Whey

Whey is the liquid the lactose leaves in when milk curdles, so drying it concentrates the milk sugar instead of removing it. This is also why the cheeses that drain the most whey end up the lowest in lactose.

Whey is the liquid the lactose left in when the curd was drained - so it holds what the cheese gave up. It is where ricotta comes from, and it is the reason a cheese and its by-product sit on opposite sides of this axis.

Whey is low because it is the watery fraction left when curd is drained, and amines stay with the protein rather than the water. Histamine in dairy is a storage measurement, not a recipe one. Milk is not a fermented food, so its histamine depends on how it was kept rather than on how it was made - and that is exactly what the study behind this level varied: STORAGE CONDITION. A dairy product's place on this axis is a question about the cold chain.

Whey holds what the curd let go, and that includes the milk's small oligosaccharide fraction along with the lactose. The fraction is small and the lactose is not, which is why whey is moderate on the FODMAP axis and low on this one.

Whey carries no gluten, and it holds an odd place in the evidence about gluten: it was the control. Biesiekierski's double-blind cross-over gave 37 people with self-reported gluten sensitivity either 16 grams of gluten a day, 2 grams plus whey, or whey alone, after two weeks of reduced FODMAPs — and no gluten-specific effect survived the FODMAP reduction. Whey was the thing the gluten was measured against.