It is likely that there are internal parasites. Bugs will take away the nutrients in the food, and the dog will become thinner and thinner, but will eat more.
You can feed your pet internal anthelmintics to deworm your pet, which is effective against up to 18 kinds of internal parasites such as roundworms, tapeworms, and whipworms. Internal parasites are diseases common to humans and animals. Food, drinking water, mosquitoes, fleas, etc. are all vectors for transmission, so regular deworming is necessary. Feeding some intestinal probiotics during deworming can reduce the occurrence of stress and relieve gastrointestinal discomfort.