I think you would be hard pressed to find any studies as it would be pet food companies that fund the studies and they don't want people to start feeding their pets quality, human grade, the way nature intended food.
The concentrated protein levels in kibble along with the chemicals could really do a number on some animals, just like junk food full of carbs and sugar are affecting children.
Cat maid to:
Jasper, male Ragdoll ?? (approx 10 yrs)
Rose semi feral, a cpietra rescue, female tabby (approx 7 yrs)
Sweet Pea RIP (2004?-2014)
Puddles RIP (1996-2014)
Snowball RIP (1991-2005)
In a cat's eye, all things belong to cats.-English Proverb
“While we are free to choose our actions, we are not free to choose the consequences of our actions.” Stephen R. Covey