Hi,
How long ago did you switch from canned to dry food?
Lynn
That is a large weight gain for 1 years time, and yes, being overweight is a health risk. It makes it way more likely for the cat to develop diseases such as diabetes and heart disease. Here is a link to a page that shows how to tell if your cat is overweight:
http://www.placervillevet.com/feline%20body%20condition.htm
I would recommend feeding him less. A 10# cat only needs about 1/4 to 1/3 cup of food twice daily. I would cut him back to a total of 2/3 cup per day, and then check his weight in about 3 weeks. If he hasn't lost any, cut back to a 1/2 cup per day. If he has lost, continue to monitor his weight until he gets to where he should be. Dry cat food tends to contribute to obesity. It would probably help to switch him to canned or at least substitute part of his diet for canned. Here is a link to a page about this:
http://www.catinfo.org/#Common_Feline_Health_Problems_and_Their_Ties_to_Diet_
If you have further questions let me know. If this answers your question please click accept. Thank you.
Veterinary Assistant
worked at a vet clinic for 15 yrs, BA in biology, have had cats most of my life