I was not able to eat any cereals without spiking my blood sugar significantly back when I was overweight, but now that I have lost a huge amount of weight, I find that I can occasionally eat a bowl of rye cereal, certainly not every day r even every week, and I only sweeten it with stevia. Rye is much lower on the G.I. than wheat, barley, or oats. My favorite is cracked rye (very tasty and lots of fiber), but rolled rye (just like oatmeal but made out of rye instead) is quite tasty, too. Unfortunately, I can't currently find rolled rye, nor cracked rye in my local stores. I have to order it online.
I've found the same thing with bread. I can occasionally eat a slice of 100% whole rye bread, without significantly spiking my blood sugar. This the kind of bread that has no wheat at all in it, and no added sugar. It's a very dense, dark bread. I sometimes will eat it with fried eggs, to soak up the runny yolks. And I limit myself to one slice. I think its called "whole rye bread" and it is made in Germany, but I have been able to find it way over here in Oregon at various stores. Mestemacher or something like that, I think, is who makes it.