French fries

French fries rests on starch or a refined base, and starch is not a FODMAP - it is a polysaccharide, digested to glucose in the small intestine. What would change the answer is an added ingredient rather than the base: onion or garlic powder in the seasoning, or inulin added as fibre. The dependence on serving size comes from Gibson and Shepherd, who built this approach: what these carbohydrates do is deliver fermentable substrate and water to the end of the small intestine, so the quantity decides the distension. Their trial also found that restricting them GLOBALLY works where restricting them one at a time does not.

French fries are low because they are potato and oil, neither of which ferments. Baking and drying are the two processes that end the amine question rather than starting it - heat kills the bacteria and dryness stops the rest. A sourdough proved for two days is the counter-example.

Potatoes contain no gluten. Chips are a may-contain because of what happens around them: a shared fryer with breaded products, or a flour coating added for crispness. Frozen chips often carry both. What a label may promise is set by regulation and not by a recipe: 828/2014 allows "gluten-free" at or below 20 mg/kg, sets the conditions oats must meet, and admits wheat-derived ingredients in a gluten-free food provided the finished product stays under that ceiling. It measures nothing — it says what a food must meet to carry the claim, which is exactly what a food name cannot tell you.

Potatoes carry almost no fructose. Chips are on the scale because of the dextrose dip used to even out the colour during frying - and dextrose is glucose, which helps rather than hurts.

Potato carries no fructan, so plain fried potato is outside this axis. What puts a portion of fries at risk is the seasoning - onion or garlic powder in the coating - rather than anything in the potato itself.

French fries can carry a little sorbitol from the additives used to keep the colour even during frying. It is small, and it comes from the process rather than the potato.

Potatoes carry very little sucrose. Chips are on the scale because of the dextrose dip used to even out the frying colour - and dextrose is glucose, which needs no sucrase.

Peeled potato is the lowest thing there is in salicylate; skin-on fries are not. The frying oil and any seasoning are the other variables.

Chips are potato and oil, both low, fried in equipment that is metal. The measurable contribution in convenience foods comes from the processing line as much as from the ingredients.

French fries are peeled potato and oil: the skin, where a potato keeps its oxalate, is gone before the fryer, and the blanching water takes a little more. The oil adds nothing on this axis.