I misunderstood when I heard about this story, or the person telling me about it did. It speaks of a diet, and of course that usually means a temporary change in food regimen, but in this case, the reference to diet is about clothing.
The way it was explained to me, people who'd lost weight had chosen to stick with six garments only until their weight had stabilized, so that they didn't end up with a range of sizes for the long run.
I see now that this makes no sense, but what it recalled for me were the days when I was dropping from 365 to about 200, where I remain today 20 years later. Except for a couple of size 64 sweatpants that I bought (slightly oversized for what I needed) — while I was in rehab, I got rid of every stitch I owned, and eventually disposed of everything I'd bought to replace it on the way down, because that stuff no longer fit, either.