Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
Now to start we do have to appreciate that treats are not a required part of the diet. In fact, positive reinforcement with training is just as important (if not more so) then a food based motivation. So, we do need to make sure that our dogs are not training us to be dispensing treats they do not truly need.
Now you are right to be concerned about avoiding weight gain when giving treats. To do so, I would note that we can offer any treat we like as long as we are removing that calorie "cost" from their daily ration. So, you could give a set number of favourite treats as long as you were removing a calorie equivalent from his meals. Alternatively, you can even use kibble from those meals as your treat. That way you are directly removing the calories and redirecting them for treat use without accidentally feeding an excess of food/calories.
Otherwise, in regards ***** ***** calorie options that we can use as a health treat for our dogs, we will often use fresh veggies or fruit. For example, carrots, broccoli, cauliflower, radishes (my own dog's favourite), and apple (with the core removed) are all safe, low fat foods that can be used as treats for our dogs. Of course, avoid grapes, raisins, garlic, onions and raw potato as these are toxic for dogs.
Finally, just to note, as obesity is a growing concern for many dogs, there are also a range of DIY low fat/calorie dog treat recipes (example of low fat carrot dog treats-- HERE) available that you can try.
Overall, it is not so much about what the best treat is; but rather consciously thinking about how this treat fits in with his daily food/calorie needs. So, if we want to feed a commercial treat, its fine as long as we balance his diet to match the calories in that treat. Otherwise, we can use a portion of his kibble ration, make our own low fat treats, or use low fat veggies to remain guilt-free when offering treats and keep him healthy.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,