Is gum arabic a nut?

This question has a better pedigree than most label rumours, because the alarming detail is in the regulation itself.

The detail

The US regulation describes Gum arabic as the dried gummy exudate from the stems and branches of trees of the genus Acacia, family Leguminosae.

Leguminosae is the legume family. Peanuts are legumes. So a reader who looks up the regulation finds gum arabic filed next to the most feared allergen on the list, and draws the obvious conclusion.

Why the conclusion does not follow

Two things are being confused: how botanists group plants, and what an immune system reacts to.

Botanical families are grouped by flowers, fruit and seed structure. Acacia and peanut share a family the way a lemon and a kumquat do, which tells you about pods and not about proteins.

An allergy is a response to particular proteins. Peanut allergy is a reaction to specific peanut seed proteins. Gum arabic is not a seed at all: it is hardened sap from the trunk and branches, and it is mostly complex carbohydrate.

Relatedness in a family sometimes does predict cross-reactivity, which is why the question deserves a real answer rather than a dismissal. It does not do so automatically, and it does not do so here.

What the law says, which is the shorter version

Acacia does not appear on the US list of major food allergens, and it does not appear on the EU list of substances that must be emphasised in an ingredient list either. Both lists are the product of review rather than habit.

That means no declaration is required and none appears. The mechanics of how those declarations work, when they do, are on the page for people reading labels for an allergy.