Dog with open mouth lying on grass

Likely reasons why your dog is losing weight

At some point as a pet owner, you’ve probably asked yourself, “Is my dog losing weight?” Unexplained weight loss can occur in all types of dog breeds. Sometimes there are harmless reasons why your dog is losing weight. Other times, there may be underlying conditions your dog is suffering from that are causing them to shed the pounds. So, what could be causing your dog to lose weight? James Wellbeloved looks at some of the most likely reasons for unexplained weight loss in your dog, and how to stop it in its tracks.

Signs of weight loss in dogs

If your dog is losing weight, you may have already noticed a decrease in their overall body mass; although this can be difficult to keep track of with some breeds, especially if they already have a slight build. It’s therefore a good idea to get clued up on the different ideal dog weights by breed, so you can check whether your pet is the right weight for their type.

Other signs your dog is losing weight include:

  • Chronic vomiting/diarrhoea
  • Loss of appetite
  • Lethargy

If your dog is exhibiting any of the above-mentioned symptoms, you should consult your vet immediately to get a proper diagnosis.

Common factors why your dog is losing weight

Unexplained dog weight loss can be unnerving for any pet parent, particularly if you don’t yet have an idea of the underlying cause. Here we’ve put together some of the most common explanations as to why your dog is losing weight:

Low-quality diet

A lack of nutrients often means your dog’s weight will start to decrease. Also, you’ll probably notice them becoming more sluggish and less engaged than usual. Consider switching your dog’s food to see if it helps increase their weight. Always make any changes to your dog’s diet slowly, by gradually increasing the ration of new food to original food, and when in doubt, always ask a vet for advice.

Worms and parasites

Worms and other parasites can cause your dog’s weight to drop. This usually only happens with severe cases though, so ensure your pet is well groomed! After their coat is pristine once again, your dog’s weight should return to normal.  Make sure that your dog is up to date with their worming and flea treatments too, and in the event veterinary assistance is required, do have them thoroughly checked over.

Dental disease

Oral pain brought on by dental disease in dogs may ultimately cause them to lose weight. Oral care problems can make eating very painful. Likewise, the bacteria can spread throughout your dog’s body, leading to loss of appetite and general feelings of unwellness. Dogs are naturally stoic animals, so therefore you don’t often know that they’re hiding pain. Fortunately, treating the underlying condition usually helps clear up infection and reignite your dog’s love of food.

Diabetes mellitus

This is a disease that can cause dogs to lose weight rapidly. A variety of additional symptoms also occur, such as your dog drinking more water than usual, urinating more frequently and seeming hungrier. The good news is a vet will likely be able to help you get your dog’s diabetes under control with insulin injections and a specialized diet.


Unfortunately, one of the symptoms of many cancers in dogs is unexplained weight loss, either due to the metabolic demands of tumours, or because pain and discomfort are causing reduced appetite and activity. Canine mouth cancers may make eating and swallowing more painful as well, meaning your dog will likely avoid food. As with humans, early detection and intervention are important to slow or even stop cancer progression in dogs, so if you suspect anything at all, head to the vet sooner rather than later.

Your dog could be losing weight for a variety of reasons, some of which are easily resolved with the right type of intervention. However, if their weight is consistently dropping, you should take them to the vet for an examination as soon as possible.