NewfYork,
I'm a product design engineer for a med. device and med. implant mfger. Based on my experience with different materials and their biologic impact - I would say there's nothing good in plastic bowls that anyone should ever want to leach out into their dog's diet. HOWEVER, plastic bowls are typically inert and usually the plastic material itself is not always the cause of skin reactions, etc.... In fact people with sensitive skin and/or specific allergies sometimes need to use plastic razors over steel for shaving.
Regarding "Rubber".... I would guess your nutritionist actually means plastized rubber or most probably "Plastic" when they talk about what they're using. Because actual rubber is not a material that you (typically) want to make food bowls out of. Check out your tires on your car.....
To summarize; Stainless Steel bowls (specifically 18-8 SS) are probably the safest thing for your dog's health. BUT PLEASE , ANYONE WHO HAS PLASTIC BOWLS - Please don't feel like you need to throw them out.
The only thing I personally prefer about stainless steel is the fact that the material doesn't absorb food, germs, etc, hence it's easier (in my opinion) to keep sanitary.
I hope this helps a little.
Regards,
The Kureks
and their new Newf Pup (Angel)