9 y/o female Min-Pin

This is my boyfriend's dog. She experienced a back injury about a month ago and I know it was likely a result of her weight. When she went to the vet after the injury, she weighed in at 20 pounds! Personally, I typically have large breeds as companions, so I'm guilty of distributing treats, but for the past year I've been trying to limit how much he treats her because she quite obviously overweight and I don't think the people food helps. Despite her injury, though, he continues to give her everything from pizza and wings straps to wet dog food servings to legitimate dog treats, on top of near 2 cups dry food a day.
Advice to help him see how severely damaging this is to her health? I hate knowing her life is being cut short. ): Her gray hair shows it, enough.
Thanks for any input.

[ginger899]

Well, all I can say is what you already know.
This is WAY too much food. Unhealthy, and will almost definitely shorten her life and make the later part of her life disease-ridden and painful.
This is not kind, it is dangerous.

There is no harm in giving her a very small amount of fish or chicken (plain boiled with no seasonings) to add with her dried kibble...but she should be on two meals a day -breakfast and dinner, or three very small meals (depending on how early she gets breakfast) And NO treats. Her weight HAS to come down.
This may sound boring. But it would be a kindness.
Make sure her dried kibble is a very good quality one (no fillers, no "nasty" unhealthy or unnecessary ingredients) so she is getting tip-top nutrition.
Then read the amount she should be fed each day according to the weight she OUGHT to be (I'm sorry but I don't know the weight a Min Pin should be, as I've never had one)
She is also going to need daily regular decent exercise, (ask your vet for guidance about this, as she has just had a back injury) But at least she should have gentle walks if the vet agrees.

Make sure she has access to plenty of fresh water, if she is on dry food.

[ginger899]

P.S.
Many dogs have a way of wolfing down what they are given to eat, then looking for more -as if to say "what? Is that all I get? I could eat WAY more!"
This can seem like they are still hungry, and many people waver when they see a dog do this, and think they haven't had enough to eat, so feed scraps, or more food.
But I have not known a dog yet who wasn't an opportunist when it came to food. Please be strict. Give her the measured out meals, according to her needs, and don't be taken in by those "looks" she may give you. Withholding those treats is not being cruel!

[Jaybay]

Not only does that extra weight make any injury worse, it can cause the same kinds of problems that happen in overweight humans like high blood pressure, diabetes, and congestive heart failure.  My mother-in-law killed her chihuahua doing exactly the same thing your boyfriend is doing to his dog.  The fat-laden human food also makes her a ticking time bomb for pancreatitis, and that's not something I would wish on my worst enemy. It's extremely painful and the end result is usually death.  Even if she survived a bout of acute pancreatitis, she could end up with chronic pancreatitis and on an extreme lowfat diet for the rest of her life.  For the poor dog's sake, I hope your boyfriend wakes up to reality before my mother-in-law did.  Best of luck to you both.