"lab animals being fed controlled diets are now getting fat, as are feral animal colonies" What does "now" refer to here? I imagine in the case of the human po

"lab animals being fed controlled diets are now getting fat, as are feral animal colonies" What does "now" refer to here? I imagine in the case of the human population's growing obesity, the "now" means contemporary western diet. If this weren't lab rats, I guess I would assume you mean street rats eating trash produced from contemporary western diet is leading them to get fat. But these are lab animals and the diet is "controlled".