Hi Cdubau,
In regards to weight loss the balance between caloric expenditure and intake is the most important factor in success. If the dogs are not losing weight at the current amount being fed than caloric intake needs to decrease or expenditure needs to increase. Having your dogs evaluated by your vet to make sure that medical conditions are not playing a role is a reasonable thing to do.
Wellness recommends to use their package recommendations as a starting guide. You may still have wiggle room here to adjust downwards but I understand your concern to meet nutrient needs. As my own dog has low caloric intake requirements it is something I monitor. Using a nutrient analysis from the company, your dog’s weight and amount fed the intake can be calculated and compared to NRC requirements.
You may need to switch diets if you are not meeting nutritional needs at the caloric intake needed to lose weight.
Throughout weight loss you want to feed a high proportion of calories from protein, this is different than saying a high protein diet. A diet can be “high” in protein on a percentage basis but not on a calorie basis depending on the fat value of the diet. People differ in their recommendations to feed the energy calories from carbohydrate or fat. There are a few studies on this to guide us. In Romsos’ study, dogs fed a diet 25% protein calories, 62% calories as carb and 13% as fat were leaner and gained weight less efficiently than dogs fed 25% protein calories 0% carb calories and 75% fat calories. In Kim et el when keeping total calories fed the same, increasing the percent of calories from fat by about 8% doubled trunk body fat in 12 weeks while weight remained the same.
In regards to weight loss, when fed a low fat diet and holding fat calories constant, weight was loss was greater when more calories were fed as protein vs carbohydrate (Bierer). I think this is where people assume that low carb diets are preferable for weight loss. However, when keeping the percent of calories fed as protein constant dogs lost more body fat when fed a greater percentage of calories as carbohydrate and fewer percent of calories as fat (Borne) . There was a confounding variable in this study though as the low fat diet was also higher in fiber. The lower fat/higher carb group lost more total weight than the higher fat/ lower carb group but it didn’t differ significantly between the two groups. However the percent of fat loss was significantly greater in the low fat/ high carb group vs the low carb higher fat group.
Putting this all together, based on current research, feeding a high percent of calories from protein and a low percent of total calories from fat and letting the carb calories fall where they may is likely the best composition for a weight loss diet for dogs.
