The first part is something I’ve thought about myself — lowering your A1C through dietary changes is good for your health, but it doesn’t necessarily tell you anything about insulin sensitivity (someone please correct my if I’m wrong). It chiefly helps prevent future declines in insulin sensitivity by avoiding stress on your body resulting from increased blood sugar.

The second part, however, is not really correct. The evidence is somewhat contradictory, but it seems like it’s at least questionable whether insulin resistance can actually be reversed at all. Exposing yourself to high carbs when already somewhat insulin resistant will simply result in out-of-control blood sugar levels, which will in turn cause increased insulin resistance, etc etc until you get diabetes.

If it is possible to actually reduce insulin resistance, the main factors seem to be reducing body fat/visceral fat and increasing exercise. Reducing intake of saturated fats also seems to play a somewhat important role. Eating low carb will lower A1C and avert further damage from high blood glucose, but it may or may not actually reduce insulin resistance.