Any food that is a seed mix is probably not the best thing for a rat. Even though they may say they are formulated for rats and mice, they often contain items much too high in protein and often things rats don't eat at all...like rabbit pellets. They simply put it in to fill out their product without any regard for what is actually healthy for a rat.
A lab block is a condensed, cylindrical "chunk" of food, that's specially balanced to contain all the nutrients and such that a rat needs.
Some brands are...Teklab, Harlakan, and Kaytee. My boys seem to like Kaytee the best, and it's easily available in most American pet shops.
Since lab blocks are never really a huge hit, I add other yummier health food to their diet, like veggies and homemade seed/grain mixes.
Good luck in finding a lab block, it shouldn't be too hard, they're very common.
