Over-Treating Dog

I have a friend who loves his Parsons Terrier more than life itself. He throws dog treats to him constantly. For example, during our dinner time, the dog will have gotten 5 treats within that time. The dog is as fat and round, like a bulldog and will not walk more than a couple blocks. He also is only fed canned food, when it's his actual dinner time. How do I tell my friend that he is the cause for his dog's weight and for him to understand this is not ok and actually making the dog have less of a life? He is the type that will be easily offended about things, especially when it comes to raising the love of his life so I want to make sure I'm sensitive to this. I also feel FACTS would be good to present to him and can not find too much detailed information on this on the internet so if you can point out a website or a good book, please let me know. I need him to understand how many treats is too much and what issues an overweight dog will have.

Has the dog been to the vet's recently? The vet should have given him what-for for the condition of his dog.
   
People who do this drive me nuts.
   
Ask him if he'd like to have a crippled dog who can barely walk with diabetes in a couple of years. A statement like that may get his attention.
   
Websites for factual stuff:
   
http://www.puplistings.com/dog-articles/consequences-of-fat-dogs.html
   
("Fat Dogs - Consequences of Your Dog Being Overweight")
   
http://www.doggienews.com/lib/health/fat-dogs.htm
   
("Taking Care of a Fat Dog")
   
http://www.veterinariancare.us/pet-care-article5.php ("Why Obesity Matters")
   
SEARCH TERMS: dog health overweight OR fat

Fantastic links! Thanks for your help! Yes, I believe he's been to the vet before, but I'm not too sure how much emphasis the vet put on the condition, since I've known vets to be a little too gentle sometimes and not state the urgency. I'll see about trying to get these links over to him somehow without offending him! Thanks again!