6 Causes Of Sudden Weight Loss in Dogs, and How to Maintain a Healthy Weight

Unpredictable, sudden weight loss in dogs can be symptomatic of a larger issue, or it may just be because they are exercising more and eating less than usual. If your dog drops over 10% of his or her total body weight in a short period and with no discernable outside factors, then you should be concerned.

Just like with human beings, you need to keep tabs on your dog's weight since it is so often an indicator of health, like any other bodily change. Below we discuss six typical causes of rapid weight loss in dogs that you should watch out for.

Causes Of Sudden Weight Loss in Dogs


Weight loss in dogs resulting from parasitism is much less common than it was in previous years, thanks to a growing percentage of pets receiving monthly protection against intestinal parasites and heartworm. It would be best if you remembered that not all products are equally effective at staving worms off. In particular, there aren't a lot of products designed to kill whipworms.

Pets can contract whipworms by directly ingesting eggs from the environment, such as contaminated water or soil. Some symptoms of intestinal infection in dogs to watch out for are:

  • Weight loss
  • Vomiting (persistent or intermittent)
  • Diarrhea
  • Soft stool
  • Decreased appetite
  • Increased gas

Typically a fecal exam is required for a vet to diagnose intestinal parasites. The vet examines your dog's feces to look for eggs or other parasite life stages (depending on the kind of parasite in your dog's system). Treatment of intestinal parasites generally consists of a broad-spectrum dewormer, along with a monthly preventative medication to stop any reinfection.


There are many types of cancer that can cause unexplained weight loss in dogs. Cancer is typically more prevalent in older dogs, and malignant forms of cancer can be life-threatening. Several malignant cancers in dogs are directly linked to weight loss, like lymphoma, osteosarcoma, and hemangiosarcoma.

Weight loss due to these malignant tumors may occur both due to the metabolic demands of the tumor itself and because discomfort and pain are reducing the dog's activity and appetite. Other canine cancers, like oral melanoma, may make swallowing and eating a painful process, causing the dog to stop eating. 

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Advanced Heart Disease

Like those with kidney disease, pets with heart disease won't immediately start to lose weight at the start of the disease. Some dogs may even look like they're gaining weight (despite eating less) due to fluid accumulation in the body. Loss of appetite isn't always the easiest way to recognize if your pet's weight loss should be concerning.

If you notice a small amount of unexpected weight loss, you may want to add more calories to their diet. If your dog eats more and puts the weight back on, then they're probably okay. Moreover, make sure to isolate the food of the affected pet from the food the rest of your pets eat to lessen food stealing or sharing. To control the experiment, try your best to avoid feeding table scraps or too many treats

Related: Should You Start Giving Your Dog A Joint Supplement?

Kidney Disease

Pets with kidney disease, unlike some of the other conditions for which weight loss is a symptom, generally don't lose weight right away (as mentioned above with heart disease). Weight loss is usually correlated to chronic forms of the disease. If your pet is diagnosed with kidney disease after you've noticed them losing weight, then it's most likely they've suffered from the illness for a long time.

As the disease progresses, dogs typically don't feel well and deal with the loss of appetite, vomiting, and dehydration. This kind of weight loss from chronic illness typically impacts muscle and body fat, causing your pet to become emaciated.

Metabolic Disorders

Metabolic disorders like hyperadrenocorticism (Addison's disease) and diabetes mellitus can significantly impact the body condition of your pet. Metabolic conditions often display complicated clinical signs, and advanced diagnostic testing may be necessary to identify these conditions. 


Also known as Cushing’s Disease, hyperadrenocorticism is the overproduction of cortisol in your dog’s blood. A tumor in the pituitary or adrenal gland is usually the cause of excess cortisol. 80% of Cushing’s Disease cases are from a benign pituitary tumor. Another common symptom of Cushing’s Disease is hair loss. If your dog is losing weight and hair, it may have Cushing’s Disease.

Diabetes Mellitus

Diabetes mellitus is a disease that affects your dog’s ability to produce enough insulin for breaking down blood sugars. When insulin levels are unbalanced, it can cause severe weight loss in dogs along with the following signs:

  • Cataracts
  • Increased appetite
  • Frequent urination
  • Excessive thirst

If you suspect that your dog may have diabetes, you’ll want to contact your vet to create a management plan.

Gastrointestinal Disorders 

GI problems can cause weight loss over time, as excessive vomiting and/or diarrhea can make it difficult for your dog to retain nutrients. Both diarrhea and vomiting can be due to various causes, which is why you should speak with a vet to pinpoint the underlying issue. Maldigestion or malabsorption may affect the intestine's ability to break down and absorb essential nutrients from the diet.

Pets suffering from gastrointestinal disorders will typically be very underweight, no matter how their diet is changed until a medical solution is put into place.

Is It Normal for Dogs to Lose Weight as They Get Older?

Yes, as your dog ages, its metabolic rate also changes. Mature dogs actually need about 20% fewer calories than younger dogs to maintain their weight. So as your dog ages, you’ll want to feed them dog food that is specially formulated for their older age because it will have less fat and fewer calories. 

But as a dog matures from old to very old, it is very normal for them to lose weight. At this point, your senior dog may have a decreased appetite due to the lack of smell/taste, or they may have difficulty chewing or swallowing. 

If your older dog is losing weight but eating, then it may mean they need a higher-fat diet.  In this situation, you’ll want to increase their food's fat content and calorie content so that every bite counts.

Related: Ways to Improve Your Dog’s Gut Health & Digestion

How Do I Know if My Dog is Too Thin?

The best way to know if your dog is too thin is to take them to the veterinarian. Your vet can evaluate your dog’s body conditioning score. A healthy dog weight has an ideal body conditioning score of 4 or 5, according to the World Small Animal Veterinary Association

Tufts University’s Veterinary School states that when looking at your dog, if you can see the ribs, lower back vertebrae, and pelvic bones, then your dog may be too thin, and you should take them to the vet for assessment. A healthy dog will have ribs you can easily feel but not necessarily see. 

Rogue Pet Science makes all-natural supplements and treats that are high in Omega-3s and other essential vitamins to help with overall nutrition.

Related Link: Active Nutrition for Your Dog: Rogue’s Approach to Pet Nutrition & Performance

Does Walking a Dog Help Them Lose Weight?

Yes, in addition to veterinarian-recommended dietary changes, it is very important to walk your dog to help them lose weight. You should try to walk your dog for at least 30 minutes every day. 

If your dog is severely overweight, then you’ll want to take walks slowly and follow their cues by listening to their breathing. If your dog’s breathing becomes too labored, slow down or take a rest. Go at their pace and build up to 30-minute walks.

What Should I Do if My Dog is Losing Weight?

The best thing to do is call your vet. They’ll be able to assess your dog’s body condition and rule out any of the conditions that could be affecting your dog’s weight.

Should You Take Your Dog Losing Weight To The Vet?

Many of the common causes of weight loss carry similar warning signs or symptoms. You should evaluate the possible causes of your dog's symptoms and weight loss to figure out if you need to take a trip to the veterinarian.

Questions To Ask

If you've identified that your dog has been losing weight for no apparent reason, you need to think about some of the circumstances surrounding their condition. Here are some questions you should ask yourself:

  • Is your dog's coat sparse, coarse, or dull?- An unhealthy coat could be symptomatic of malnutrition, poor nutrition, or an intestinal parasite. A healthy coat should be smooth and shiny. Contact your vet if you notice a sudden change in your dog’s coat.

Want to improve your dog's digestion and coat? Shop Rogue Pet Science’s dog food toppers that fortify your dog’s muscles, coat, and overall gut health.

Related Link: Why Gut Health is Important for Dogs

  • Is your dog ill?- Any identifiable illness could be the cause of your pet's weight loss. You should be extra careful if the disease seems to last a long time. Prolonged, chronic illnesses can result in significant weight loss. 
  • Has your dog suffered head trauma?- A dog can get a concussion just like a human being, and resulting in nausea and dizziness can cause them to lose their appetite and lose weight rapidly.
  • Is your dog on medications?- If your dog is currently on a course of medications for an illness, the weight loss could be due to either the side effects of the disease itself or a lack of appetite as a side effect from the medications they're taking.

Why is my dog losing weight but still eating?

If your dog is still eating but losing weight, it may be a sign of a bigger problem. Your dog is either not eating enough calories to support its lifestyle or your dog may have a digestion or absorption issue.

Why is my dog losing weight and drinking lots of water?

Excessive thirst can be a sign of dehydration, illness, or reaction to a medication, or diet. But when your dog is losing weight at the same time, it might be a symptom of diabetes. You’ll want to contact your vet to assess your dog’s insulin levels. 

Related: Can Dogs Eat Eggs?

Related Link: How to Help Your Dog Gain Weight

If your dog experiences rapid, unexplained weight loss, there may be a variety of underlying causes. We recommend taking your dog to the vet to rule out any severe medical conditions or catch chronic illnesses early. Rogue Pet Science is a top provider of pet products. Our Origins Canine 5-in-1 is made with wild fish and packed with nutrients to nourish your furry best friend. Feed your dog the best treats on the market with Rogue Pet Science products today!

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