Flavia,
I live in Uruguay, we also have large populations of T. merianae.
I keep and breed them, and I dont think giving them pet food from time to time is bad.
When you look at how they live both in the wild and in suburban areas, they are feeding on ANYTHING they find.
And they FLOURISH!!!

These lizards are adapted to being flexible in their diet.
My friend, the late Bert Langerwerf, gave them even human food like cakes.

As a matter of fact, my mother in law told me about picknicking and a tegu stealing the food! Tht is not unusual in the least.

I dont know about Brasil, but since they are considered chicken coop raiders in Uruguay and are killed to protect egg production, some keepers feed them just eggs, and then you get huge fat and unhealthy lizards

If the species itself is flexible, why shouldnt we, too?

David