Konjac

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

Yes — Konjac is high in FODMAPs. Konjac is glucomannan, a fibre that absorbs many times its weight in water - which is what makes it a thickener and a diet product at the same time. That swelling happens in the gut, and the bacteria ferment what is left. It is the clearest case among the FODMAPs of a fibre that helps and troubles by the same mechanism. The criterion is fermentability rather than chain length, and that is Gibson and Shepherd's definition: a long chain that ferments slowly is not the problem; a short one that ferments fast in the proximal colon is.

Yes — Konjac is high in oligosaccharides. Konjac is glucomannan, and it is used precisely because it is not digested: it swells in water and is sold for satiety. What human enzymes leave alone, colonic bacteria ferment - and it is that fermentation, not the chain length, that puts glucomannan with the oligosaccharides.

Konjac contains only low levels of nickel. Konjac is milled from a tuber, and a tuber sits in the soil for a season absorbing what is there. The flour is nearly pure glucomannan fibre, and it carries little of that nickel through.

Konjac contains only low levels of oxalates. Konjac is a milled tuber, used as a thickener at fractions of a percent. Whatever oxalate the source plant held, the amount reaching a portion is too small to register. Amounts vary by brand and recipe, so always check the label of the exact product.