Dog losing weight: A vet's guide to causes and treatment

Dog losing weight: Chocolate Labrador lying on couch
(Image credit: Getty Images)

Are you concerned about your dog losing weight?  Weight loss occurs when the body is not getting sufficient calories and nutrients to meet its needs.  Sometimes weight loss can happen even if you feed your dog enough food.  There are a number of factors and medical conditions that can cause this imbalance, and some of these causes are more serious than others.  Your dog’s weight is a good indicator of their overall health and it is essential to pay close attention to any changes.  Here are some common causes of weight loss in dogs and what you can do to address these issues.

Increased activity

When your dog is getting more exercise, their body is burning more calories. To keep up with these energy demands, your dog has to consume more calories. If your dog's diet and calorie intake are not modified to account for the extra activity, your dog will start to lose weight. For some pets, shedding a few extra pounds may help them get to a more appropriate, healthier weight. For others, a change in diet is necessary to prevent them from losing too much weight and to accommodate the increased activity levels. 

If you have concerns about whether or not your pet is consuming enough calories, schedule an appointment with your veterinarian. They can help you evaluate your pet's diet and exercise regimen.  If extra activity does not explain your pet’s weight loss, your vet can also look for other reasons your pet may be losing weight.

Pain and weight loss 

Pain can make eating difficult and it can decrease your dog's appetite. Different types of pain can affect your dog’s eating habits, but mouth pain is the most common. A damaged or infected tooth can make chewing kibble an excruciating task. When eating becomes painful, pets are less likely to consume enough food and will start to lose weight. Brushing your pet's teeth and making sure they get routine dental care is critical to keep your pet's mouth healthy.

Orthopedic pain and other forms of pain can also decrease your pet's appetite. If your pet is usually a good eater and suddenly stops finishing their meals, this should be a red flag that indicates something is wrong. Pain that is not addressed or adequately controlled can lead to ongoing inappetence and weight loss. Determining the source of the pain and relieving it is essential to get your pet back to living a happy, comfortable life.

Digestion issues 

Dog losing weight: Dog lying on the couch

(Image credit: Getty Images)

Hamster and an abacus

(Image credit: Getty images)

There’s no NHS for pets. Veterinary care can be eye-wateringly expensive and most pets will need treatment for an illness or injury at some point in their life. It’s difficult to think about your animals being hurt or unwell, but you need to ask yourself: what would you do if you were faced with a vet bill for hundreds or thousands of pounds?

Compare Quotes for Pet Insurance from GoCompare

Consumption of food is only the first step in ensuring your pet gets the proper nutrition to fuel their body. Once the food is consumed, the body needs to break down the food and absorb the nutrients. Gastrointestinal disorders can disrupt this process and prevent the body from getting proper nutrition. When dogs vomit or experience diarrhea, calories are lost, and nutrients are not adequately absorbed. 

Chronic diarrhea can be a sign of irritable bowel syndrome, parasitism, or other gastrointestinal disorders. Over time, these digestion issues can lead to weight loss because the body is not getting enough nourishment.  It is essential to determine the underlying problem to get your dog's health back on track. Often times this requires diagnostic testing performed by your veterinarian and possible changes to your pet's diet. Without the appropriate care, your pet may continue to lose weight even if they maintain a healthy appetite.

Metabolic disorders 

Several metabolic disorders can contribute to weight loss in dogs. These can include conditions such as diabetes mellitus and hypoadrenocorticism, more commonly known as Addison’s disease. Pets suffering from these conditions are typically losing weight despite an increased appetite. With these metabolic disorders, the body cannot convert the food your pet is consuming into the energy that the body needs. Your dog's appetite will often increase as your dog's body attempts to get those nutrients by consuming more food. Unfortunately, this does not solve the problem, and your dog will begin to lose weight. 

Weight loss in these situations can be gradual. Other symptoms of these metabolic disorders include increased thirst and urination. If you notice any of these symptoms, schedule a visit with your veterinarian. Medication may be necessary to treat the underlying condition and stop your dog losing weight.


One of the most concerning causes of weight loss in dogs is cancer. Weight loss due to cancer occurs for a variety of different reasons. As cancer grows and spreads throughout the body, fast-dividing cancer cells consume an enormous amount of energy. This consumption of energy not only drains the vital nutrients that your dog’s body needs, but it can also interfere with the body's ability to utilize the few nutrients that are still available.

In the later stages of cancer, dogs may experience nausea and a decrease in appetite. Likewise, the tumor can be painful or make eating difficult. Oral tumors can cause obstructions that complicate swallowing. As the cancer continues to spread, a decrease in food consumption will result in a loss of body fat and muscle mass.

Unfortunately, by the time most pet owners notice the weight loss, the cancer can be advanced. Many cancers that cause weight loss are aggressive and challenging to treat. In some cases, they are life-threatening. Although cancer is usually associated with older dogs, it can affect dogs of all ages. Regular health screenings are critical to detect early signs of disease. 

Monitor your dog closely for signs of weight loss 

There are many reasons your dog may be losing weight. Some of these reasons are straightforward and easy to resolve. However, your dog's weight loss can also be a sign of more concerning health problems. Gradual weight loss is often a result of chronic conditions and can take a while for pet owners to notice. It is essential to keep a close eye on your pet's weight. If you notice your dog losing weight, take a closer look at what your pet is eating and if they are exhibiting any unusual symptoms or changes in activity. 

Weight loss is not something to be ignored. Knowing the common causes of weight loss can help you be more vigilant so you can catch potential problems early. If you are concerned about your dog losing weight, contact your veterinarian for further advice.

If you’ve noticed that your pup isn’t gaining weight, it might be a sign of fading puppy syndrome

Elizabeth Racine, DVM

Dr. Elizabeth Racine is a small animal general practice vet covering all things pet health and wellness.  Her special interests include veterinary behavior, nutrition, and internal medicine.  As a freelance writer, Dr. Racine has written content for major companies in the industry such as the American Kennel Club, Merck Animal Health, Bayer PetBasics, Elanco, and CareCredit.  In her free time, Dr. Racine enjoys playing trampoline dodgeball, hiking with her beagle Dasher, and spending time with her three mischievous cats.