Hi sabnat.
Has your husband been diagnosed as a Diabetic (Type) or just told that he needs to be careful to stop diabetes later on ? Pre-Diabetic in other words. A proper diagnosis would have involved more than one test usually.
Testing his Bg levelks is good, but you need to be more specific about when you are testing. A reading of 5 - 6 first thing in the morning is good, but what are the readings 2 hrs after meals ? They are very important.
Diet can work well for a lot of people. It does all depend on those Bg levels I mentioned above though as to whether it is controlled or not ?
Further advice from your GP/Nurse is required.