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For type 1 no because no matter what you do you need insulin and it is potentially dangerous if someone is suggesting that. The best you can hope for in type 1 is that you might reduce your insulin requirements by reducing your sugar intake.

For type 2 you can certainly reduce the severity with lifestyle changes as in most cases of type 2 they are producing enough insulin and the problem is due to reduced sensitivity. This can be altered by diet and exercise.