Dogs, much like many other animals, go through weight changes every now and then. Too many treats and stolen snacks will result in a few extra inches around the waistline, but not enough of the right food can easily lead to malnutrition. Diet isn’t the only thing to cause weight loss or gain in dogs, however.

If your dog has been losing a bit of weight lately, you should probably read ahead.


  1. What is Considered Dog Rapid Weight Loss?
  2. Why Is My Dog Losing Weight?
  3. Other Causes of Rapid Weight Loss in Dogs
  4. How to Treat Unexplained Weight Loss in Dogs
  5. Online Vet
  6. FAQ

What is Considered Dog Rapid Weight Loss?

Let’s pretend you have an overweight pup, and your vet puts them on a lower-calorie, higher-exercise regime. They would expect your pet to lose between one to five pounds every month-or-so, but it does depend on a wide number of variables. These include:

  • Start weight;
  • End weight goal;
  • Medical conditions and disabilities;
  • Age;
  • Lifestyle;
  • Home conditions;
  • And more.

Heavier pets tend to lose weight faster than lighter ones because of how much weight they need when exercising. A severely overweight pooch losing five pounds per month wouldn’t be seen as abnormal. If a very slim or underweight pooch were to lose five pounds in a month, on the other hand, the transformation would be obvious and sometimes quite alarming… and potentially fatal.

As a general rule, rapid weight loss in dogs would be the quick loss of 10% of their original body weight. My British bulldog weighs 50 to 60 pounds. Georgie-boy would need to lose five to six pounds of weight, quickly, to experience “abnormal” or “rapid weight loss”.

Why Is My Dog Losing Weight?

According to a vet analysis, there is a very long list of medical conditions and scenarios that could cause a dog to lose weight. Some are completely benign and have nothing to worry about.

If you have recently moved from an apartment to a house with a garden, your pooch will have lots of new space to get used to. There’s a chance they will zoom around for a few days or weeks (or possibly forever), which could cause a sudden onset of weight loss.

A change in the home isn’t the only thing that can cause a dog to get a little out-of-sorts. A change in food can affect your pooch’s weight alongside very hot or cold temperatures, a harsh change in climate, short-term illnesses (such as a spot of food poisoning), old age, and more.

Medical Conditions that Cause Weight Loss in Dogs

  • Early stages of pregnancy;
  • Cancer;
  • Heart conditions;
  • Oral or dental pain or problems;
  • Tapeworm;
  • Diabetes;
  • Liver failure or diseases;
  • Kidney failure or diseases;
  • Addison’s disease.

As a final note, German shepherds commonly suffer from exocrine pancreatic insufficiency, also known as EPI. This condition causes a range of symptoms similar to food poisoning or an upset stomach, including weight loss.

Old Dog Weight Loss: Why It Happens

Older dogs tend to experience weight loss for the same reason that older humans experience the same: decreased appetite, reduced digestive system efficiency, and reduced muscle performance.

When older dogs lose weight for natural reasons, the process is slow and gradual. You may not even notice it for a while, especially if your pop is a large breed, a very hairy breed, or very overweight.

Weight loss that happens quickly in senior dogs is a cause for concern and should be checked out by a vet.

Why is My Dog Losing Weight and Eating?

If your dog is eating fine, drinking fine, going to the bathroom fine, and behaving fine, it’s a good idea to get any rapid weight loss checked out. Also, are you 100% sure your dog is eating fine? Could it be the case that another animal, a pest or domestic, is eating their food?

If it seems that your dog is eating more than usual, it could be the case that they’re dealing with a parasite. Hookworms and other intestinal worms can cause rapid weight loss in dogs with regular or even increased eating and drinking patterns.

Your dog’s diet might not be right, too. If you’ve been feeding them the same thing since they were a year old, and they’re not in their teens, you’ve not adapted their food to suit their needs.

The dietary needs of a very young pup are very different to the dietary needs of a senior dog.

What About a Dog Losing Weight and NOT Eating?

If your pup is not eating, you’ve found the cause of their weight loss. Now it’s time to find out what’s causing the loss in appetite…

Dental problems can cause a dog not to want to eat. Would YOU want to eat with raging toothache? A broken tooth, gum disease, and oral cancer can put a pup right off their food. Depression, stress, and anxiety can also do the same thing.Dental problems can cause a dog not to want to eat. Would YOU want to eat with raging toothache? A broken tooth, gum disease, and oral cancer can put a pup right off their food. Depression, stress, and anxiety can also do the same thing.

I know you don’t want to talk about the C-word because it’s scary and awful, but if your pup isn’t eating (and even sometimes when they are), it could be the case that their weight loss is caused by cancer.

Why is My Dog Losing Weight and Drinking Lots of Water

If the weather is very hot outside, it could be the case that your pup has had enough food and is just feeling the need to guzzle down lots of cold water instead. We’ve all been there, right?

If the temperature is perfectly normal and nothing else seems to be the obvious cause, your vet will perform checks for things like diabetes. This commonly comes with weight loss, an increase in fluid intake, and an increase in urination alongside lethargy.

Other Causes of Rapid Weight Loss in Dogs

The list is long (I did warn you), and alongside the medical conditions I’ve already mentioned, the following are medical conditions accompanied by rapid or extreme weight loss:

How to Treat Unexplained Weight Loss in Dogs

You will need to get to the root cause of your dog’s weight loss before you can successfully treat it. It is likely that you will need a vet to first diagnose the problem, and then administer the treatment and/or care.

If the problem is simple, such as the wrong kind of food, a change should make things better. It is not recommended to suddenly and regularly change your pet’s food, though. Some furballs really do not like that.

Once the problem or condition has been diagnosed, the right kind of treatment can be given. With cancer, that might be radiotherapy or chemotherapy. If the problem is irritable bowel disease, a change to the diet will make a big difference. Other conditions, such as blockages, might require surgery to put right.

The only way to find out what treatment your dog’s weight loss needs is to first investigate and diagnose it.

Online Vet

If you’re not sure if your dog’s weight constitutes rapid weight loss, why not have a chat with one of Petcube’s online vets? They’re available around the clock, via video call, so they can take into the appearance of your four-legged friend and recommend a suitable course of action.

For less than $1 per day, you’ll get access to licensed vets around the clock… and you can ask those ‘silly’ questions you’re too afraid to ask your own vet!


Can dogs lose weight after being neutered?

Yes, they can. The anaesthesia and surgery can cause a pooch to lose their appetite for a little while, which can cause a little weight loss. Rapid weight loss following any surgery or treatment should be reported to your vet.

Can dogs lose weight from fleas?

Yes! Fleas are awful for your pup to have to deal with. As well as being irritating and itchy, the blood-sucking bugs can also, quite literally, suck too much blood. A severe, untreated infestation can cause anemia in dogs.

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