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Diet and exercise will definitely help in preventing pre diabetes
to frank diabetes. Your weight should be in accordance to your height. Suppose lets say your height is 156 cm the your ideal weight would be 50 to 56 kg (156-100). There is no chance that you wont develop diabetes, You will , eventually, but with these you can prolong the time period from now to when you would actually turn into a diabetic.
Hope this answers your query.