I'm no expert, but my concern with "light" foods is that they have filler in them to make the dog feel full, and are not necessarily the healthiest choice.
I think for weight loss the key is to feed a very high quality food, with a lean protein source and limited carbs. Grain free would be the way I would go - no rice, corn, wheat, etc. since it is these carbs that the dog can't metabolize efficiently and which ultimately are stored as fat, leading to weight gain.
Personally I feed Orijen, but there are a few other grain free brands too, like Wellness Core. It is important to adjust serving size with these foods though. Some grain free foods have higher calories than regular kibble, so you need to feed a lot less. But since the dog metabolizes the food more efficiently and uses all of the food, the result is a healthier dog , including reduction of fat and increase in lean muscle mass.
Also, cut out snacks and increase exercise. He needs to burn calories. Particularly for a dog with hip issues, exercise can make a huge difference in minimizing symptoms and slowing down deterioration. Swimming of course is great, but steady work on land is good too. Marin has severe bilateral hd and hikes several miles a day. Slowly work Baloo up to an exercise regimen that helps him drop the pounds. Building up the muscles in his hip area is critical if you are seeing problem in his back end.
Hope that helps.
