Unexplained Weight Loss in Dogs: Why Is My Dog Losing Weight?

Weight loss is one of the potentially quiet symptoms that I find quite scary.

If your dog has been overweight, you are likely to welcome that the pounds are coming off. But unless it’s happening because you’re taking deliberate steps such as changes in lifestyle and diet, do take note.

Further, things might overlap. Just because you’re trying to get your dog to thin out, it doesn’t always mean that’s why it’s happening. Read Beaner’s story to learn how complicated things can get.

Potential causes of abnormal weight loss in your dog include:

  • poor diet
  • anorexia
  • stress
  • intestinal parasites
  • GI disease
  • dental
  • diabetes
  • Addison’s disease
  • kidney disease
  • liver disease
  • heart disease
  • cancer
Unexplained Weight Loss in Dogs: Why Is My Dog Losing Weight? Weight loss is one of the potentially quiet symptoms that I find quite scary.

The big picture

Considering the big picture, take a look at the following:

  • how much weight has your dog lost and how rapidly
  • were there any dramatic changes in your dog’s exercise, lifestyle, and diet
  • is your dog hungry or refusing to eat
  • are there any other symptoms

Should you be freaking out? Probably; especially when your dog is losing weight rapidly. Potential scenarios that can cause unexplained weight loss in dogs include:

  • your dog is not getting sufficient nutrients
  • the nutrients are lost
  • the nutrients are not absorbed or utilized by the body

Other symptoms of concern include:

  • loss of appetite
  • ravenous appetite
  • vomiting
  • diarrhea
  • skin and coat changes
  • altered drinking and urination
  • changes in behavior
  • changes in habits and routine
  • panting, difficulty breathing or coughing
  • reduced activity or exercise intolerance
  • lethargy
  • restlessness
  • distended abdomen

Your dog is not getting sufficient nutrients


It does make sense to take a close look a the diet, especially if you recently changed your dog’s food. Don’t think that only inferior foods can cause problems—even an expensive brand can cause trouble.

For example, at one time, we experimented with various freeze-dried foods. One of them we tried contained turkey and chickpeas as main ingredients—sounds great, doesn’t it?

The chickpeas were ground into relatively fine grit visible after adding water. What I noticed, however, that my dog’s poop was full of identical particles. However, nutritional chickpeas might be, they went through my dog untouched by the digestive process.

No matter how wonderful the ingredients in your dogs food sound, they are useless of the body cannot use them.


If your dog isn’t eating, naturally, they’ll start losing weight. Food is essential to survival, though, and dogs instinctively know that. Generally, dogs won’t begin to refuse food unless they are seriously stressed, ill, or in pain.

It is imperative that you figure out the reason behind your dog’s anorexia. Some potential causes include:

  • severe stress or anxiety
  • serious illness
  • pain
  • fever
  • severe dental disease

Further information: Loss of Appetite in Dogs: Why Did My Dog Stop Eating?


If your dog regurgitates, it means the food doesn’t even reach their stomach. While different from vomiting, regurgitation can lead to starvation.

Further information: Regurgitation in Dogs: Is It Different from Vomiting?

Dental disease

Anything that interferes with chewing or swallowing results in reduced interest in eating. Dental disease is one example but other conditions, such as masticatory myositis can have the same outcome.

Kidney or liver disease

Any condition that causes nausea will reduce the desire to eat, and it can lead to weight loss.

Your dog is losing nutrients

Vomiting or diarrhea

If your dog is throwing up, they are likely to be nauseous and not eating—which would technically fall into the earlier category. However, even if your dog is eating, diarrhea or vomiting leads to a severe loss of water and nutrients. Depending on the severity, though, dehydration can be the more imminent threat.

It is essential to identify and resolve the reason your dog is having diarrhea or throwing up.

One situation is particularly of note—when your dog’s poop is greasy, slimy, and clay-colored. You might be looking at insufficiency pancreatic deficiency, which is a condition when your dog is unable to digest their food. Your dog will eat ravenously but still starve.

Further information: Excessive Hunger in Dogs: What If Your Dog Acts Like They’re Starving?


Intestinal parasites can literally steal the nutrients your dog eats. While this problem is not as common as it used to be in the past, it can happen. Whipworms, in particular might be to blame.

Since whipworm infestation can also lead to loss of appetite, vomiting, and diarrhea, it is a double-whammy.


Some cancers have high metabolic demand and will rob the rest of the body of calories. Further, associated pain can make your dog lose interest in eating.

Kidney disease

The kidneys process blood by filtering out wastes and toxins, while preserving nutrients and water and sending back into the body. When the kidneys don’t function properly, it leads to accumulation of toxins in the blood and/or loss of nutrients through urine.

Further information: Kidney Disease in Dogs – Say What? Canine Kidneys and the Associated Verbiage

Protein-losing enteropathy (PLE)

Sometimes, nutrients, such as protein, can be lost in the strangest ways. In PLE, protein is lost be excessively leaking back into the GI tract after already being digested and absorbed.

Despite initially mild symptoms, PLE can become a life-threatening situation fast. This problem goes far beyond the nutrient loss itself.

Along with weight loss, signs include ambiguous things such as:

  • loss of appetite
  • vomiting
  • diarrhea
  • blood in the stool
  • lethargy
  • lethargy

Potential causes include GI disease, lymphatic disease, or heart disease.

Further information: Protein-Losing Enteropathy (PLE) in Dogs

Your dog’s body cannot absorb or utilize nutrients

GI diseases

Gastrointestinal disorders can lead to vomiting or diarrhea, resulting in nutrient loss. However, a diseased gut can also lead to malabsorption or maldigestion. What is the difference?

Maldigestion means that the GI tract cannot break nutrients down to their basic building blocks. Unless the food is taken apart into usable bits, it cannot get absorbed and passes through the digestive tract without the body being able to benefit.

Once the food is broken down/digested, the individual, broken-down nutrients pass through the intestinal walls for distribution through the body. If the intestinal wall is diseased, it is unable to perform this important part, which is referred o as malabsorption.

While the end result is pretty much the same, the causes are not.

Metabolic diseases

After nutrients are digested, absorbed, and sent into the bloodstream, they still need to make their way to where they’re needed—the cells.

For example, a condition such as diabetes means that glucose accumulates in the blood while the cells starve for it.

Losing fat versus losing muscle

A generalized loss of muscle mass, not just fat, is usually a sign of more serious diseases such as kidney failure, liver failure, heart disease, or cancer. Orthopedic or neurological diseases can lead to loss of muscle mass too.

Related articles:
Why Is My Dog Gaining Weight: Is It the Food?
Sudden Weight Gain in Dogs: Why Has My Dog Expanded in Front of My Eyes?

Further reading:
Abnormal Weight Loss in Dogs

Categories: SymptomsUnexplained weigh loss

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Jana Rade edited by Dr. Joanna Paul BSc BVSc

I am a graphic designer, dog health advocate, writer, and author. Jasmine, the Rottweiler of my life, was the largest female from her litter. We thought we were getting a healthy dog. Getting a puppy from a backyard breeder was our first mistake. Countless veterinary visits without a diagnosis or useful treatment later, I realized that I had to take Jasmine's health care in my own hands. I learned the hard way that merely seeing a vet is not always enough. There is more to finding a good vet than finding the closest clinic down the street. And, sadly, there is more to advocating for your dog's health than visiting a veterinarian. It should be enough, but it often is not. With Jasmine, it took five years to get a diagnosis. Unfortunately, other problems had snowballed for that in the meantime. Jasmine's health challenges became a crash course in understanding dog health issues and how to go about getting a proper diagnosis and treatment. I had to learn, and I had to learn fast. Helping others through my challenges and experience has become my mission and Jasmine's legacy. I now try to help people how to recognize and understand signs of illness in their dogs, how to work with their veterinarian, and when to seek a second opinion. My goal is to save others the steep curve of having to learn things the hard way as I did. That is the mission behind my blog and behind my writing. That is why I wrote Symptoms to Watch for in Your Dog, which has turned out being an award-winning guide to dog owners. What I'm trying to share encompasses 20 years of experience. Dr. Joanna Paul BSc BVSc is our wonderful sponsor and has been kind to edit and fact-check my important articles.

  1. Sudden weight loss is always something to be concerned about! I try to watch what my dogs eat pretty closely (and measure their food), so if they gain or lose weight, we know it is probably a health issue.

  2. This is very detailed and helpful information. When your dog suddenly starts dropping weight, it can be a frightening experience. A few years ago, my girl Dav suddenly dropped 20 lbs in just a month. Far more than one could shrug off as being nothing… When we went to the vet to have her examined, they started running a series of tests to determine whether she was having any issues with her organ function. I will never forget how worried we were waiting for the results! In her case, it was determined that she suffers from IBD and the weightloss was the result of a flare up preventing her from absorbing the nutrition that she needed. Luckily, something that is totally manageable, we just had to learn the ropes!

  3. This is a very detailed list of potential causes. Some I was familiar with, however honestly would never have though of dental or PLE causes. This is a very helpful post.

  4. Great tips and hints that arms people to discuss with their dog’s vet! Watching our dog’s weight has become something we do with regular checking (scale in our vet’s office). This is due to having a dog with renal disease and the first sign was weight loss (as you mention above). Will share!

  5. Great advice! My dogs’ weight is one thing I keep a pretty close eye on. Although if I’m honestly, I mostly monitor to make sure they don’t gain too much weight! At least I’d notice pretty quickly if they lost it instead, though, and a concerning amount of weight loss would certainly warrant a trip to the vet.

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