A note for any recently diagnosed Type 2 diabetics that may lurk here:
As someone beginning the whole Type 2 odyssey as I age (family genetics) and try to shed the lifetime of extra weight gained through the insulin resistance plaguing many of us... I find measuring and keeping track of blood glucose levels to be very motivational and comforting. Yes the poke sucks but get it over with quickly and it just becomes a very brief of waking up in the morning.
Collecting morning fasting and an occasional 1h and 2h after meal makes for amazing data. I'm a bit of an analytical nerd and find having the data to be comforting. It makes decisions easy. With a single daily poke with the number written into a log I can point to proof that keto is beneficial to my health. I can already tell that 4 months into the keto diet that it is not a "diet" but a lifestyle change that will let me avoid taking any medications for T2DM for hopefully many years. Every morning I get a self diagnostic check on how things are going.
As a bonus tracking your morning fasting seems to also warn you of when you're about to get a cold. I've found that morning fast sugar pops 20 to 30 points higher than normal the day before the symptoms start for a cold. That's my cue to get some more sleep.
And getting an A1C blood test is another great source of data. I reverted back to dead center normal blood sugar in only three months of keto. The A1C test makes it hard to lie to yourself about your diet due to it functioning as a quasi-average across a period of time.
All of this data makes it hard to lie to ones self about what one can and shouldn't eat. I can tell with as much certainty that one can have in this life that the keto diet has done wonders for my blood sugar levels to the point where I don't need any medications. Simply dropping daily net carbs under 30g has reversed the symptoms of a metabolic disorder. And I've lost 30 pounds without any significant increase in physical activity and little real effort at restricting total calories.
As for the donut I've already confirmed with testing that eating a donut is not worth it. When experimenting with a "new" food I will sometimes take a reading one hour or two hours after eating the mean containing the food and I'll get my answer. If 1 hour is over 140 or 2 hour is over 120 it goes on my "body can't handle it" list. Broccoli and such don't trigger this. Potatoes? Oh yeah, never again. I can't go "oh, maybe that's fine....". Nope, I have concrete data saying not to do it.
The insulin restriction theory of keto works incredibly well for diabetics.