Why is My Dog Losing Weight Suddenly? Causes and What to Do

Weight is an essential factor in a dog’s health. It can indicate or cause a health problem. Any unnatural pound gain or loss can be concerning for a pet owner.

Of course, you never want your pup to be overweight. If they are, it may be a relief when they lose some pounds.

That said, sudden weight loss can indicate a serious issue, especially if your pup is still eating normally. Excessive sudden loss of 10% of a dog’s normal weight can indicate an issue.

Many things can cause sudden pound loss. The obvious factor is a diet change, but there are other serious causes you want to eliminate like heart disease or kidney disease.



Diet changes are an obvious potential cause of a dog’s weight loss. If you change foods and notice your pup losing pounds suddenly after, the food may be causing it, either from a nutritional issue or because your stubborn pup refuses to eat it.

Even if you changed food to get some pounds off your pup, it should happen naturally and they should still be healthy. They shouldn’t suddenly lose 10% of their body mass or show any other signs of a digestive issue.

Make sure your companion has adjusted to their new food properly. Also, make sure that they are actually eating the new food. If they aren’t eating for any reason, they’re obviously going to lose pounds.

1 puppy with toy
Many things can cause rapid weight loss in dogs, including diet changes.


Dogs may be more susceptible to weight loss as they get older and have metabolism changes. This may mean that they need a diet change, or it could be connected to another health problem associated with aging.

My family had an old German Shepherd who once lost weight until she was almost skin and bones in a few months. The food she had been eating her entire life wasn’t giving her what her older body needed.

Once we got her on better food for seniors of her breed, she gained some of the pounds back. She was never as big and strong as she was in her golden years though.

Make sure you’re taking your senior to the vet often to get checked. Age can bring many other diseases because of their weakened immune system.


Diabetes Mellitus is a serious disease that may sound familiar to humans. Canine diabetes causes a dog to lack the insulin needed to break down blood sugar. Lack of insulin can cause serious physical problems for our bodies, including rapid weight loss.

If your pup has canine diabetes, they should show other signs. They may drink more water, be hungry more, and urinate more. You may also notice cataracts.

If you suspect your pup is developing diabetes, get them to the vet so they can run tests. Your pup may need insulin injections or a special diet.

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Dogs may lose pounds as they age due to metabolism changes. Food that worked for them before may not work anymore.

Gastrointestinal Disorders

Gastrointestinal disorders may affect your dog’s digestive system and its ability to break down food. This can cause weight loss no matter what foods you try switching to. Dogs suffering from GI issues will also vomit excessively and have consistent diarrhea.

Dogs with GI disorders can’t retain nutrients because of the constant vomiting and diarrhea. If left untreated, your pup will keep getting thinner. If you notice any of the symptoms, it’s important to get to the vet for treatment.


Parasites are always a dangerous but legitimate threat to your dog. If your companion is rapidly getting thinner, it’s always a scary possibility you want to rule out.

Parasites in the intestines like intestinal worms can cause your pup to lose their appetite or they can suck the nutrients out of the food they’re eating. This can naturally cause rapid weight loss. Your pup may also experience vomiting, diarrhea, or a decreased appetite.

These little demons can be rooted out and killed with medications and treatments from a vet. Make sure you get your pup into a clinic if you suspect they have any parasites. Also, make sure you’re keeping your pup up to date on all preventatives. Keep dewormers on hand.

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Parasites can cause a dog to lose their appetite or lose nutrients from the food they’re eating.


Cancer is always a scary thought, but it can happen to anyone, even our furry family members. Any cancer can be deadly if allowed to progress for too long. It’s important to watch and intervene early if you suspect your pup has it.

Several types of cancer can cause sudden weight loss, so it’s hard to tell which one is causing it without a vet’s help. Treatment will likely depend on what type of cancer your pup has. They may need surgery or chemotherapy. Early intervention is key.

Heart Disease

Heart disease is a severe problem, but it may not cause weight loss until after it’s progressed. Sometimes you may even notice your companion seems to gain weight instead despite losing their appetite, which can be equally concerning. It can mean fluid is accumulating in the body.

Dogs suffering from heart disease may have trouble exercising and may often feel weak. They may also suffer from coughing and other breathing difficulties. They could even lose consciousness from a lack of blood in the brain.

If you notice any of these issues, you should get your friend to the vet, preferably before they start getting thinner.

Kidney Disease

Kidney disease is another severe disease where your pup may get thinner after the disease has progressed. As the disease progresses, they lose their appetite and eat less. At this point, you’ll probably also notice vomiting and dehydration. They may also need to urinate more.

Kidney disease is linked to older dogs, so make sure you’re keeping an eye on your senior. As they age, their kidney functions start to deteriorate.

4 two dogs nuzzling
Heart disease and kidney disease can both cause weight loss as they progress.

Stress and Anxiety

We may not always think about it as much as we should, but stress can have a pretty big impact on health, including weight. This is true for humans and pets alike.

A stressful environment can negatively impact your pet’s physical health if you’re not paying attention. Stress and anxiety can make your pup uncomfortable eating or affect their immune system.

Make sure you’re paying attention to your pup’s mental and emotional health as well as their physical health. If there’s a stressful situation like a family loss, new home, or new family member, make sure you’re watching for any signs of excessive stress in your companion and look for ways to manage it.

Make sure your pup is still eating their food and has a safe space to take their time eating, drinking, and resting.

Calling the Vet

Sudden, unexplained weight loss is usually a red flag of something serious. It’s always worth at least calling the vet, especially if you can’t think of a reason why your friend is suddenly getting thinner.

Something may be killing their appetite, or they may have a serious illness. It’s especially crucial if you’re dealing with a senior whose immune system isn’t as strong as it used to be.

Knowing your pup’s body condition score can help you determine if there’s a problem. To check your companion’s body condition score, there are a few tests you need to try.

  • Run your hands over their ribs. You should be able to feel a layer of fat over them, but not too much
  • Look at your pup from above. You should see an obvious waistline that doesn’t blend in with the hips
  • Look at your pup from the side. You should see a waistline that tucks toward the waist and not a straight line from the chest to the back legs

You should also be getting your pup weighed regularly and have an ideal weight range for them based on their breed. Don’t be afraid to ask for a vet’s assistance if you’re unsure what their range should be.

If your pup has suddenly lost a significant number of pounds or you can easily feel their ribs, get them to the vet. Take note of any lifestyle changes you’ve noticed or any other issues like vomiting, dehydration, or the runs.

It’s always better to be safe than sorry. If you think your companion is sick in any way, it’s worth the vet call.

5 bulldog back
Sudden, unexplained pounds loss is always a red flag and warrants a call to the vet.

Track Your Dog’s Weight

Natural weight loss can be a good thing if you were worried about them being overweight. But sudden pound loss, especially to the point of being able to feel or see ribs, is a huge red flag that shouldn’t be ignored. It can indicate a food problem or a serious health problem. It can also be a sign of parasites.

Sudden weight loss is always worth calling the vet over, especially if you think your companion is in any pain. If you do need to make the call, make sure you take note of any other symptoms. It can help them determine potential problems and what tests to run.

Make sure you know your pup’s normal body composition and ideal range so you know what is and isn’t normal. Keep a scale around so you can easily weigh them if necessary.

Make sure you’re taking your pup to the vet regularly to check for problems like heart disease and kidney disease, especially as your dog gets older. And make sure you’re taking steps to prevent parasites.

Take sudden weight loss (and gain) seriously. While a little fluctuation may be normal, sudden noticeable pound gain or loss can mean something dangerous.

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