It is a complicated one.
I can't see keeping a normal HbA1c is going to stop Types 1, 1.5 or 3 developing.
And for T 2s, if your diabetes is caused by insulin resistance > weight gain > exceeding your personal fat threshold > liver dysfunction > T2, then losing weight is at least part of the answer, regardless of HbA1c. But if the insulin resistance is still there, the root cause is still there.
But there are many other causes of T2 (T2 is an umbrellas term for a lot of different mini-types).
For instance,
- a lot of older people develop T2 through age related deterioration of their organs.
- there are hereditary factors (i am the 3rd, maybe 4th generation to get T2 in my family, and it always hits at a certain age, regardless of weight, lifestyle or diet - assuming that domestic servants, businessmen and farmers eat somewhat differently!)
- also environmental factors.
Having said all that, maintaining a normal HbA1c will help tremendously in reducing risk of diabetic complications, both before and after diagnosis.