Hum I hadn't heard this one before. I think there is a genetic componet to it since we tend to see them more frequently in certain breeds, ie labs, shelties schanazers. It is interesting that it might be diet related. I'll have to ask about diet in dogs I see develop them.
My personal experience: my Lab had tons of them, she was fed the gambit of dog food garbage. Cheaper the better, I was a poor student and didn't know better. Last years of life ate eukanuba.
My Jrt mix-food allergies to beef, don't know what she was fed the first year of her life, ate Cal natural, Innova and RC MP and LP. 1 small fatty lump never bigger than 1in diameter.
My dad's Lab- tons of fatty lumps fed some type of high grain diet Chuckwagon? talked into Iams , now on Innova(yah)
My brother Lab- fed Innova since baby puppy-no fatty lumps
My breeders shelties- no known Fatty lumps- ate eukanbua and RC
My shelties-no fatty lumps so far- Ate eukanbua(Justice) and then Eagle pack Holistic select and Nature's variety.
Interestingly the 2 with the poorest diets had the most but they were also obese. None of the others were/are. But the high grain diets is something to watch.