Grapefruit

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

Grapefruit contains moderate levels of histamine. Grapefruit is a liberator like the rest of the citrus group, and it has a second property worth knowing that has nothing to do with histamine: it inhibits the enzymes that clear many medicines, which is why so many drug labels warn against it. Two different interactions, one fruit. 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.

Grapefruit contains moderate levels of tyramine. Citrus was on the original MAOI diet and came off it decades ago - grapefruit's measured tyramine is too low to matter. Its famous drug interaction is real and entirely separate: it inhibits the enzymes that clear many medicines, which has nothing to do with amines.

Grapefruit contains only low levels of sucrose. Grapefruit carries its sugar mostly as free glucose and fructose rather than as sucrose, so there is little for sucrase to split. Sweetness and sucrose content are not the same measurement, and this fruit is the proof.

Grapefruit contains only low levels of FODMAPs. Grapefruit carries most of its sugar as sucrose, which splits into glucose and fructose in equal parts - so the glucose escorts the fructose across and nothing is left over. Citrus is the reliable fruit on this axis, and the juice is lower than the fruit only because the pith goes. Amounts vary by brand and recipe, so always check the label of the exact product.