But in US, all the food has an indicator of how many grams of carbs, fat and protein in each serving. So he should have no problem.
If he feels bit low blood sugar during the day, he would himself notice it because he might feel dizzle and then he can get a quick drink of apple juice, which would make blood sugar back to normal.
Type II DB is more studied in life science but it is harder to control the blood sugar level from the abnormal metabolic level.
No worries about his Type I. If you are really concerned, ask him if he might develop any "眼疾". That is because of bad control of his blood sugar when he was young. If he is fine, you should have no worries.