The best way for a canine to maintain a healthy weight is to be fed a biologically appropriate diet that aligns with their activity level.
Dogs, Canis lupus familiaris, share nearly an identical digestive tract to their closest ancestors, the wolf, Canis lupus. Therefore, a beneficial diet consists mostly of animal protein. Some argue that throughout the domestication process of wolves, they’ve evolved to eat food scraps leftover from people. Although canines do have the ability to absorb a small percentage of nutrients from fruits and vegetables, most of these nutrients act as fiber and/or carbohydrates.
A truly biologically appropriate diet provides a wide variety of health benefits. This type of unprocessed diet with the nutrients intact in their natural state provides the necessary moisture and helps the body perform its natural functions. This diet is easier to digest, allowing the digestive system to work less hard in order to absorb full nutritional value from the food. In particular, a diet that consists of raw meat will result in smaller poops, cleaner teeth and healthier gums from the live enzymes, relief from allergies or food intolerances, and many more benefits.
Discussing the transition to a more meat-based diet, with a veterinarian certified in nutrition can be a great idea. Supplementing some amount of meat into the diet will bring health benefits that could potentially help to save money on vet bills later on in life.
In order to lose weight, a dog must be fed a diet with fewer carbohydrates. Thus, transitioning to a diet that includes a higher percentage of protein and a lower percentage of carbohydrates would help the body perform other processes in the body and spend less energy digesting complex carbohydrates which bind the nutrients in kibble together.
In order to gain weight, a dog would also need to be fed a more biologically appropriate diet in order to build lean muscle mass, rather than fat.