Why Is My Dog Losing Weight?

Most people these days worry about weight gain more than loss, but if your dog is suddenly losing weight for no apparent reason, it can be a cause for concern. You may not notice weight loss until it’s pretty significant, especially if your dog has long or thick fur. Weighing your dog monthly throughout their life is a great habit to get into so you can spot trends in either direction quickly.

Body weight is a simple balance of calories in versus calories out, so if your dog loses weight, something has gone wrong with this balance. It could be that they are taking in fewer calories, the body is suddenly burning more calories, or the nutrients from food are not getting where they need to be. The reasons for this can be very varied. Let’s look at some of the common causes of sudden weight loss in dogs that’s unexplained or unexpected.

Causes of reduced calorie intake

• Lack of appetite, also called anorexia, may be due to many things. Your dog may become less interested in food because they feel unwell or nauseous due to illness such as liver or kidney disease or stress and anxiety, such as a new baby or big changes in the home.
• Pain. If your dog is in pain, they may be depressed or simply not want to move to actually go and eat. This may be particularly true if they have mouth or dental pain or pain in their neck.

Causes of increased calories burned

• Increased exercise. This may sound silly, but if you suddenly have more time to walk your dog, they’ve met a new friend to play with, or someone else is walking your dog more, then they may simply be exercising more and need more food. Talk to your vet about whether the food they are on is adequate.

• Pregnancy and lactation take lots of energy. If your dog is pregnant or feeding puppies, she will need ad lib puppy food to keep her energy balance right.

• Certain diseases, such as cancer and diabetes, may result in your dog eating normally or even more than usual but still losing weight.

Nutrients not getting where they are needed

• Almost any gastrointestinal disease can cause weight loss. The food your dog eats may pass through the gut too quickly to be properly absorbed, such as in cases of diarrhoea. A deficiency in certain enzymes may mean they can’t digest fat or one particular component of their food, leading to malnutrition and weight loss.
• Parasites, such as worms living in the intestines, can ‘steal’ a significant amount of your dog’s food. Always make sure your preventative healthcare is up to date and suitable for your dog’s lifestyle.

Should you be concerned?

Unless you’ve made a conscious effort to get some weight off your dog, any unexplained weight loss should be investigated. Try to be an observant owner. Has your dog’s appetite increased or decreased? Are they drinking more than usual? Have you noticed any diarrhoea or changes in colour or frequency of their stools? Could they be pregnant? Has something drastic happened at home, like a new arrival?

The more information you can give your vet, the better. They will almost certainly want to do blood and urine tests as well as the normal physical exam. If you can take a stool sample, that will help too.

As we said at the beginning, weight loss may be a very early sign of disease, so regular weight checks are essential for spotting things as soon as possible so you can get help. As always, if you are ever concerned or unsure, talk to your vet. It’s always better to be safe than sorry.

Reviewed by Dr. Hein Meyer, DVM, PhD, Dipl-ECVIM-CA