Categories in a supermarket look natural and are not. Each one exists because a set of products could be made, described and shelved together, and the low-fat aisle is a good case because all three parts of that sentence changed at once.
The manufacturing side came first. Removing fat from a familiar product changes its texture, its behaviour in cooking and its shelf life, so the category depended on solving a set of technical problems.
Reformulation is a technical problem
Fat carries flavour, provides mouthfeel and does structural work. Take it out and something has to do those jobs, which is why reformulated products typically have longer ingredient lists than the originals they replaced.
That is a description of food technology rather than a criticism. A product engineered to a specification will show the engineering in its ingredient list, and the list is the honest record of it.
Labelling made the category visible
A category needs a claim a shopper can see from a distance. Rules governing descriptors gave manufacturers a defined vocabulary and shoppers a consistent one, and the aisle became legible as soon as the words were standardised.
The definitions are technical: they specify thresholds against a reference quantity. Read that way, the claims on the front of a package are compact and precise; read as general recommendations, they were always going to mislead.
The aisle as a historical document
Walking a supermarket aisle is a way of reading the recent past. The categories on the shelves record what was manufacturable, what was sayable under the labelling rules of the period, and what shoppers were understood to be looking for.
Categories are also unusually durable. Shelving arrangements outlive the arguments that produced them, which is why an aisle can go on describing a conversation that has largely moved on.