From what I read, a while ago, it was a physical/mechanical problem rather than a chemical one. I know this is why crickets tend to die if fed a lot of repcal. The calcium powder binds up in their digestive system, making their gut contents set up like concrete.
Chameleons get much o ftheir calcium from the gut contents of their prey. Many chameleons eat a ton of grasshoppers, which feed primarily on high-calcium grasses.
Gutloading can present a problem: In th ewild, chameleons have to eat substantially more to maintain weight. Parasites, and insects with significantly lower nutrient-density means a larger volume of insect gut content is ingested per day than in captivity.
We feed our chameleons insects that are far more nutritious than they'd get in the wild normally - ground dwelling crickets, beetle larva, moth larva, roaches, etc. In th ewild, much of their diet is high in chitin, and much lower in fat - adult betles and flying insects, flies, etc.
They get a lot more fat and calories out of an equal mass of insects in captivity than in the wild.
So, in captivity, we've got fat lizards that are getting less gut content in their meals. It is a major reason for nutritional imbalances in captivity, I believe.
This is purely hypothetical:
Think about how much grass is consumed by the average grasshopper. It's substantial. Then factor in the high chitin content, and relativly low meat/fat content(compared to a grub), of your average adult grasshopper. The chameleon might have to eat 2 large grasshoppers to equal the calories of one big superworm, yet the gut content in those two grasshoppers is probably many times more than that of the superworm. On top of that, it's low-calorie grass that has a lot of calcium and D3 in it.
think of the long-term effects of this.
It's why I feed my insects mostly greens!
also, I'd avoid feeding dog/cat/fish food to crickets, unless you're growing them up. Don't use it as a gutload though. Chameleons can get gout if they consume too much animal protein. Meat is easy for them to digest, but their body doesnt' deal with it very well over time. Nearly every instance of gout I've seen in chameleons has been a result of people feeding their crickets doog food or fish flakes as a gutload.