Oyster

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

Yes — oyster is high in nickel. Oysters filter enormous volumes of seawater and keep what they filter, trace metals included. That is the same mechanism that makes them high in zinc, working on a metal nobody wants. The second French Total Diet Study ranks the food groups for nickel rather than valuing them, and tofu heads that ranking.

Oyster contains only low levels of histamine. Oysters are low in histamine when alive and cold, which is how they are sold - but shellfish are also classic histamine liberators, releasing the body's own stores without carrying much themselves. That is a different mechanism and this level does not cover it. The Swiss list rates it 2 of 3 under “oysters” and marks it H! for rapid histamine formation and L for liberators of mast cell mediators. The letters are a presumed reason, not a measurement. Amounts vary by brand and recipe, so always check the label of the exact product.