Remember, the primary diabetic problem is control of glucose levels. Sugar, from whatever sources, is turned into glucose in the liver ~ just like we were big ol' bumble bees!
I've been working at this for half a decade and I think I've gotten my daily swings down to about 110 points ~ can't imagine an "average" of 100.
I described myself earlier. Five years ago, after 3 years of progressive loss of feeling in my feet and legs, but NORMAL fasting glucose levels, my Dr found that my A1c was nearly 8. He handed me a copy of a diabetic diet, and a prescription for a meter. I was supposed to just measure glucose twice a day to establish a baseline. The following evening I had the featured dish at a chinese restaurant - sweet & sour something, over a heaping mound of rice - and a glucose reading of 244 two hours after the meeting!
So I did some research, and decided that the diabetic diet was filled with carbohydrates - and I would be better served with a low-glycemic diet - and it has CONTROLLED my glucose for 5 years, with NO medications for diabetes. My A1c is normal, and my glucose (2-4 hours after eating) is normal as well. But the neuropathy (confirmed by nerve conduction tests - persists, although it has stopped getting worse.
According to some, I am not diabetic like my mother was, but I know that sugar, (including orange juice or soft drinks,) rice, or potatoes in any quantity will send my glucose above 200 again, and pasta or bread are almost as bad. I suppose that would be the hundred-point swing you describe - but I don’t do those things any more.