Lemon

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

Lemon contains moderate levels of histamine. Lemon is one of the citrus fruits the elimination lists name, and it is a liberator rather than a source - it holds almost no histamine itself. The practical problem is that lemon is not a food you decide to eat: it is squeezed over fish, into dressings and into tea, so it arrives without being counted. Citrus is on the elimination lists as a liberator, but the current review attributes its symptoms to its other amines — putrescine above all — competing for the enzyme that clears histamine.

Lemon contains only low levels of salicylate. Lemon measures 6.7 mg of salicylate per kilogram, and the serve the survey used was 6 g - a squeeze - which delivers 0.04 mg, the smallest per-serve figure of any fruit measured. That gap is the whole argument of the paper: a food can be middling per kilogram and negligible in practice because nobody eats a kilogram of it. The zest is the part to watch, being skin. Amounts vary by brand and recipe, so always check the label of the exact product.