Maltodextrin. It’s in many things. It’s in a lot of things marketed as “safe for diabetics”, and THAT should be criminal. Maltodextrin has about twice the glycemic index as table sugar.
I kept having really high BG tests, not really high, but in the 120’s to 140’s. That’s eating ZERO CARBS for weeks, so wtf? Why was my BG so high all the time. One of my staples at the time was Metamucil. I figured a fiber supplement wouldn’t hurt. It was the sugar free version. It tasted enough like orange juice to scratch that itch, and I was drinking it several times a day. After checking with my doctor of course who said “yeah, that’s fine”. 
Turns out it has maltodextrin in it. A lot of powdery or grainy products use it to prevent caking. Iodized salt has it to. I don’t know how much maltodextrin is in either of those two products, but I stopped using them and the next day my BG levels were staying in the 80’s instead of 120+ range.