I think the core of the Slimming World plan is very "pure" in terms of the foods
I'm really impressed the by way that new and different foods are encouraged e.g.
Cutting edge veg
fabulous fruit
and the use of things like cous cous, quinoa and qourn - which most of us would never have tried pre-SW mean that even after the active phase of weightloss, most people's diet will be slightly different post SW
you can easily follow the plan and not eat the processed foods like cheese triangles, sweetener drinks or yoghurts
I like the ideas that Michael Pollan has - about avoiding food products containing ingredients that no ordinary human would keep in the pantry or that a third-grader cannot pronounce, avoiding heavily processed foods—which he calls “edible foodlike substances.”
I'm not very successful at keeping to his rules, - but they make a good rule of thumb!
Eat food, mostly plants, not too much