Why ninety per cent fat free beats ten per cent fat

Ninety per cent lean and ten per cent fat are arithmetically identical. Given one or the other, people rate the leaner-sounding version as higher quality, better tasting and less greasy — and they do so before tasting anything, then again after tasting the very same product.

What everyone sees

The wording looks cosmetic. Anyone who can subtract ten from a hundred is assumed to be immune, and a preference for the positive phrasing is put down to mild pleasantness with no consequence for the decision that follows it.

What is actually happening

Attribute framing works by directing attention to one end of a scale, and the named end is the one encoded. The lean version makes leanness the topic; the fat version makes fat the topic; each becomes the axis on which the product is filed. Measured effects persisted after direct experience of the product, which is the part that separates framing from mere phrasing.

Why it stays hidden

It escapes notice because the arithmetic is trivially reversible and therefore assumed to have been reversed. Nobody experiences the moment of not converting, so the reader remembers having evaluated a fact rather than a wording. Sellers face no obstacle either: both statements are true, so there is nothing for a regulator to correct.