Some dogs act hungry all the time and scavenge for food whenever they can. This is a symptom of imbalanced metabolism, and needs treatment beyond diet adjustment. A dog’s constant hunger is referred to as polyphagia and stems from factors like boredom, stress, genetics, poor-quality food lacking nutrients, or learned behaviour. However, it can also be a sign of serious medical issues like diabetes, hyperthyroidism, parasites, or nutrient malabsorption. Seek the advice of a vet to rule out an illness.