I've noticed over the past few months that my dog Joey seems to be losing weight. We haven't changed his food, and he seems to be eating okay. What could be going on?

Entire textbooks have been devoted to the subject of disease situations that can cause weight loss in dogs, so there isn't room here to describe every possibility. We can, however, touch on a few of the more common underlying diseases.

In younger dogs the possibilities that are seen more frequently include exocrine pancreatic inefficiency (EPI), inflammatory bowel disease (IBD), and parasites. With EPI, the dog is not able to properly digest his food; in IBD, he is not able to absorb enough nutrients from that food. In both of these situations you usually see diarrhea as well. There are many intestinal parasites, such as roundworms, hookworms, whipworms, tapeworms, coccidia, clostridium, and giardia, and some of these are potentially transmittable to people.

Diseases affecting the heart, liver, and kidney also cause weight loss, as do diabetes and cancer. These tend to be more frequent in older dogs, although they can be seen in younger dogs as well. Tumors, regardless of location in the body, suck nutrients from the bloodstream to support their growth, so even if the tumor isn't in the dog's intestinal tract it could still cause him to lose weight.

Bottom line, unless you have switched Joey to a light diet and increased his exercise, his weight loss could be a symptom of a serious illness. It is critical that you take him to your veterinarian. Along with a thorough physical examination, your vet will probably recommend a stool sample, bloodwork, and maybe X-rays in order to rule-in and rule-out a number of these possibilities.