Mannitol

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

Mannitol contains moderate levels of FODMAPs. Mannitol is the polyol of mushrooms, cauliflower and celery rather than of sweets - which is why those three vegetables are on this axis at all. It is absorbed slightly better than sorbitol, which is the whole reason it sits a level below it.

Mannitol contains moderate levels of sorbitol. Mannitol is the polyol of mushrooms and of some sugar-free products. It shares sorbitol's mechanism but is absorbed a little better, which is why it sits a level lower here.

Mannitol contains only low levels of nickel. Mannitol carries a trace of nickel for a reason written into the law that governs it. E 421 is made by CATALYTIC HYDROGENATION and the catalyst is nickel - the regulation says so in its own text - so its purity criteria carry a nickel limit of 2 mg/kg. That is a legal CEILING and not a content: what a given batch actually holds is not published, and 2 mg/kg is an order of magnitude below the foods that lead this axis. But a ceiling exists because a trace is expected. Amounts vary by brand and recipe, so always check the label of the exact product.