Hi Paul, there have been a number of different studies looking at whether type 1 (juvenile onset) diabetes can be prevented. Most of this research has been done in those at highest risk of type 1 diabetes, that is, people with relatives with type 1 diabetes and those who have early signs that they may be developing type 1 diabetes.
The main areas of research have looked at the prevention of type 1 diabetes using immuno-suppressive medications, oral insulin, intranasal insulin and injectable insulin to try and delay or stop the insulin producing cells being damaged. You can find more information on this research in Australia at the Walter and Eliza Hall Institute web site listed below.
Other studies have looked at diet, for example cows milk protein and gluten, however nothing has been proven to prevent type 1 diabetes to date. There is an international study at the moment looking once more into cows milk protein and the possible link with type 1 diabetes, check out the link below for more information.
Walter and Eliza Hall
diabeteskidsandteens - TRIGR