A change in diet is the best way to prevent or slow the onset of diabetes in those who are predisposed to it. This entails consuming carbohydrates with a low glycemic index so that less sugar is stored in the bloodstream. This, of course, will not help those who already have diabetes, though it will help keep blood sugar levels under reasonable control – this does not mean you will be able to stop taking your medication, as this is dependent on your personal case history and your doctor's recommendations.