Can't tell you why the levels were high on the all carnivore days unless there was something in the carnivore diet that was high in sugar. Liquid milk would be a good example. Milk (lactose) would spike my blood glucose levels about as bad as any food. Milk is from an animal so it would be carnivore, but it sure is not low in carbohydrates. There is a difference. Ice cream would be from an animal source so carnivore, (edit: ok I'm wrong on that because there is sugar in ice cream which is a plant material) but it will sure spike blood glucose. Eating carnivore is not automatically low carb. You have to eliminate the high carb animal foods to be low carb to avoid spiking blood glucose and resulting high insulin levels.

When you test can make all the difference in the world. Was the test fasted (not eating for a time) or after a meal (post prandial)? For a non-diabetic in the morning before any food is ingested a sub 100 fasted reading would be optimal. A diabetic should be under 130, preferably considerably under. An hour or so after a meal a non-diabetic would be optimal under about 140. Also good for a diabetic but under 160 is generally accepted as ok. You didn't say the details of the test about when they were taken (in relation to when the food was eaten), so not so much can be determined.

When eating a high carb meal (pizza with the bread crust and sweet sauce) the highest reading will be about an hour after the meal. If your pancreas is working properly it will provide adequate insulin to bring the blood sugar back down. Lets say it spiked to 200 an hour after the meal. At three hours after the meal it could be back below 100 (because of the work of insulin from the pancreas). There is sometimes a rebound effect where the blood sugar goes low (maybe down to 60-70) and this will produce a hunger signal urging you to eat again. That is the problem with sugar and carbs in general. They are a fast energy source, cause a big spike in insulin to take care of it, then the insulin sometimes over shoots and blood sugar goes a little low bringing on hunger for the cycle to start all over. Why low carb works has a lot to do with satiety and hunger control.

If you really want to see what is gong on with blood glucose levels based on what food you eat, get a continuous blood glucose monitor. I have heard doctors may be able to prescribe one and get one to try for free for 30 days, but I have no personal experience.

It all depends on when you took the blood glucose test in relation to when and what you last ate. A good routine to get into would be this. Test your blood glucose soon after you get up in the morning but before you eat or drink anything. Then also test it about an hour after every meal if possible or at least an hour after supper if only going to test once in the evening. The morning (fasted) reading should be around 100ish and the one hour after meal (post prandial) should be under around 140 if you are not diabetic. Anything significantly above those levels would be an area of concern.

If you want to see what foods spike your blood sugar, eat them then check your blood sugar an hour after eating. That will be the highest reading from that food. A non-diabetic will then fairly rapidly start dropping (insulin doing its job) whereas a diabetic might have lingering high glucose levels still at two hours after the food ingestion (because of insulin resistance that has developed over time because of excessive insulin in their system).