Super question! Fiber is important in your puppy’s diet because it helps him digest his food without too much difficulty. It is sometimes also a source of protein, depending on the particular ingredient in question. Some examples of fiber in the reviews above are:
Brown rice;
Rice bran;
Oat groats;
Oat hulls;
Dried spinach and kelp; and
Pea fiber.
If you’re ever in doubt, it helps to know that fruits, veggies, and whole grains are generally fiber-rich. It’s good to know!