Full-fat milk, cheese, or yoghurt still has all the fat that is naturally in it. The shop has not taken any of that fat out. You set it next to low-fat (some of the fat taken out) and skimmed or fat-free (almost none left). In British English, full-fat milk is the everyday name. In American English people more often say whole milk for the same kind of milk. On Taiwan cartons the label is 全脂. This is a food word. It does not describe a person’s body. Though actually, some speakers jokingly say “the full-fat version” to mean the complete version of a plan or a product, with nothing reduced. That is a stretch from the milk meaning; the home meaning is still milk, cheese, and the like.