Green beans will bulk things up slightly (proportional to the amount you give) but nothing runny should result.
I give Tinker half green beans and half canned dog food (EVO 95% meat) with her morning meal, and in the evening just some green beans when the puppy gets her dinner. Hally gets the evening green beans, but not the morning. Puppy gets more food proportionally, so she doesn't get the green beans. I didn't put Tink on them to get weight off, rather to keep her trim without her being so miserable. She's got the luxating patella issue, so no extra weight can be allowed on her tiny frame. And she may look like a chi, but her stomach is clearly lab. She'd eat twice her weight every day if she could. She is MUCH more satisfied since she's getting the veggies. I so do not miss the days of her constantly haunting the kitchen, eating bits of whatever (often not food) in corners around the house, always hungry.
They'll eat most anything but spinach, (plain at least, I'm sure they'd eat that mixed with food) but green beans are the most common since brussels sprouts (everyone's favorite including mine) are expensive and sometimes not available frozen. I can't keep up with fresh stuff, I've got that to deal with for the bunnies. I get a five pound bag of frozen green beans and that lasts a week or two for the lot of them. Including the youngest cat, who gets in on the evening snack.
Other people have cut out 25 to 50% of the dog's food and replaced it with green beans for weight loss. The french cut are a good place to start as they are finer and mix in better until your dog gets to liking them.
Friend of mine has two older dogs that had gotten to be picky eaters and fat, and boy it was NOT doing them any favors. You get those old stiff joints and add a few pounds and it ain't pretty. She cut their kibble in half and replaced it with veggies (green beans or brussels sprouts) mixed with a little canned food, and the next thing she knew they were eating better, melting like butter, and looking and feeling much better. To see her oldest one romping and playing again at age thirteen has been wonderful for her. It's really worth a try.
susan
Fuzzy Wuzzy was a wabbit, Fuzzy Wuzzy had a dandelion habit! RIP little Wuz... don't go far.