A fat extender is any food additive or ingredient that allows the fat content of food to be reduced without affecting texture or flavour unduly — the technologist’s substitute for fat’s functional roles. Fat does many jobs — lubricating, aerating, carrying flavour, creating melt-in-the-mouth richness — so removing it collapses the product unless something stands in: starches and gums mimic its viscosity, microparticulated proteins mimic its creaminess, and water or air replace its bulk. Low-fat spreads, dressings, ice creams, and baked goods all depend on extenders. The challenge is honesty of eating quality — the reduced-fat product must still satisfy — and of labelling, since “light” has legal meaning. Fat extenders are formulation at its most demanding: rebuilding indulgence with a fraction of the fat.