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6 Causes of Unplanned Weight Loss in Dogs

Dogs that lose weight for no reason need to be checked by the vet.

If you look at your dog one day and realize that she has lost weight without you changing her diet or exercise plan, something is likely wrong. Here are the most common things that cause unplanned weight loss in dogs.


Parasites in dogs can sometimes cause unplanned weight loss, although it is not particularly common today because most dogs receive a routine general de-wormer in their monthly heartworm preventative.

However, a puppy that doesn't gain weight well or an older dog that is losing weight should always be tested for intestinal parasites.

Kidney Disease

Kidney disease is a fairly common condition, especially in older dogs. As the kidneys become unable to remove toxins from the bloodstream effectively, the dog becomes sick and begins to lose weight.

Many veterinarians recommend routine blood tests as a dog ages because conditions such as kidney dysfunction may be caught and managed earlier.

Because it can be difficult to tell by looking at her that your dog has lost weight until it is pretty advanced, it is a good idea to make a habit of routinely weighing your dog so that you can notice gain or loss more quickly.

Dental Problems

Dental disease such as gingivitis, periodontitis, oral abscesses, oral tumors, loose teeth, and broken teeth can all cause a dog to have difficulty chewing. While dogs with dental disease might not always lose weight, it is something that should be examined by the veterinarian in cases when a dog has unexplained weight loss.

If you notice that your dog is losing weight and you have not changed his diet or exercise program, make an appointment with your veterinarian right away.


Many types of cancer in dogs eventually cause weight loss. Depending on what type of cancer and where it is, the disease may be significantly advanced before weight loss occurs, but in cases of intestinal cancer, it might happen early in the disease process.

Diet Change

Sometimes, changing a dog's diet may result in weight loss, especially if the new diet has fewer calories per cup than the previous one. If your dog is losing weight but not showing any other signs of illness, be sure to give some thought as to whether you have changed her diet in the last few months.

Diabetes Mellitus

One common cause of fast weight loss in a dog that is eating normally or even ravenously is diabetes mellitus. Usually, increased water consumption and urination are also observed in these dogs.

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Diabetes in Dogs

Obesity in Dogs: Overview of Causes and Dangers

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Warning Signs of Cancer in Dogs

Dog Worms: Canine Intestinal Parasites

Hands-On Guide to Checking if Your Dog Is at a Good Weight

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