He might be bored. Does he have a job? LOL. Give him plenty of interesting things to do; toys, little obedience commands that you work on throughout the day....a little here, a little there and outside for two or three short training sessions and some romping. If he gets a little tired out, he may settle down a bit. Yes, it could get to be a habit...this in and out, in and out. Don't give in to it every time.
Where did you hear...or who told you that people food like meat and veggies aren't good for dogs? You can do your own research. There's a ton of online info and books. The premium dog food kibbles are all human grade meat, veggies a little grain, vitamins, mineral suppliments etc. It's just easier to feed as a kibble. Actually there's a lot out on feeding raw food and a lot of people swear by it. It's meat, sometimes veggies, sometimes a little grain, although grain is really not much of a natural thing for dogs. That's what we eat too. They're carnivores with an omnivore eating behavior, which means they're designed to eat meat (teeth, jaws, digestive system) but will eat just about anything they can find because they're not only hunters, but scavengers..opportunists. There are some things we eat though, which are toxic to dogs so it's good to find out about that....like onions, grapes, raisins, chocolate and a few other things I think.
You can brush teeth. They make a doggie toothpaste. Don't use human toothpaste...toxic to dogs. Any food, whether it's hard or not still gets stuck between their teeth.
Hope that helps a little and just make sure your dog goes when he goes outside and then you'll be more assured when you ignore his request to go out after only 5 minutes. LOL...the little devil. LOL.