Fiber for dogs

tomorrow i am picking up a 9 month old male boston from a rescue. I'm going to be his new foster mom. the foster mom that has him now, says that he some times has loose stools(sounded often) and it sounds like he is on primium food now(ill find out what it is tomorrow) but she was telling him that he might benifit from a high fiber diet. Do any of your bostons need to be on a fiber diet? what are you feeding them? and Do you hadd any other fiber treats to the food?

Here is a list of fiber foods i was going to try and add to his food, are all of these safe for dogs?
red kidney beans
broccoli
green beans
brown rice
apple with skin
garbanzo beans
carrots
potatoes
sweet corn

I'll try and get photos of the lad here soon!
Thanks!