True, insulin tolerance is seemingly irreversible. Better to stay off high carbs from a young age.
If you are diabetic, stay away as much as humanly possible.
There was a story on here a few months ago about a 600 cal/day diet that reversed diabetes in a few weeks.
Anecdotal story:
http://www.dailymail.co.uk/health/article-2385179/I-reversed-diabetes-just-11-days—going-starvation-diet.html