@carbcounter There's Glycemic Index (GI) — how quickly a food converts to glucose — and Glycemic Load (GL) — how much sugar you're likely to get from a typical serving.

Cheerios have a high GI (it converts to sugar quickly) but only a medium GL for a single-cup serving (because it's mostly air). If you have a more-typical 2-cup cereal bowl, however, then you're into the high GL range as well.

I realise it's counter-intuitive because Cheerios don't taste sweet, but the oats are so heavily ground up and processed that they convert to sugar almost immediately.