Possibly, but they weren't really testing to learn about the effects of old vs new foods in general. It's more a test of whether "metabolic junk" is significant

Possibly, but they weren't really testing to learn about the effects of old vs new foods in general. It's more a test of whether "metabolic junk" is significant to aging, so they used food sources that would have more or less of those factors present. The relevant compounds are different and not precisely known for the different organisms, thus the cannibalistic diets.