He should be staying away from all carbohydrates including whole wheat bread and his diet should be fat and protein. You're hypoglycemic because of the drugs. If he's not yet on any drugs, and completely cuts out carbs, his glucose level would stabilize back to normal.
It's a tough diet tho. I managed for 2 days only. Couldn't stand the constant hunger. But for him, unfortunately, it's either that or drugs/insulin for the rest of his life. There a good side to this diet: he would lose weight without even trying - that's certain.
You should be staying away from sugar, white bread, potatoes and etc. Your diet should be high in fibre and breads should be whole wheat. I am diabetic and have cut out so much carbohydrates that many times I am hypoglycemic.
Good luck.
What exactly do you mean by "eat healthy" in your particular case?
Carbohydrates get converted by the body into glucose and raise the blood sugar level, which in turn triggers the release of insulin.