When someone "eats less", insulin sensitivity also improves, in theory. But the catch is that situation represents a vicious cycle: if you just eat less, you also get less nutrients, and it may be not sustainable if you eat highly-processed foods lacking the nutrients in the first place.

So a better idea is to eat less + consume more vitamins + consume more natural foods (to get those vitamins). Junk food + metformin combo works to some degree but in the long run it is more like a hack than a proper fix IMHO.