Hello katywren and welcome to the forum.
I was told I was pre-diabetic 6 months ago and have been following a low carb diet. Previously I had tried to eat the same amount of carbs pre diagnosis, although 'better' wholegrain type carbs, but it did not really make a difference.
What I do, and would advise your husband to do if he can, is to get a glucose monitor and test his blood sugars after food. By doing this he can see how much carb and what type of carb he can eat without causing his blood sugar levels to increase. This is a long process, I'm still doing it now, but after a few months he will know what and how much he can eat. For example, I know I can have half a cup of brown rice with a chicken and veg curry or 1/3 cup of white rice and my blood sugar levels will be in the range I want them to be.
Also, exercising after a meal really helps decrease blood sugar levels. For me, a 15 mins walk 30-60 mins after eating can bring my sugar levels down when I eat more carbs than usual at a meal.
Of course, this advice is based on my own experience and your husband will need to find what works well for him. I think the way to go is low carbs and lots of exercise, but you have to find what works well for you.