a whole is not a low-oxalate food — almonds and cashews are well above them. They arrive mostly as halves inside baking, where the portion is decided by the slice rather than by the nut. Amounts vary by brand and recipe, so always check the label of the exact product.