Gizmo had his yearly vet appt this past Saturday and he got a little chunky over the winter

! He weighs in at 11 1/2lbs! My vet told me he should be around 8 lbs. to be at a healthy weight. My question is about bully sticks. I know they are good for him to chew on and he has about one bully stick a day, is this ok if he's on a diet? Are they fattening? Thanks in advance!