I watched this first-hand with our first box of Frosted Flakes. I took M with me shopping, something I try not to do, and she asked for frosted flakes. I had already said "no" to ding-dongs and a few other things (I much prefer Ghirardelli brownies anyway, which M also likes...) and I wanted to see what happened, so we bought a box.
We had the cereal on offer the next few mornings, and literally ALL M ate was dry frosted flakes. Nothing else. Not enough variety, not enough fat or protein to sustain her and our mornings were more difficult. I didn't explain that she needed to eat other things, but after 3 mornings of this, we said, she "could have toast, eggs or Kix or Oat Squares today." She chose the toast and some Oat Squares and milk and was fine. I expected a big battle for the FF's but didn't have it.
It was an interesting experiment. We might offer it on occasion, when she's home and I know I can offer a balanced snack or lunch, but it definitely confirmed the sweets-kill-variety if not managed appropriately.
What have you noticed with sugary foods?