If he's fasting for a blood sugar test in the morning he should have specific instructions. If he is not fasting for a blood test in the morning I'd feed him.
As for the rest of the time, if you're still trying to find out if he has blood sugar issues, I'd make sure he eats a small meal at least every 3 hours. If he is diabetic he needs a consistent diet of healthy foods.
Please don't mistake my term, healthy foods, for salad and a vegetarian diet. I'm not saying that in any way. If he doesn't like the food he won't eat it and then he'll be worse off.
So you have to find foods he will eat and that won't push his blood sugar around too much. Eating a lower carb diet is often a good way to keep his blood sugar more stable too. BUT please make sure you do your own research.
Every "professional" will tell you a different story and say the same foods the other one said are bad, they'll say they're the only ones he can eat.
I like to give the kids a high protein snack when they come in from school. It tides them over until dinner. I don't do a lot of carbs but I did research on foods and carbs so I'd be sure what I was doing was good.
I also do NOT ever do any sugar free at all. They all say "It's good to use, it's not a bad chemical or it's natural" but over the long term there is always something wrong with them that hurt the people who eats them.
So we only use real sugar and real butter. I don't do fat free either. I got diarrhea for a week when I went fat free on some foods. I think that Gar Gum or something like that just slides through our bodies like slime and comes out the same way....
If he has blood sugar issues either way his diet will be crucial in the treatment of it. Please do your own research and decide what fits your family best. Listening to other people who don't know you and your lifestyle will only make this more frustrating for you.